Order Now Product Folder Support & Community Tools & Software Technical Documents LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 LM2735 520-kHz and 1.6-MHz Space-Efficient Boost and SEPIC DC/DC Regulator 1 Features 3 Description * * * The LM2735 device is an easy-to-use, space-efficient 2.1-A low-side switch regulator, ideal for Boost and SEPIC DC/DC regulation. The device provides all the active functions to provide local DC-DC conversion with fast-transient response and accurate regulation in the smallest PCB area. Switching frequency is internally set to either 520 kHz or 1.6 MHz, allowing the use of extremely small surface mount inductor and chip capacitors, while providing efficiencies of up to 90%. Current-mode control and internal compensation provide ease-of-use, minimal component count, and high-performance regulation over a wide range of operating conditions. External shutdown features an ultra-low standby current of 80 nA, ideal for portable applications. Tiny SOT-23, WSON, and MSOP-PowerPAD packages provide space savings. Additional features include internal soft start, circuitry to reduce inrush current, pulse-bypulse current limit, and thermal shutdown. 1 * * * * * * * Input Voltage Range: 2.7 V to 5.5 V Output Voltage Range: 3 V to 24 V 2.1-A Switch Current Over Full Temperature Range Current-Mode Control Logic High Enable Pin Ultra-Low Standby Current of 80 nA in Shutdown 170-m NMOS Switch 2% Feedback Voltage Accuracy Ease-of-Use, Small Total Solution Size - Internal Soft Start - Internal Compensation - Two Switching Frequencies - 520 kHz (LM2735-Y) - 1.6 MHz (LM2735-X) - Uses Small Surface Mount Inductors and Chip Capacitors - Tiny SOT-23, WSON, and MSOPPowerPADTM Packages Create a Custom Design Using the LM2735 With WEBENCH(R) Power Designer * * * * * PART NUMBER LM2735 PACKAGE BODY SIZE (NOM) WSON (6) 3.00 mm x 3.00 mm SOT-23 (5) 1.60 mm x 2.90 mm MSOP PowerPAD (8) 3.00 mm x 3.00 mm (1) For all available packages, see the orderable addendum at the end of the data sheet. 2 Applications * Device Information(1) LCD Display Backlighting For Portable Applications OLED Panel Power Supply USB-Powered Devices Digital Still and Video Cameras White LED Current Source For Automotive see LM2735-Q1 space Typical Boost Application Circuit Efficiency vs Load Current VO = 12 V VIN 2.7V-5.5V L1 12V D1 R2 R3 4 3 C2 2 5 C3 R1 1 C1 GND 1 An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications, intellectual property matters and other important disclaimers. PRODUCTION DATA. LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com Table of Contents 1 2 3 4 5 6 7 Features .................................................................. Applications ........................................................... Description ............................................................. Revision History..................................................... Pin Configuration and Functions ......................... Specifications......................................................... 1 1 1 2 3 4 6.1 6.2 6.3 6.4 6.5 6.6 4 4 4 4 5 7 Absolute Maximum Ratings ...................................... ESD Ratings: LM2735 .............................................. Recommended Operating Conditions....................... Thermal Information .................................................. Electrical Characteristics........................................... Typical Characteristics .............................................. Detailed Description .............................................. 9 7.1 7.2 7.3 7.4 Overview ................................................................... 9 Functional Block Diagram ....................................... 11 Feature Description................................................. 11 Device Functional Modes........................................ 14 8 Application and Implementation ........................ 14 8.1 Application Information............................................ 14 8.2 Typical Applications ................................................ 14 9 Power Supply Recommendations...................... 37 10 Layout................................................................... 37 10.1 Layout Guidelines ................................................. 37 10.2 Layout Examples................................................... 38 10.3 Thermal Considerations ........................................ 39 11 Device and Documentation Support ................. 48 11.1 11.2 11.3 11.4 11.5 11.6 Device Support...................................................... Documentation Support ........................................ Community Resources.......................................... Trademarks ........................................................... Electrostatic Discharge Caution ............................ Glossary ................................................................ 48 48 48 48 48 49 12 Mechanical, Packaging, and Orderable Information ........................................................... 49 4 Revision History NOTE: Page numbers for previous revisions may differ from page numbers in the current version. Changes from Revision H (March 2018) to Revision I * Added bullet to Applications list regarding automotive device LM2735-Q1 .......................................................................... 1 Changes from Revision G (August 2015) to Revision H * 2 Page Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and Mechanical, Packaging, and Orderable Information section. ................................................................................................. 1 Changes from Revision E (April 2013) to Revision F * Page Changed VFB Feedback Test Conditions from "TJ = -40C to 125C" To "TJ = 0C to 125C" for the SOT-23, WSON, and MSOP-PowerPAD devices................................................................................................................................. 5 Changes from Revision F (April 2013) to Revision G * Page Page Changed layout of National Data Sheet to TI format ........................................................................................................... 33 Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 5 Pin Configuration and Functions DBV Package 5-Pin SOT-23 Top View SW 1 DGN Package 8-Pin MSOP-PowerPAD Top View 5 VIN NC 1 8 NC PGND 2 7 SW VIN 3 6 AGND EN 4 5 FB GND 2 FB 3 4 EN NGG Package 6-Pin WSON Top View PGND 1 6 SW VIN 2 5 AGND EN 3 4 FB Pin Functions PIN NAME SOT-23 WSON MSOPPowerPAD I/O DESCRIPTION AGND -- 5 6 PWR Signal ground pin. Place the bottom resistor of the feedback network as close as possible to this pin and pin 4. For MSOP-PowerPAD, place the bottom resistor of the feedback network as close as possible to this pin and pin 5 EN 4 3 4 I Shutdown control input. Logic high enables operation. Do not allow this pin to float or be greater than VIN + 0.3 V. FB 3 4 5 I Feedback pin. Connect FB to external resistor-divider to set output voltage. GND 2 DAP DAP PWR NC -- -- 1, 8 -- PGND -- 1 2 PWR SW 1 6 7 O VIN 5 2 3 PWR Signal and power ground pin. Place the bottom resistor of the feedback network as close as possible to this pin. For WSON, connect to pin 1 and pin 5 on top layer. Place 4-6 vias from DAP to bottom layer GND plane. No Connect Power ground pin. Place PGND and output capacitor GND close together. Output switch. Connect to the inductor, output diode. Supply voltage for power stage, and input supply voltage. Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 3 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com 6 Specifications 6.1 Absolute Maximum Ratings See (1) MIN MAX VIN -0.5 7 V SW Voltage -0.5 26.5 V FB Voltage -0.5 3 V EN Voltage -0.5 7 V 150 C 220 C 150 C Junction temperature (2) Soldering information, infrared/convection reflow (15 s) Storage Temperature (1) (2) -65 UNIT If Military/Aerospace specified devices are required, contact the Texas Instruments Sales Office/ Distributors for availability and specifications. Thermal shutdown will occur if the junction temperature exceeds the maximum junction temperature of the device. 6.2 ESD Ratings: LM2735 VALUE V(ESD) (1) (2) (3) Electrostatic discharge Human body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1) (2) 2000 Charged device model (CDM), per JEDEC specification JESD22C101 (3) 1000 UNIT V JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. Manufacturing with less than 500-V HBM is possible if necessary precautions are taken. The human body model is a 100-pF capacitor discharged through a 1.5-k resistor into each pin. JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process. Manufacturing with less than 250-V CDM is possible if necessary precautions are taken. 6.3 Recommended Operating Conditions over operating free-air temperature range (unless otherwise noted) MIN VIN VSW VEN (1) Junction Temperature Range Power Dissipation (1) NOM MAX UNIT 2.7 5.5 V 3 24 V 0 VIN V -40 125 C 400 mW (Internal) SOT-23 Do not allow this pin to float or be greater than VIN + 0.3 V. 6.4 Thermal Information LM2735 THERMAL METRIC (1) Junction-to-ambient thermal resistance (2) RJA (2) NGG (WSON) DBV (SOT-23) DGN (MSOPPowerPAD) 6 PINS 5 PINS 8 PINS 54.9 164.2 59 C/W UNIT RJC(top) Junction-to-case (top) thermal resistance 50.9 115.3 51.2 C/W RJB Junction-to-board thermal resistance 29.3 27 35.8 C/W JT Junction-to-top characterization parameter 0.7 12.8 2.7 C/W JB Junction-to-board characterization parameter 29.4 26.5 35.6 C/W RJC(bot) Junction-to-case (bottom) thermal resistance 9.3 N/A 7.3 C/W (1) (2) 4 For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application report. Applies for packages soldered directly onto a 3" x 3" PC board with 2-oz. copper on 4 layers in still air. Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 6.5 Electrical Characteristics Limits are for TJ = 25C. Minimum and Maximum limits are specified through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25C, and are provided for reference purposes only. VIN = 5 V unless otherwise indicated under the Conditions column. PARAMETER TEST CONDITIONS -40C to TJ 125C (SOT-23) 0C to TJ 125C (SOT-23) -40C to TJ 125C (WSON) VFB Feedback Voltage 0C to TJ 125C (WSON) VFB/VIN Feedback Voltage Line Regulation IFB Feedback Input Bias Current TJ = 0C to 125C 1.23 1.28 0.06 %/V 1 2000 520 360 680 88% TJ = 25C 99% TJ = -40C to 125C 91% 5% 2% TJ = 25C 170 TJ = -40C to 125C 330 TJ = 25C 190 TJ = -40C to 125C 3 TJ = -40C to 125C A 2.1 4 TJ = 25C ms 7 TJ = -40C to 125C 11 TJ = 25C 3.4 TJ = -40C to 125C 80 TJ = 25C nA 2.3 TJ = -40C to 125C 2.65 TJ = 25C 1.9 TJ = -40C to 125C V 1.7 Submit Documentation Feedback Product Folder Links: LM2735 mA 7 All Options VEN = 0 V Copyright (c) 2007-2018, Texas Instruments Incorporated m 350 TJ = 25C VIN Falling kHz 96% LM2735-Y Undervoltage Lockout A 1600 1200 LM2735-X VIN Rising UVLO 1.29 1.255 TJ = -40C to 125C LM2735-Y Quiescent Current (shutdown) 1.281 1.22 TJ = 25C LM2735-X IQ TJ = -40C to 125C TJ = -40C to 125C Quiescent Current (switching) V 1.255 TJ = 25C WSON Soft Start 1.229 TJ = -40C to 125C Switch ON-Resistance SS TJ = 0C to 125C TJ = 25C SOT-23 and MSOP-PowerPAD Switch Current Limit 1.285 1.255 0.1 Maximum Duty Cycle ICL 1.225 TJ = 25C TJ = -40C to 125C LM2735-Y RDS(ON) TJ = -40C to 125C TJ = 25C Switching Frequency Minimum Duty Cycle 1.274 1.255 VIN = 2.7 V to 5.5 V LM2735-X DMIN 1.28 1.236 TJ = 25C 0C to TJ 125C (MSOPPowerPAD) MAX UNIT 1.255 TJ = 0C to 125C TJ = 25C LM2735-Y DMAX 1.23 TJ = 25C -40C to TJ 125C (MSOP-PowerPAD) TYP 1.255 TJ = -40C to 125C TJ = 25C LM2735-X FSW MIN TJ = 25C 5 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com Electrical Characteristics (continued) Limits are for TJ = 25C. Minimum and Maximum limits are specified through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25C, and are provided for reference purposes only. VIN = 5 V unless otherwise indicated under the Conditions column. PARAMETER TEST CONDITIONS MIN TYP MAX UNIT Shutdown Threshold Voltage See Enable Threshold Voltage See (1), TJ = -40C to 125C I-SW Switch Leakage VSW = 24 V 1 A I-EN Enable Pin Current Sink/Source 100 nA VEN_TH TSD (1) (2) 6 (1) , TJ = -40C to 125C 0.4 V 1.8 Thermal Shutdown Temperature (2) 160 Thermal Shutdown Hysteresis 10 C Do not allow this pin to float or be greater than VIN + 0.3 V. Thermal shutdown will occur if the junction temperature exceeds the maximum junction temperature of the device. Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 6.6 Typical Characteristics Figure 1. Current Limit vs Temperature Figure 2. FB Pin Voltage vs Temperature Figure 3. Oscillator Frequency vs Temperature - "X" Figure 4. Oscillator Frequency vs Temperature - "Y" Figure 5. Typical Maximum Output Current vs VIN Figure 6. RDSON vs Temperature Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 7 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com Typical Characteristics (continued) VO = 20 V VO = 20 V Figure 7. LM2735X Efficiency vs Load Current VO = 12 V 8 Figure 8. LM2735Y Efficiency vs Load Current VO = 12 V Figure 9. LM2735X Efficiency vs Load Current Figure 10. LM2735Y Efficiency vs Load Current Figure 11. Output Voltage Load Regulation Figure 12. Output Voltage Line Regulation Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 7 Detailed Description 7.1 Overview The LM2735 device is highly efficient and easy-to-use switching regulator for boost and SEPIC applications. The device provides regulated DC output with fast transient response. Device architecture (current mode control) and internal compensation enable solutions with minimum number of external components. Additionally high switching frequency allows for use of small external passive components (chip capacitors, SMD inductors) and enables power solutions with very small PCB area. LM2735 also provides features such as soft start, pulse-bypulse current-limit, and thermal shutdown. 7.1.1 Theory of Operation The LM2735 is a constant-frequency PWM boost regulator IC that delivers a minimum of 2.1 A peak switch current. The regulator has a preset switching frequency of either 520 kHz or 1.6 MHz. This high frequency allows the device to operate with small surface mount capacitors and inductors, resulting in a DC-DC converter that requires a minimum amount of board space. The LM2735 is internally compensated, so it is simple to use, and requires few external components. The device uses current-mode control to regulate the output voltage. The following operating description of the LM2735 refers to the simplified internal block diagram (Functional Block Diagram), the simplified schematic (Figure 13), and its associated waveforms (Figure 14). The LM2735 supplies a regulated output voltage by switching the internal NMOS control switch at constant frequency and variable duty cycle. A switching cycle begins at the falling edge of the reset pulse generated by the internal oscillator. When this pulse goes low, the output control logic turns on the internal NMOS control switch. During this on-time, the SW pin voltage (VSW) decreases to approximately GND, and the inductor current (IL) increases with a linear slope. IL is measured by the current sense amplifier, which generates an output proportional to the switch current. The sensed signal is summed with the corrective ramp of the regulator and compared to the error amplifier's output, which is proportional to the difference between the feedback voltage and VREF. When the PWM comparator output goes high, the output switch turns off until the next switching cycle begins. During the switch off-time, inductor current discharges through diode D1, which forces the SW pin to swing to the output voltage plus the forward voltage (VD) of the diode. The regulator loop adjusts the duty cycle (D) to maintain a constant output voltage . I L (t) + VL (t) - D1 L1 I C (t) Control + VIN + Q1 VSW( t ) C1 VO(t) - Figure 13. Simplified Schematic Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 9 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com Overview (continued) VO + VD Vsw (t) t VIN VL(t) t VIN - VOUT - VD I L (t) iL t I DIODE (t) t ( iL - - i OUT ) I Capacitor (t) t - i OUT 'v VOUT (t) DTS TS Figure 14. Typical Waveforms 10 Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 7.2 Functional Block Diagram EN VIN ThermalSHDN Control Logic + UVLO = 2.3V Oscillator Corrective - Ramp SW cv S R R Q 1.6 MHz + + - FB VREF = 1.255V NMOS Internal Compensation ILIMIT Soft-Start ISENSE-AMP + - GND 7.3 Feature Description 7.3.1 Current Limit The LM2735 uses cycle-by-cycle current limiting to protect the internal NMOS switch. It is important to note that this current limit will not protect the output from excessive current during an output short circuit. The input supply is connected to the output by the series connection of an inductor and a diode. If a short circuit is placed on the output, excessive current can damage both the inductor and diode. 7.3.2 Thermal Shutdown Thermal shutdown limits total power dissipation by turning off the output switch when the IC junction temperature exceeds 160C. After thermal shutdown occurs, the output switch does not turn on until the junction temperature drops to approximately 150C. 7.3.3 Soft Start This function forces VOUT to increase at a controlled rate during start-up. During soft start, the reference voltage of the error amplifier ramps to its nominal value of 1.255 V in approximately 4 ms. This forces the regulator output to ramp up in a more linear and controlled fashion, which helps reduce inrush current. 7.3.4 Compensation The LM2735 uses constant-frequency peak current mode control. This mode of control allows for a simple external compensation scheme that can be optimized for each application. A complicated mathematical analysis can be completed to fully explain the internal and external compensation of the LM2735, but for simplicity, a graphical approach with simple equations will be used. Below is a Gain and Phase plot of a LM2735 that produces a 12-V output from a 5-V input voltage. The Bode plot shows the total loop Gain and Phase without external compensation. Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 11 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com Feature Description (continued) 80 180 gm-Pole 60 RC-Pole 90 40 dB 20 0 -20 Vi = 5V Vo = 12V Io = 500 mA Co = 10 PF Lo = 5 PH 0 gm-Zero -90 -40 RHP-Zero -60 -80 10 100 1k 10k 100k -180 1M FREQUENCY Figure 15. LM2735 Without External Compensation One can see that the crossover frequency is fine, but the phase margin at 0 dB is very low (22). A zero can be placed just above the crossover frequency so that the phase margin will be bumped up to a minimum of 45. Below is the same application with a zero added at 8 kHz. 80 gm-Pole 60 RC-Pole 40 Vi = 5V Vo = 12V Io = 500 mA Co = 10 mF Lo = 5 mH 180 90 D = 0.625 Cf = 220 pF gm-zero 0 0 Fz-cf = 8 kHz RHP-Zero = 107 kHz -20 Fp-cf = 77 kHz Fp-rc = 660 Hz -90 -40 Ext (Cf) -Zero -60 Ext (Cf)-Pole RHP-Zero -180 -80 10 100 1k 10k 100k 1M dB 20 FREQUENCY Figure 16. LM2735 With External Compensation The simplest method to determine the compensation component value is as follows. Set the output voltage with the following equation. VOUT * - 1 x R1 R 2 = (c) VREF where * R1 is the bottom resistor and R2 is the resistor tied to the output voltage. (1) The next step is to calculate the value of C3. The internal compensation has been designed so that when a zero is added from 5 kHz to 10 kHz, the converter will have good transient response with plenty of phase margin for all input and output voltage combinations. 1 FZERO - CF = = 5 kHz o 10 kHz 2S(R2 x Cf) (2) 12 Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 Feature Description (continued) Lower output voltages will have the zero set closer to 10 kHz, and higher output voltages will usually have the zero set closer to 5 kHz. TI recommends obtaining a Gain and Phase plot for your actual application. See Application and Implementation to obtain examples of working applications and the associated component values. Pole at origin due to internal GM amplifier: FP-ORIGIN (3) Pole due to output load and capacitor: 1 FP- RC = 2S(R Load COUT) (4) This equation only determines the frequency of the pole for perfect current mode control (CMC). That is, it doesn't take into account the additional internal artificial ramp that is added to the current signal for stability reasons. By adding artificial ramp, you begin to move away from CMC to voltage mode control (VMC). The artifact is that the pole due to the output load and output capacitor will actually be slightly higher in frequency than calculated. In this example, it is calculated at 650 Hz, but in reality, it is around 1 kHz. The zero created with capacitor C3 & resistor R2: VO R2 C3 VFB R LOAD R1 Figure 17. Setting External Pole-Zero FZERO - CF = 1 2S(R2 x C3) (5) There is an associated pole with the zero that was created in the above equation. FPOLE - CF = 1 2S((R1 R2) x C3) (6) It is always higher in frequency than the zero. A right-half plane zero (RHPZ) is inherent to all boost converters. One must remember that the gain associated with a right-half plane zero increases at 20 dB per decade, but the phase decreases by 45 per decade. For most applications there is little concern with the RHPZ due to the fact that the frequency at which it shows up is well beyond crossover, and has little to no effect on loop stability. One must be concerned with this condition for large inductor values and high output currents. 2 RHPZERO = (D') RLoad 2S x L (7) There are miscellaneous poles and zeros associated with parasitics internal to the LM2735, external components, and the PCB. They are located well over the crossover frequency, and for simplicity are not discussed. Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 13 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com 7.4 Device Functional Modes 7.4.1 Enable Pin and Shutdown Mode The LM2735 has a shutdown mode that is controlled by the Enable pin (EN). When a logic low voltage is applied to EN, the part is in shutdown mode and its quiescent current drops to typically 80 nA. Switch leakage adds up to another 1 A from the input supply. The voltage at this pin should never exceed VIN + 0.3 V. 8 Application and Implementation NOTE Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI's customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality. 8.1 Application Information The device will operate with input voltage in the range of 2.7 V to 5.5 V and provide regulated output voltage. This device is optimized for high-efficiency operation with minimum number of external components. For component selection, see Detailed Design Procedure. 8.2 Typical Applications 8.2.1 LM2735X SOT-23 Design Example 1 L1 4 R3 EN 3 FB 2 GND VIN 5 Vin 12V 1 SW D1 C1 R2 C2 C3 R LOAD R1 Figure 18. LM2735X (1.6 MHz): VIN = 5 V, VOUT = 12 V @ 350 mA 8.2.1.1 Design Requirements The device must be able to operate at any voltage within input voltage range. The load current needs to be defined in order to properly size the inductor, input capacitor, and output capacitor. The inductor must be able to handle full expected load current as well as the peak current generated during load transients and start-up. The inrush current at startup will depend on the output capacitor selection. More details are provided in Detailed Design Procedure. The device has an enable pin (EN) that is used to enable and disable the device. This pin is active high and care should be taken that voltage on this pin does not exceed VIN + 0.3 V. 14 Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 Typical Applications (continued) 8.2.1.2 Detailed Design Procedure Table 1. Bill of Materials PART ID PART VALUE MANUFACTURER PART NUMBER U1 2.1-A Boost Regulator TI LM2735XMF C1, Input Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M C2 Output Capacitor 10 F, 25 V, X5R TDK C3216X5R1E106M C3 Comp Capacitor 330 pF TDK C1608X5R1H331K D1, Catch Diode 0.4 Vf Schottky 1 A, 20 VR ST STPS120M L1 15 H 1.5 A Coilcraft MSS5131-153ML R1 10.2 k, 1% Vishay CRCW06031022F R2 86.6 k, 1% Vishay CRCW06038662F R3 100 k, 1% Vishay CRCW06031003F 8.2.1.2.1 Custom Design With WEBENCH(R) Tools Click here to create a custom design using the LM2735 device with the WEBENCH(R) Power Designer. 1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements. 2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial. 3. Compare the generated design with other possible solutions from Texas Instruments. The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time pricing and component availability. In most cases, these actions are available: * Run electrical simulations to see important waveforms and circuit performance * Run thermal simulations to understand board thermal performance * Export customized schematic and layout into popular CAD formats * Print PDF reports for the design, and share the design with colleagues Get more information about WEBENCH tools at www.ti.com/WEBENCH. 8.2.1.2.2 Inductor Selection The duty cycle (D) can be approximated quickly using the ratio of output voltage (VO) to input voltage (VIN): VOUT 1 * 1 = = VIN (c)1 - D Dc (8) Therefore: D= VOUT - VIN VOUT (9) Power losses due to the diode (D1) forward voltage drop, the voltage drop across the internal NMOS switch, the voltage drop across the inductor resistance (RDCR), and switching losses must be included to calculate a more accurate duty cycle (see Calculating Efficiency, and Junction Temperature for a detailed explanation). A more accurate formula for calculating the conversion ratio is: VOUT K = c D VIN where * equals the efficiency of the LM2735 application. (10) The inductor value determines the input ripple current. Lower inductor values decrease the size of the inductor, but increase the input ripple current. An increase in the inductor value will decrease the input ripple current. Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 15 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com 'i L I L (t) iL VIN - VOUT VIN L L DTS TS t Figure 19. Inductor Current 2'iL VIN * = DTS (c) L VIN * x DTS AiL = (c) 2L (11) A good design practice is to design the inductor to produce 10% to 30% ripple of maximum load. From the previous equations, the inductor value is then obtained. VIN * x DTS L = (c)2 x 'iL where * 1/TS = FSW = switching frequency (12) Ensure that the minimum current limit (2.1 A) is not exceeded, so the peak current in the inductor must be calculated. The peak current (ILPK ) in the inductor is calculated by: ILpk = IIN + IL (13) ILpk = IOUT / D' + IL (14) or When selecting an inductor, make sure that it is capable of supporting the peak input current without saturating. Inductor saturation will result in a sudden reduction in inductance and prevent the regulator from operating correctly. Because of the speed of the internal current limit, the peak current of the inductor need only be specified for the required maximum input current. For example, if the designed maximum input current is 1.5 A and the peak current is 1.75 A, then the inductor should be specified with a saturation current limit of >1.75 A. There is no need to specify the saturation or peak current of the inductor at the 3-A typical switch current-limit. Because of the operating frequency of the LM2735, ferrite based inductors are preferred to minimize core losses. This presents little restriction since the variety of ferrite-based inductors is huge. Lastly, inductors with lower series resistance (DCR) will provide better operating efficiency. For recommended inductors, see the following design examples. 8.2.1.2.3 Input Capacitor An input capacitor is necessary to ensure that VIN does not drop excessively during switching transients. The primary specifications of the input capacitor are capacitance, voltage, RMS current rating, and ESL (Equivalent Series Inductance). The recommended input capacitance is 10 F to 44 F depending on the application. The capacitor manufacturer specifically states the input voltage rating. Make sure to check any recommended deratings and also verify if there is any significant change in capacitance at the operating input voltage and the operating temperature. The ESL of an input capacitor is usually determined by the effective cross sectional area of the current path. At the operating frequencies of the LM2735, certain capacitors may have an ESL so large that the resulting impedance (2fL) will be higher than that required to provide stable operation. As a result, surface mount capacitors are strongly recommended. Multilayer ceramic capacitors (MLCC) are good choices for both input and output capacitors and have very low ESL. For MLCCs, TI recommends using X7R or X5R dielectrics. Consult capacitor manufacturer datasheet to see how rated capacitance varies over operating conditions. 16 Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 8.2.1.2.4 Output Capacitor The LM2735 operates at frequencies allowing the use of ceramic output capacitors without compromising transient response. Ceramic capacitors allow higher inductor ripple without significantly increasing output ripple. The output capacitor is selected based upon the desired output ripple and transient response. The initial current of a load transient is provided mainly by the output capacitor. The output impedance will therefore determine the maximum voltage perturbation. The output ripple of the converter is a function of the reactance of the capacitor and its equivalent series resistance (ESR): * VOUT x D AVOUT = AIL x R ESR + 2 x F x R x C SW Load OUT (c) (15) When using MLCCs, the ESR is typically so low that the capacitive ripple may dominate. When this occurs, the output ripple will be approximately sinusoidal and 90 phase shifted from the switching action. Given the availability and quality of MLCCs and the expected output voltage of designs using the LM2735, there is really no need to review any other capacitor technologies. Another benefit of ceramic capacitors is their ability to bypass high-frequency noise. A certain amount of switching edge noise will couple through parasitic capacitances in the inductor to the output. A ceramic capacitor will bypass this noise while a tantalum will not. Since the output capacitor is one of the two external components that control the stability of the regulator control loop, most applications will require a minimum at 4.7 F of output capacitance. Like the input capacitor, recommended multilayer ceramic capacitors are X7R or X5R. Again, verify actual capacitance at the desired operating voltage and temperature. 8.2.1.2.5 Setting the Output Voltage The output voltage is set using the following equation where R1 is connected between the FB pin and GND, and R2 is connected between VOUT and the FB pin. VO R2 C3 VFB R LOAD R1 Figure 20. Setting Vout A good value for R1 is 10 k. VOUT * - 1 x R1 R 2 = (c) VREF (16) Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 17 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com 8.2.1.3 Application Curves Vin = 3.3 V Vout = 12 V Vin = 5 V Figure 21. LM2735X Typical Startup Waveform Vout = 12 V Figure 22. LM2735X Typical Startup Waveform 8.2.2 LM2735Y SOT-23 Design Example 2 L1 3 4 FB EN R3 2 GND VIN 12V 1 5 SW Vin D1 C1 R2 C2 C3 R LOAD R1 Figure 23. LM2735Y (520 kHz): VIN = 5 V, VOUT = 12 V at 350 mA 18 PART ID PART VALUE MANUFACTURER U1 2.1-A Boost Regulator TI PART NUMBER LM2735YMF C1, Input Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M C2 Output Capacitor 10 F, 25 V, X5R TDK C3216X5R1E106M C3 Comp Capacitor 330 pF TDK C1608X5R1H331K D1, Catch Diode 0.4 Vf Schottky 1 A, 20 VR ST STPS120M L1 33 H 1.5 A Coilcraft DS3316P-333ML R1 10.2 k, 1% Vishay CRCW06031022F R2 86.6 k, 1% Vishay CRCW06038662F R3 100 k, 1% Vishay CRCW06031003F Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 8.2.3 LM2735X WSON Design Example 3 VIN L1 LM2735 R3 C1 C2 D1 1 6 2 5 R2 C5 RLOAD 3 C3 4 C4 R1 Figure 24. LM2735X (1.6 MHz): VIN = 3.3 V, VOUT = 12 V at 350 mA PART ID PART VALUE MANUFACTURER U1 2.1-A Boost Regulator TI PART NUMBER LM2735XSD C1 Input Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M TDK C3216X5R1E106M TDK C1608X5R1H331K C2 Input Capacitor No Load C3 Output Capacitor 10 F, 25 V, X5R C4 Output Capacitor No Load C5 Comp Capacitor 330 pF D1, Catch Diode 0.4 Vf Schottky 1 A, 20 VR ST STPS120M L1 6.8 H 2 A Coilcraft DO1813H-682ML R1 10.2 k, 1% Vishay CRCW06031022F R2 86.6 k, 1% Vishay CRCW06038662F R3 100 k, 1% Vishay CRCW06031003F Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 19 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com 8.2.4 LM2735Y WSON Design Example 4 VIN L1 LM2735 R3 C1 C2 D1 1 6 2 5 R2 C5 RLOAD 3 C3 4 C4 R1 Figure 25. LM2735Y (520 kHz): VIN = 3.3 V, VOUT = 12 V at 350 mA 20 PART ID PART VALUE MANUFACTURER U1 2.1-A Boost Regulator TI PART NUMBER LM2735YSD C1 Input Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M TDK C3216X5R1E106M TDK C1608X5R1H331K C2 Input Capacitor No Load C3 Output Capacitor 10 F, 25 V, X5R C4 Output Capacitor No Load C5 Comp Capacitor 330 pF D1, Catch Diode 0.4 Vf Schottky 1 A, 20 VR ST STPS120M L1 15 H 2 A Coilcraft MSS5131-153ML R1 10.2 k, 1% Vishay CRCW06031022F R2 86.6 k, 1% Vishay CRCW06038662F R3 100 k, 1% Vishay CRCW06031003F Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 8.2.5 LM2735Y MSOP-PowerPAD Design Example 5 VIN L1 D1 R3 LM2735 C1 C2 1 NC NC 8 2 PGND SW 7 3 VIN R2 C5 AGND 6 4 EN R LOAD FB 5 C4 C3 R1 Figure 26. LM2735Y (520 kHz): VIN = 3.3 V, VOUT = 12 V at 350 mA PART ID PART VALUE MANUFACTURER PART NUMBER U1 2.1-A Boost Regulator TI LM2735YMY C1 Input Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M C2 Input Capacitor No Load C3 Output Capacitor 10 F, 25 V, X5R TDK C3216X5R1E106M C4 Output Capacitor No Load C5 Comp Capacitor 330 pF TDK C1608X5R1H331K D1, Catch Diode 0.4 Vf Schottky 1 A, 20 VR ST STPS120M L1 15 H 1.5 A Coilcraft MSS5131-153ML R1 10.2 k, 1% Vishay CRCW06031022F R2 86.6 k, 1% Vishay CRCW06038662F R3 100 k, 1% Vishay CRCW06031003F Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 21 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com 8.2.6 LM2735X SOT-23 Design Example 6 L1 3 4 FB SHDN R3 2 GND VIN 5V 1 5 SW Vin D1 C1 R2 C2 C3 R LOAD R1 Figure 27. LM2735X (1.6 MHz): VIN = 3 V, VOUT = 5 V at 500 mA 22 PART ID PART VALUE MANUFACTURER U1 2.1-A Boost Regulator TI LM2735XMF C1, Input Capacitor 10 F, 6.3 V, X5R TDK C2012X5R0J106K C2, Output Capacitor 10 F, 6.3 V, X5R TDK C2012X5R0J106K C3 Comp Capacitor 1000 pF TDK C1608X5R1H102K D1, Catch Diode 0.4 Vf Schottky 1 A, 20 VR ST STPS120M L1 10 H 1.2 A Coilcraft DO1608C-103ML R1 10.0 k, 1% Vishay CRCW08051002F R2 30.1 k, 1% Vishay CRCW08053012F R3 100 k, 1% Vishay CRCW06031003F Submit Documentation Feedback PART NUMBER Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 8.2.7 LM2735Y SOT-23 Design Example 7 L1 3 4 R3 FB SHDN 2 GND VIN 5V 1 5 SW Vin D1 C1 R2 C2 C3 R LOAD R1 Figure 28. LM2735Y (520 kHz): VIN = 3 V, VOUT = 5 V at 750 mA PART ID PART VALUE MANUFACTURER U1 2.1-A Boost Regulator TI PART NUMBER LM2735YMF C1 Input Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M C2 Output Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M C3 Comp Capacitor 1000 pF TDK C1608X5R1H102K D1, Catch Diode 0.4 Vf Schottky 1 A, 20 VR ST STPS120M L1 22 H 1.2 A Coilcraft MSS5131-223ML R1 10.0 k, 1% Vishay CRCW08051002F R2 30.1 k, 1% Vishay CRCW08053012F R3 100 k, 1% Vishay CRCW06031003F Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 23 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com 8.2.8 LM2735X SOT-23 Design Example 8 L1 3 4 R3 FB SHDN 2 GND VIN 20V 1 5 SW Vin D1 C1 R2 C2 C3 R LOAD R1 Figure 29. LM2735X (1.6 MHz): VIN = 3.3 V, Vout = 20 V at 100 mA 24 PART ID PART VALUE MANUFACTURER U1 2.1-A Boost Regulator TI LM2735XMF C1, Input Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M C2, Output Capacitor 4.7 F, 25 V, X5R TDK C3216X5R1E475K C3 Comp Capacitor 470 pF TDK C1608X5R1H471K D1, Catch Diode 0.4 Vf Schottky 500 mA, 30 VR Vishay MBR0530 L1 10 H 1.2 A Coilcraft DO1608C-103ML R1 10.0 k, 1% Vishay CRCW06031002F R2 150 k, 1% Vishay CRCW06031503F R3 100 k, 1% Vishay CRCW06031003F Submit Documentation Feedback PART NUMBER Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 8.2.9 LM2735Y SOT-23 Design Example 9 L1 3 4 R3 FB SHDN 2 GND VIN 20V 1 5 SW Vin D1 C1 C3 R2 C2 R LOAD R1 Figure 30. LM2735Y (520 kHz): VIN = 3.3 V, VOUT = 20 V at 100 mA PART ID PART VALUE MANUFACTURER U1 2.1-A Boost Regulator TI PART NUMBER LM2735YMF C1 Input Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M C2 Output Capacitor 10 F, 25 V, X5R TDK C3216X5R1E106M C3 Comp Capacitor 470 pF TDK C1608X5R1H471K D1, Catch Diode 0.4 Vf Schottky 500 mA, 30 VR Vishay MBR0530 L1 33 H 1.5 A Coilcraft DS3316P-333ML R1 10.0 k, 1% Vishay CRCW06031002F R2 150.0 k, 1% Vishay CRCW06031503F R3 100 k, 1% Vishay CRCW06031003F Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 25 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com 8.2.10 LM2735X WSON Design Example 10 VIN L1 LM2735 R3 C1 C2 D1 1 6 2 5 R2 C5 RLOAD 3 C3 4 C4 R1 Figure 31. LM2735X (1.6 MHz): VIN = 3.3 V, VOUT = 20 V at 150 mA 26 PART ID PART VALUE MANUFACTURER U1 2.1-A Boost Regulator TI PART NUMBER LM2735XSD C1 Input Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M C2 Input Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M C3 Output Capacitor 10 F, 25 V, X5R TDK C3216X5R1E106M C4 Output Capacitor No Load C5 Comp Capacitor 470 pF TDK C1608X5R1H471K D1, Catch Diode 0.4 Vf Schottky 500 mA, 30 VR Vishay MBR0530 L1 8.2 H 2 A Coilcraft DO1813H-822ML R1 10.0 k, 1% Vishay CRCW06031002F R2 150 k, 1% Vishay CRCW06031503F R3 100 k, 1% Vishay CRCW06031003F Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 8.2.11 LM2735Y WSON Design Example 11 VIN L1 LM2735 R3 C1 C2 D1 1 6 2 5 R2 C5 RLOAD 3 C3 4 C4 R1 Figure 32. LM2735Y (520 kHz): VIN = 3.3 V, VOUT = 20 V at 150 mA PART ID PART VALUE MANUFACTURER U1 2.1-A Boost Regulator TI PART NUMBER LM2735YSD C1 Input Capacitor 10 F, 6.3 V, X5R TDK C2012X5R0J106K C2 Input Capacitor 10 F, 6.3 V, X5R TDK C2012X5R0J106K C3 Output Capacitor 10 F, 25 V, X5R TDK C3216X5R1E106M C4 Output Capacitor No Load C5 Comp Capacitor 470 pF TDK C1608X5R1H471K D1, Catch Diode 0.4 Vf Schottky 500 mA, 30 VR Vishay MBR0530 L1 22 H 1.5 A Coilcraft DS3316P-223ML R1 10.0 k, 1% Vishay CRCW06031002F R2 150 k, 1% Vishay CRCW06031503F R3 100 k, 1% Vishay CRCW06031003F Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 27 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com 8.2.12 LM2735X WSON SEPIC Design Example 12 VIN VO L1 D1 C6 LM2735 C1 C2 1 6 2 5 3 4 L2 R2 R3 C5 C3 C4 R1 Figure 33. LM2735X (1.6 MHz): VIN = 2.7 V - 5 V, VOUT = 3.3 V at 500 mA 28 PART ID PART VALUE MANUFACTURER U1 2.1-A Boost Regulator TI LM2735XSD C1 Input Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M TDK C3216X5R1E106M C2 Input Capacitor No Load C3 Output Capacitor 10 F, 25 V, X5R C4 Output Capacitor No Load PART NUMBER C5 Comp Capacitor 2200 pF TDK C1608X5R1H222K C6 2.2 F 16 V TDK C2012X5R1C225K D1, Catch Diode 0.4 Vf Schottky 1 A, 20 VR ST STPS120M L1 6.8 H Coilcraft DO1608C-682ML L2 6.8 H Coilcraft DO1608C-682ML R1 10.2 k, 1% Vishay CRCW06031002F R2 16.5 k, 1% Vishay CRCW06031652F R3 100 k, 1% Vishay CRCW06031003F Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 8.2.13 LM2735Y MSOP-PowerPAD SEPIC Design Example 13 VIN L1 D1 C6 R3 LM2735 C1 C2 1 NC NC 8 2 PGND SW 7 3 VIN R2 L2 C5 AGND 6 4 EN R LOAD FB 5 C4 C3 R1 Figure 34. LM2735Y (520 kHz): VIN = 2.7 V - 5 V, VOUT = 3.3 V at 500 mA PART ID PART VALUE MANUFACTURER PART NUMBER U1 2.1-A Boost Regulator TI LM2735YMY C1 Input Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M C2 Input Capacitor No Load C3 Output Capacitor 10 F, 25 V, X5R TDK C3216X5R1E106M C4 Output Capacitor No Load C5 Comp Capacitor 2200 pF TDK C1608X5R1H222K C2012X5R1C225K C6 2.2 F 16 V TDK D1, Catch Diode 0.4 Vf Schottky 1 A, 20 VR ST STPS120M L1 15 H 1.5 A Coilcraft MSS5131-153ML L2 15 H 1.5 A Coilcraft MSS5131-153ML R1 10.2 k, 1% Vishay CRCW06031002F R2 16.5 k, 1% Vishay CRCW06031652F R3 100 k, 1% Vishay CRCW06031003F Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 29 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com 8.2.14 LM2735X SOT-23 LED Design Example 14 L1 R3 3 FB 2 4 SHDN Vin C2 D1 1 SW 5 Vin C1 R1 R2 DIM - CTRL Figure 35. LM2735X (1.6 MHz): VIN = 2.7 V - 5 V, VOUT = 20 V at 50 mA 30 PART ID PART VALUE MANUFACTURER PART NUMBER U1 2.1-A Boost Regulator TI LM2735XMF C1 Input Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M C2 Output Capacitor 4.7 F, 25 V, X5R TDK C3216JB1E475K D1, Catch Diode 0.4 Vf Schottky 500 mA, 30 VR Vishay MBR0530 L1 15 H 1.5 A Coilcraft MSS5131-153ML R1 25.5 , 1% Vishay CRCW080525R5F R2 100 , 1% Vishay CRCW08051000F R3 100 k, 1% Vishay CRCW06031003F Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 8.2.15 LM2735Y WSON FlyBack Design Example 15 + 12V D1 R2 Cf T1 V IN C2 R LOAD R1 LM2735 R3 1 C3 6 R LOAD C1 2 5 3 4 D2 - 12V Figure 36. LM2735Y (520 kHz): VIN = 5 V, VOUT = 12 V 150 mA PART ID PART VALUE MANUFACTURER U1 2.1-A Boost Regulator TI PART NUMBER LM2735YSD C1 Input Capacitor 22 F, 6.3 V, X5R TDK C2012X5R0J226M C2 Output Capacitor 10 F, 25 V, X5R TDK C3216X5R1E106M C3 Output Capacitor 10 F, 25 V, X5R TDK C3216X5R1E106M Cf Comp Capacitor 330 pF TDK C1608X5R1H331K D1, D2 Catch Diode 0.4 Vf Schottky 500 mA, 30 VR Vishay MBR0530 R1 10.0 k, 1% Vishay CRCW06031002F R2 86.6 k, 1% Vishay CRCW06038662F R3 100 k, 1% Vishay CRCW06031003F T1 Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 31 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com 8.2.16 LM2735X SOT-23 LED Design Example 16 VRAIL > 5.5 V Application D1 L1 VPWR R4 4 R3 C4 3 2 5 D2 R2 LM2735 EN C1 C2 1 R1 C3 Figure 37. LM2735X (1.6 MHz): VPWR = 9 V, VOUT = 12 V at 500 mA 32 PART ID PART VALUE MANUFACTURER U1 2.1-A Boost Regulator TI LM2735XMF C1, Input Capacitor 10 F, 6.3 V, X5R TDK C2012X5R0J106K C2, Output Capacitor 10 F, 25 V, X5R TDK C3216X5R1E106M C3 VIN Cap 0.1 F, 6.3 V, X5R TDK C2012X5R0J104K C4 Comp Capacitor 1000 pF TDK C1608X5R1H102K D1, Catch Diode 0.4 Vf Schottky 1 A, 20 VR ST STPS120M D2 3.3-V Zener, SOT-23 Diodes Inc BZX84C3V3 L1 6.8 H 2 A Coilcraft DO1813H-682ML R1 10.0 k, 1% Vishay CRCW08051002F R2 86.6 k, 1% Vishay CRCW08058662F R3 100 k, 1% Vishay CRCW06031003F R4 499 , 1% Vishay CRCW06034991F Submit Documentation Feedback PART NUMBER Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 8.2.17 LM2735X SOT-23 LED Design Example 17 Two-Input Voltage Rail Application D1 L1 VPWR LM2735 EN C1 4 R3 R2 3 2 VIN 5 C4 R1 1 C2 C3 Figure 38. LM2735X (1.6 MHz): VPWR = 9 V in = 2.7 V - 5.5 V, VOUT = 12 V at 500 mA PART ID PART VALUE MANUFACTURER PART NUMBER U1 2.1-A Boost Regulator TI LM2735XMF C1, Input Capacitor 10 F, 6.3 V, X5R TDK C2012X5R0J106K C2, Output Capacitor 10 F, 25 V, X5R TDK C3216X5R1E106M C3 VIN Capacitor 0.1 F, 6.3 V, X5R TDK C2012X5R0J104K C4 Comp Capacitor 1000 pF TDK C1608X5R1H102K D1, Catch Diode 0.4 Vf Schottky 1 A, 20 VR ST STPS120M L1 6.8 H 2 A Coilcraft DO1813H-682ML R1 10.0 k, 1% Vishay CRCW08051002F R2 86.6 k, 1% Vishay CRCW08058662F R3 100 k, 1% Vishay CRCW06031003F Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 33 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com 8.2.18 SEPIC Converter VIN VO L1 C6 D1 LM2735 C1 C2 1 6 2 5 3 4 L2 R3 R2 C5 C3 C4 R1 Figure 39. SEPIC Converter Schematic 8.2.18.1 Detailed Design Procedure The LM2735 can easily be converted into a SEPIC converter. A SEPIC converter has the ability to regulate an output voltage that is either larger or smaller in magnitude than the input voltage. Other converters have this ability as well (CUK and Buck-Boost), but usually create an output voltage that is opposite in polarity to the input voltage. This topology is a perfect fit for Lithium Ion battery applications where the input voltage for a single-cell Li-Ion battery will vary from 3 V to 4.5 V and the output voltage is somewhere in-between. Most of the analysis of the LM2735 Boost Converter is applicable to the LM2735 SEPIC Converter. 8.2.18.1.1 SEPIC Design Guide SEPIC Conversion ratio without loss elements: Vo D = D' VIN (17) Therefore: D= VO VO + VIN (18) 8.2.18.1.2 Small Ripple Approximation In a well-designed SEPIC converter, the output voltage, input voltage ripple, and inductor ripple is small in comparison to the DC magnitude. Therefore, it is a safe approximation to assume a DC value for these components. The main objective of the Steady State Analysis is to determine the steady state duty-cycle, voltage and current stresses on all components, and proper values for all components. In a steady-state converter, the net volt-seconds across an inductor after one cycle will equal zero. Also, the charge into a capacitor will equal the charge out of a capacitor in one cycle. Therefore: I L2 D* = ' x I L1 (c)D and IL1 = 34 D * x VO * D' R (c) (c) (19) Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 Substituting IL1 into IL2 VO IL2 = R (20) The average inductor current of L2 is the average output load. VL(t) AREA 1 t (s) AREA 2 DTS TS Figure 40. Inductor Volt-Sec Balance Waveform Applying Charge balance on C1: D' (Vo ) VC1 = D (21) Since there are no DC voltages across either inductor, and capacitor C6 is connected to Vin through L1 at one end, or to ground through L2 on the other end, we can say that VC1 = VIN (22) Therefore: VIN = D' (Vo ) D (23) This verifies the original conversion ratio equation. It is important to remember that the internal switch current is equal to IL1 and IL2. During the D interval. Design the converter so that the minimum specified peak switch current limit (2.1 A) is not exceeded. 8.2.18.1.3 Steady State Analysis With Loss Elements i L1( t ) i sw iC1( t ) vC1( t ) + i D1( t ) vD1( t ) i L 2( t ) VIN i C2( t ) vL2( t ) + - + R L1 vL1( t ) + vC2( t ) vO( t ) - + R on R L2 Using inductor volt-second balance & capacitor charge balance, the following equations are derived: Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 35 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 I L2 www.ti.com VO * =R (c) and IL1 = VO * D * R x D' (c) (c) Vo = VIN (c) (24) * 1 D* D' VD R L2 * D * R ON * D 2 * R L1 * + 1+ + + (c) VO R (c) D' 2 (c) R (c) D' 2 (c) R (c) (25) Therefore: * 1 K= VD R L2 * D * R ON * D 2 * R L1 * + 1+ + + (c) VO R (c) D' 2 (c) R (c) D' 2 (c) R (c) (26) One can see that all variables are known except for the duty cycle (D). A quadratic equation is needed to solve for D. A less accurate method of determining the duty cycle is to assume efficiency, and calculate the duty cycle. VO VIN D= D *xK 1 - D (c) (27) VO * (V x K) +V O (c) IN (28) = Vin Vo Iin Io K 2.7V 3.1V 770 mA 500 mA 75% Vin Vo Iin Io K 3.3V 3.1V 600 mA 500 mA 80% Vin Vo Iin Io K 5V 3.1V 375 mA 500 mA 83% Figure 41. Efficiencies for Typical SEPIC Application 36 Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 9 Power Supply Recommendations The LM2735 device is designed to operate from an input voltage supply range from 2.7 V to 5.5 V. This input supply should be able to withstand the maximum input current and maintain a voltage above 2.7 V. In case where input supply is located farther away (more than a few inches) from the device, additional bulk capacitance may be required in addition to the ceramic bypass capacitors. 10 Layout 10.1 Layout Guidelines When planning layout, there are a few things to consider when trying to achieve a clean, regulated output. The most important consideration when completing a boost converter layout is the close coupling of the GND connections of the COUT capacitor and the LM2735 PGND pin. The GND ends should be close to one another and be connected to the GND plane with at least two through-holes. There should be a continuous ground plane on the bottom layer of a two-layer board except under the switching node island. The FB pin is a high impedance node and care should be taken to make the FB trace short to avoid noise pickup and inaccurate regulation. The feedback resistors should be placed as close as possible to the IC, with the AGND of R1 placed as close as possible to the GND (pin 5 for the WSON) of the IC. The VOUT trace to R2 should be routed away from the inductor and any other traces that are switching. High AC currents flow through the VIN, SW and VOUT traces, so they should be as short and wide as possible. However, making the traces wide increases radiated noise, so the designer must make this trade-off. Radiated noise can be decreased by choosing a shielded inductor. The remaining components should also be placed as close as possible to the IC. See Application Note AN-1229 SIMPLE SWITCHER(R) PCB Layout Guidelines (SNVA054) for further considerations and the LM2735 demo board as an example of a 4-layer layout. Below is an example of a good thermal and electrical PCB design. This is very similar to our LM2735 demonstration boards that are obtainable through the TI website. The demonstration board consists of a 2-layer PCB with a common input and output voltage application. Most of the routing is on the top layer, with the bottom layer consisting of a large ground plane. The placement of the external components satisfies the electrical considerations, and the thermal performance has been improved by adding thermal vias and a top layer DogBone. 10.1.1 WSON Package The LM2735 packaged in the 6-pin WSON: Figure 42. Internal WSON Connection For certain high power applications, the PCB land may be modified to a dog bone shape (see Figure 43). Increasing the size of ground plane, and adding thermal vias can reduce the RJA for the application. Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 37 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com Layout Guidelines (continued) COPPER PGND 1 6 SW Vin 2 5 AGND EN 3 4 FB COPPER Figure 43. PCB Dog Bone Layout 10.2 Layout Examples CIN PCB VIN PGND L1 FB 4 EN 3 AGND VIN 5 2 PGND SW 6 1 CIN COUT D1 VO Figure 44. Example of Proper PCB Layout 38 Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 Layout Examples (continued) The layout guidelines described for the LM2735 Boost-Converter are applicable to the SEPIC Converter. Figure 45 shows a proper PCB layout for a SEPIC Converter. CIN PCB VIN PGND L1 FB 4 EN 3 AGND VIN 5 2 PGND SW 6 1 CIN COUT D1 VO C6 L2 Figure 45. SEPIC PCB Layout 10.3 Thermal Considerations When designing for thermal performance, one must consider many variables: * Ambient Temperature: The surrounding maximum air temperature is fairly explanatory. As the temperature increases, the junction temperature will increase. This may not be linear though. As the surrounding air temperature increases, resistances of semiconductors, wires and traces increase. This will decrease the efficiency of the application, and more power will be converted into heat, and will increase the silicon junction temperatures further. * Forced Airflow: Forced air can drastically reduce the device junction temperature. Air flow reduces the hot spots within a design. Warm airflow is often much better than a lower ambient temperature with no airflow. * External Components: Choose components that are efficient, and you can reduce the mutual heating between devices. Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 39 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com Thermal Considerations (continued) 10.3.1 Definitions Heat energy is transferred from regions of high temperature to regions of low temperature through three basic mechanisms: radiation, conduction and convection. Radiation Electromagnetic transfer of heat between masses at different temperatures. Conduction Transfer of heat through a solid medium. Convection Transfer of heat through the medium of a fluid; typically air. Conduction & Convection will be the dominant heat transfer mechanism in most applications. RJC Thermal impedance from silicon junction to device case temperature. RJA Thermal impedance from silicon junction to ambient air temperature. CJC Thermal Delay from silicon junction to device case temperature. CCA Thermal Delay from device case to ambient air temperature. RJA & RJC These two symbols represent thermal impedances, and most data sheets contain associated values for these two symbols. The units of measurement are C/Watt. RJAis the sum of smaller thermal impedances (see Figure 46). The capacitors represent delays that are present from the time that power and its associated heat is increased or decreased from steady state in one medium until the time that the heat increase or decrease reaches steady state on the another medium. RTC - A C TC - A TA TC R TJ- CASE C TJ- CASE TJ Internal - P DISS Figure 46. Simplified Thermal Impedance Model The datasheet values for these symbols are given so that one might compare the thermal performance of one package against another. In order to achieve a comparison between packages, all other variables must be held constant in the comparison (PCB size, copper weight, thermal vias, power dissipation, VIN, VOUT, Load Current, and so forth). This does shed light on the package performance, but it would be a mistake to use these values to calculate the actual junction temperature in your application. TJ - TA R TJA = PDissipation (29) We will talk more about calculating the variables of this equation later, and how to eventually calculate a proper junction temperature with relative certainty. For now we need to define the process of calculating the junction temperature and clarify some common misconceptions. 40 Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 Thermal Considerations (continued) RJA [Variables]: * Input voltage, output voltage, output current, RDSon. * Ambient temperature and air flow. * Internal and external components power dissipation. * Package thermal limitations. * PCB variables (copper weight, thermal vias, layers component placement). It is incorrect to assume that the top case temperature is the proper temperature when calculating RJC value. The RJC value represents the thermal impedance of all six sides of a package, not just the top side. This document refers to a thermal impedance called RJC. RJC represents a thermal impedance associated with just the top case temperature. This allows the user to calculate the junction temperature with a thermal sensor connected to the top case. 10.3.2 PCB Design With Thermal Performance in Mind The PCB design is a very important step in the thermal design procedure. The LM2735 is available in three package options (5-pin SOT-23, 8-pin MSOP-PowerPAD, and 6-pin WSON). The options are electrically the same, but difference between the packages is size and thermal performance. The WSON and MSOP-PowerPAD have thermal Die Attach Pads (DAP) attached to the bottom of the packages, and are therefore capable of dissipating more heat than the SOT-23 package. It is important that the correct package for the application is chosen. A detailed thermal design procedure has been included in this data sheet. This procedure will help determine which package is correct, and common applications will be analyzed. There is one significant thermal PCB layout design consideration that contradicts a proper electrical PCB layout design consideration. This contradiction is the placement of external components that dissipate heat. The greatest external heat contributor is the external Schottky diode. It would be ideal to be able to separate by distance the LM2735 from the Schottky diode, and thereby reducing the mutual heating effect, however, this will create electrical performance issues. It is important to keep the LM2735, the output capacitor, and Schottky diode physically close to each other (see Figure 44). The electrical design considerations outweigh the thermal considerations. Other factors that influence thermal performance are thermal vias, copper weight, and number of board layers. 10.3.3 LM2735 Thermal Models Heat is dissipated from the LM2735 and other devices. The external loss elements include the Schottky diode, inductor, and loads. All loss elements will mutually increase the heat on the PCB, and therefore increase each other's temperatures. L1 I L (t) D1 VOUT (t) VIN Q1 C1 Figure 47. Thermal Schematic Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 41 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com Thermal Considerations (continued) RTCASE-AMB TCASE CTCASE-AMB RTJ-CASE CTJ-CASE INTERNAL PDISS SMALL LARGE PDISS-TOP TAMBIENT PDISS-PCB TJUNCTION RTJ-PCB CTJ-PCB DEVICE EXTERNAL PDISS RTPCB-AMB TPCB CTPCB-AMB PCB Figure 48. Associated Thermal Model 10.3.4 Calculating Efficiency, and Junction Temperature The complete LM2735 DC-DC converter efficiency () can be calculated in the following manner. POUT K= PIN or K= POUT POUT + PLOSS (30) Power loss (PLOSS) is the sum of two types of losses in the converter, switching and conduction. Conduction losses usually dominate at higher output loads, where as switching losses remain relatively fixed and dominate at lower output loads. Losses in the LM2735 device: PLOSS = PCOND + PSW + PQ 42 (31) Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 Thermal Considerations (continued) Conversion ratio of the boost converter with conduction loss elements inserted: * c * VOUT 1 1 D x VD 1 = R DCR + (D x R DSON) VIN Dc (c) VIN 1+ Dc 2R OUT (c) (32) If the loss elements are reduced to zero, the conversion ratio simplifies to: VOUT 1 = VIN Dc (33) And this is known: K VOUT = VIN Dc (34) Therefore: K = Dc VOUT VIN Dc x VD * 1 VIN = + (D x R DSON) R 1 + DCR Dc 2R OUT (c) (35) Calculations for determining the most significant power losses are discussed below. Other losses totaling less than 2% are not discussed. A simple efficiency calculation that takes into account the conduction losses is shown below: Dc x VD * 1 V IN K| R DCR + (D x R DSON) 1+ Dc 2R OUT (c) (36) The diode, NMOS switch, and inductor DCR losses are included in this calculation. Setting any loss element to zero will simplify the equation. VD is the forward voltage drop across the Schottky diode. It can be obtained from the manufacturer's Electrical Characteristics section of the data sheet. The conduction losses in the diode are calculated as follows: PDIODE = VD x IO (37) Depending on the duty cycle, this can be the single most significant power loss in the circuit. Care should be taken to choose a diode that has a low forward voltage drop. Another concern with diode selection is reverse leakage current. Depending on the ambient temperature and the reverse voltage across the diode, the current being drawn from the output to the NMOS switch during time D could be significant, this may increase losses internal to the LM2735 and reduce the overall efficiency of the application. See the data sheets of the Schottky diode manufacturer for reverse leakage specifications; and, typical applications within this data sheet for diode selections. Another significant external power loss is the conduction loss in the input inductor. The power loss within the inductor can be simplified to: PIND = IIN2RDCR (38) I 2 R * PIND = O DCR D' (c) (39) Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 43 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com Thermal Considerations (continued) The LM2735 conduction loss is mainly associated with the internal NFET: PCOND-NFET = I2SW-rms x RDSON x D (40) 'i I I sw(t) t Figure 49. LM2735 Switch Current 'i IIND Isw-rms = IIND D x 1 + 1 3 2 | IIND D PIND = IIN2 x RIND-DCR (small ripple approximation) PCOND-NFET = IIN2 x RDSON x D (41) (42) 2 I * PCOND - NFET = O x RDSON x D (c) D' (43) The value for should be equal to the resistance at the junction temperature you wish to analyze. As an example, at 125C and VIN = 5 V, RDSON = 250 m (see Typical Characteristics for value). Switching losses are also associated with the internal NMOS switch. They occur during the switch on and off transition periods, where voltages and currents overlap resulting in power loss. The simplest means to determine this loss is to empirically measuring the rise and fall times (10% to 90%) of the switch at the switch node: PSWR = 1/2(VOUT x IIN x FSW x TRISE) PSWF = 1/2(VOUT x IIN x FSW x TFALL) PSW = PSWR + PSWF (44) (45) (46) Table 2. Typical Switch-Node Rise and Fall Times VIN VOUT TRISE TFALL 3V 5V 6 nS 4 nS 5V 12 V 6 nS 5 nS 3V 12 V 7 nS 5 nS 5V 18 V 7 nS 5 nS Quiescent Power Losses: IQ is the quiescent operating current, and is typically around 4 mA. PQ = IQ x VIN 44 (47) Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 10.3.4.1 Example Efficiency Calculation Table 3. Operating Conditions PARAMETER VALUE VIN 5V VOUT 12 V IOUT 500 mA VD 0.4 V FSW 1.60 MHz IQ 4 mA TRISE 6 nS TFALL 5 nS RDSon 250 m RDCR 50 m D 0.64 IIN 1.4 A PCOND + PSW + PDIODE + PIND + PQ = PLOSS (48) Quiescent Power Losses: PQ = IQ x VIN = 20 mW (49) Switching Power Losses: PSWR = 1/2(VOUT x IIN x FSW x TRISE) 6 ns 80 mW PSWF = 1/2(VOUT x IIN x FSW x TFALL) 5 ns 70 mW PSW = PSWR + PSWF = 150 mW (50) (51) (52) Internal NFET Power Losses: RDSON = 250 m PCONDUCTION = IIN2 x D x RDSON x 305 mW (53) (54) Diode Losses: VD = 0.45 V PDIODE = VD x IIN(1-D) = 236 mW (55) (56) Inductor Power Losses: RDCR = 75 m PIND = IIN2 x RDCR = 145 mW (57) (58) Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 45 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com Total Power Losses are: Table 4. Power Loss Tabulation PARAMETER VALUE VIN 5V PARAMETER VOUT 12 V IOUT 500 mA POUT 6W VD 0.4 V PDIODE 236 mW FSW 1.6 MHz TRISE 6 nS PSWR 80 mW TFALL 5 nS PSWF 70 mW IQ 4 mA PQ 20 mW RDSon 250 m PCOND 305 mW RDCR 75 m PIND 145 mW D 0.623 86% PLOSS 856 mW PINTERNAL = PCOND + PSW = 475 mW VALUE (59) 10.3.5 Calculating RJA and RJC R TJA = TJ - TA PDissipation and R <JC = TJ - TCASE PDissipation (60) Now the internal power dissipation is known, and the junction temperature is attempted to be kept at or below 125C. The next step is to calculate the value for RJA and/or RJC. This is actually very simple to accomplish, and necessary if marginality is a possibility in regards to thermals or determining what package option is correct. The LM2735 has a thermal shutdown comparator. When the silicon reaches a temperature of 160C, the device shuts down until the temperature reduces to 150C. Knowing this, the RJA or the RJC of a specific application can be calculated. Because the junction-to-top case thermal impedance is much lower than the thermal impedance of junction to ambient air, the error in calculating RJC is lower than for RJA . However, a small thermocouple will need to be attached onto the top case of the LM2735 to obtain the RJC value. Knowing the temperature of the silicon when the device shuts down allows three of the four variables to be known. Once the thermal impedance is calculated, work backwards with the junction temperature set to 125C to determine what maximum ambient air temperature keeps the silicon below the 125C temperature. 10.3.5.1 Procedure Place the application into a thermal chamber. Sufficient power will need to be dissipated in the device so that a good thermal impedance value may be obtained. Raise the ambient air temperature until the device goes into thermal shutdown. Record the temperatures of the ambient air and/or the top case temperature of the LM2735. Calculate the thermal impedances. 46 Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 10.3.5.2 Example From Previous Calculations PDissipation = 475 mW TA at Shutdown = 139C TCase-Top at Shutdown = 155C TJ - TA TJ - TCase-Top : R <JC = R TJA = PDissipation PDissipation (61) RJA WSON = 55C/W RJC WSON = 21C/W WSON & MSOP-PowerPAD typical applications will produce RJA numbers in the range of 50C/W to 65C/W, and RJC will vary from 18C/W to 28C/W. These values are for PCB's with two and four layer boards with 0.5oz copper, and 4 to 6 thermal vias to bottom side ground plane under the DAP. For 5-pin SOT-23 package typical applications, RJA numbers will range from 80C/W to 110C/W, and RJC will vary from 50C/W to 65C/W. These values are for PCBs with 2- and 4-layer boards with 0.5-oz copper, with 2 to 4 thermal vias from GND pin to bottom layer. The following is a good rule of thumb for typical thermal impedances, and an ambient temperature maximum of 75C: if the design requires more than 400 mW internal to the LM2735 be dissipated, or there is 750 mW of total power loss in the application, TI recommends using the 6-pin WSON or the 8-pin MSOP-PowerPAD package. NOTE To use these procedures, it is important to dissipate an amount of power within the device that will indicate a true thermal impedance value. If a very small internal dissipated value is used, it can be determined that the thermal impedance calculated is abnormally high, and subject to error. The graph below shows the nonlinear relationship of internal power dissipation vs RJA. 500 450 400 350 RTJA 300 250 200 150 100 50 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 PDISS Figure 50. RJA vs Internal Dissipation for the WSON and MSOP-PowerPAD Package Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 47 LM2735 SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 www.ti.com 11 Device and Documentation Support 11.1 Device Support 11.1.1 Third-Party Products Disclaimer TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE. 11.1.2 Development Support 11.1.2.1 Custom Design With WEBENCH(R) Tools Click here to create a custom design using the LM2735 device with the WEBENCH(R) Power Designer. 1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements. 2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial. 3. Compare the generated design with other possible solutions from Texas Instruments. The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time pricing and component availability. In most cases, these actions are available: * Run electrical simulations to see important waveforms and circuit performance * Run thermal simulations to understand board thermal performance * Export customized schematic and layout into popular CAD formats * Print PDF reports for the design, and share the design with colleagues Get more information about WEBENCH tools at www.ti.com/WEBENCH. 11.2 Documentation Support 11.2.1 Related Documentation For related documentation, see the following: AN-1229 SIMPLE SWITCHER (R) PCB Layout Guidelines, SNVA054 11.3 Community Resources The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of Use. TI E2ETM Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help solve problems with fellow engineers. Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and contact information for technical support. 11.4 Trademarks PowerPAD, E2E are trademarks of Texas Instruments. WEBENCH is a registered trademark of Texas Instruments. All other trademarks are the property of their respective owners. 11.5 Electrostatic Discharge Caution These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. 48 Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 LM2735 www.ti.com SNVS485I - JUNE 2007 - REVISED SEPTEMBER 2018 11.6 Glossary SLYZ022 -- TI Glossary. This glossary lists and explains terms, acronyms, and definitions. 12 Mechanical, Packaging, and Orderable Information The following pages include mechanical, packaging, and orderable information. This information is the most current data available for the designated devices. This data is subject to change without notice and revision of this document. For browser-based versions of this data sheet, refer to the left-hand navigation. Submit Documentation Feedback Copyright (c) 2007-2018, Texas Instruments Incorporated Product Folder Links: LM2735 49 PACKAGE OPTION ADDENDUM www.ti.com 6-Feb-2020 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan Lead/Ball Finish MSL Peak Temp (2) (6) (3) Op Temp (C) Device Marking (4/5) LM2735XMF/NOPB ACTIVE SOT-23 DBV 5 1000 Green (RoHS & no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 SLEB LM2735XMFX/NOPB ACTIVE SOT-23 DBV 5 3000 Green (RoHS & no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 SLEB LM2735XMY/NOPB ACTIVE HVSSOP DGN 8 1000 Green (RoHS & no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 SRJB LM2735XSD/NOPB ACTIVE WSON NGG 6 1000 Green (RoHS & no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2735X LM2735XSDX/NOPB ACTIVE WSON NGG 6 4500 Green (RoHS & no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2735X LM2735YMF/NOPB ACTIVE SOT-23 DBV 5 1000 Green (RoHS & no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 SLFB LM2735YMFX/NOPB ACTIVE SOT-23 DBV 5 3000 Green (RoHS & no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 SLFB LM2735YMY/NOPB ACTIVE HVSSOP DGN 8 1000 Green (RoHS & no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 SRKB LM2735YSD/NOPB ACTIVE WSON NGG 6 1000 Green (RoHS & no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2735Y LM2735YSDX/NOPB ACTIVE WSON NGG 6 4500 Green (RoHS & no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 2735Y (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may reference these types of products as "Pb-Free". RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption. Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based flame retardants must also meet the <=1000ppm threshold requirement. (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. Addendum-Page 1 Samples PACKAGE OPTION ADDENDUM www.ti.com (4) 6-Feb-2020 There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Device Marking for that device. (6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish value exceeds the maximum column width. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis. OTHER QUALIFIED VERSIONS OF LM2735 : * Automotive: LM2735-Q1 NOTE: Qualified Version Definitions: * Automotive - Q100 devices qualified for high-reliability automotive applications targeting zero defects Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 6-Sep-2019 TAPE AND REEL INFORMATION *All dimensions are nominal Device LM2735XMF/NOPB Package Package Pins Type Drawing SPQ SOT-23 Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) DBV 5 1000 178.0 B0 (mm) K0 (mm) P1 (mm) 8.4 3.2 3.2 1.4 4.0 W Pin1 (mm) Quadrant 8.0 Q3 LM2735XMFX/NOPB SOT-23 DBV 5 3000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3 LM2735XMY/NOPB HVSSOP DGN 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM2735XSD/NOPB WSON NGG 6 1000 178.0 12.4 3.3 3.3 1.0 8.0 12.0 Q1 LM2735XSDX/NOPB WSON NGG 6 4500 330.0 12.4 3.3 3.3 1.0 8.0 12.0 Q1 LM2735YMF/NOPB SOT-23 DBV 5 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3 LM2735YMFX/NOPB SOT-23 DBV 5 3000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3 LM2735YMY/NOPB HVSSOP DGN 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM2735YSD/NOPB WSON NGG 6 1000 178.0 12.4 3.3 3.3 1.0 8.0 12.0 Q1 LM2735YSDX/NOPB WSON NGG 6 4500 330.0 12.4 3.3 3.3 1.0 8.0 12.0 Q1 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 6-Sep-2019 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM2735XMF/NOPB SOT-23 DBV 5 1000 210.0 185.0 35.0 LM2735XMFX/NOPB SOT-23 DBV 5 3000 210.0 185.0 35.0 LM2735XMY/NOPB HVSSOP DGN 8 1000 210.0 185.0 35.0 LM2735XSD/NOPB WSON NGG 6 1000 210.0 185.0 35.0 LM2735XSDX/NOPB WSON NGG 6 4500 367.0 367.0 35.0 LM2735YMF/NOPB SOT-23 DBV 5 1000 210.0 185.0 35.0 LM2735YMFX/NOPB SOT-23 DBV 5 3000 210.0 185.0 35.0 LM2735YMY/NOPB HVSSOP DGN 8 1000 210.0 185.0 35.0 LM2735YSD/NOPB WSON NGG 6 1000 210.0 185.0 35.0 LM2735YSDX/NOPB WSON NGG 6 4500 367.0 367.0 35.0 Pack Materials-Page 2 PACKAGE OUTLINE DBV0005A SOT-23 - 1.45 mm max height SCALE 4.000 SMALL OUTLINE TRANSISTOR C 3.0 2.6 1.75 1.45 PIN 1 INDEX AREA 1 0.1 C B A 5 2X 0.95 1.9 1.45 0.90 3.05 2.75 1.9 2 4 0.5 5X 0.3 0.2 3 (1.1) C A B 0.15 TYP 0.00 0.25 GAGE PLANE 8 TYP 0 0.22 TYP 0.08 0.6 TYP 0.3 SEATING PLANE 4214839/E 09/2019 NOTES: 1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing per ASME Y14.5M. 2. This drawing is subject to change without notice. 3. Refernce JEDEC MO-178. 4. Body dimensions do not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, or gate burrs shall not exceed 0.15 mm per side. www.ti.com EXAMPLE BOARD LAYOUT DBV0005A SOT-23 - 1.45 mm max height SMALL OUTLINE TRANSISTOR PKG 5X (1.1) 1 5 5X (0.6) SYMM (1.9) 2 2X (0.95) 3 4 (R0.05) TYP (2.6) LAND PATTERN EXAMPLE EXPOSED METAL SHOWN SCALE:15X SOLDER MASK OPENING METAL SOLDER MASK OPENING METAL UNDER SOLDER MASK EXPOSED METAL EXPOSED METAL 0.07 MIN ARROUND 0.07 MAX ARROUND NON SOLDER MASK DEFINED (PREFERRED) SOLDER MASK DEFINED SOLDER MASK DETAILS 4214839/E 09/2019 NOTES: (continued) 5. Publication IPC-7351 may have alternate designs. 6. Solder mask tolerances between and around signal pads can vary based on board fabrication site. www.ti.com EXAMPLE STENCIL DESIGN DBV0005A SOT-23 - 1.45 mm max height SMALL OUTLINE TRANSISTOR PKG 5X (1.1) 1 5 5X (0.6) SYMM (1.9) 2 2X(0.95) 4 3 (R0.05) TYP (2.6) SOLDER PASTE EXAMPLE BASED ON 0.125 mm THICK STENCIL SCALE:15X 4214839/E 09/2019 NOTES: (continued) 7. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate design recommendations. 8. Board assembly site may have different recommendations for stencil design. www.ti.com PACKAGE OUTLINE TM DGN0008A PowerPAD VSSOP - 1.1 mm max height SCALE 4.000 SMALL OUTLINE PACKAGE C 5.05 TYP 4.75 A 0.1 C SEATING PLANE PIN 1 INDEX AREA 6X 0.65 8 1 2X 3.1 2.9 NOTE 3 1.95 4 5 8X B 3.1 2.9 NOTE 4 0.38 0.25 0.13 C A B 0.23 0.13 SEE DETAIL A EXPOSED THERMAL PAD 4 5 0.25 GAGE PLANE 2.0 1.7 9 1.1 MAX 8 1 0 -8 0.15 0.05 0.7 0.4 DETAIL A A 20 1.88 1.58 TYPICAL 4218836/A 11/2019 PowerPAD is a trademark of Texas Instruments. NOTES: 1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing per ASME Y14.5M. 2. This drawing is subject to change without notice. 3. This dimension does not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, or gate burrs shall not exceed 0.15 mm per side. 4. This dimension does not include interlead flash. Interlead flash shall not exceed 0.25 mm per side. 5. Reference JEDEC registration MO-187. www.ti.com EXAMPLE BOARD LAYOUT TM DGN0008A PowerPAD VSSOP - 1.1 mm max height SMALL OUTLINE PACKAGE (2) NOTE 9 METAL COVERED BY SOLDER MASK (1.88) SOLDER MASK DEFINED PAD SYMM 8X (1.4) (R0.05) TYP 8 8X (0.45) 1 (3) NOTE 9 SYMM 9 (2) (1.22) 6X (0.65) 5 4 ( 0.2) TYP VIA (0.55) SEE DETAILS (4.4) LAND PATTERN EXAMPLE EXPOSED METAL SHOWN SCALE: 15X SOLDER MASK OPENING METAL UNDER SOLDER MASK METAL SOLDER MASK OPENING EXPOSED METAL EXPOSED METAL 0.05 MAX ALL AROUND NON-SOLDER MASK DEFINED (PREFERRED) 0.05 MIN ALL AROUND SOLDER MASK DEFINED SOLDER MASK DETAILS 15.000 4218836/A 11/2019 NOTES: (continued) 6. Publication IPC-7351 may have alternate designs. 7. Solder mask tolerances between and around signal pads can vary based on board fabrication site. 8. Vias are optional depending on application, refer to device data sheet. If any vias are implemented, refer to their locations shown on this view. It is recommended that vias under paste be filled, plugged or tented. 9. Size of metal pad may vary due to creepage requirement. www.ti.com EXAMPLE STENCIL DESIGN TM DGN0008A PowerPAD VSSOP - 1.1 mm max height SMALL OUTLINE PACKAGE (1.88) BASED ON 0.125 THICK STENCIL SYMM (R0.05) TYP 8X (1.4) 8X (0.45) 8 1 SYMM (2) BASED ON 0.125 THICK STENCIL 6X (0.65) 5 4 METAL COVERED BY SOLDER MASK (4.4) SEE TABLE FOR DIFFERENT OPENINGS FOR OTHER STENCIL THICKNESSES SOLDER PASTE EXAMPLE EXPOSED PAD 9: 100% PRINTED SOLDER COVERAGE BY AREA SCALE: 15X STENCIL THICKNESS SOLDER STENCIL OPENING 0.1 0.125 0.15 0.175 2.10 X 2.24 1.88 X 2.00 (SHOWN) 1.72 X 1.83 1.59 X 1.69 4218836/A 11/2019 NOTES: (continued) 10. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate design recommendations. 11. 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