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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

LM2735 520-kHz and 1.6-MHz Space-Efficient Boost and SEPIC DC/DC Regulator

1 Features

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-mΩNMOS 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 MSOP-

PowerPAD™ Packages

• Create a Custom Design Using the LM2735 With

WEBENCH®Power Designer

2 Applications

• 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

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-by-

pulse current limit, and thermal shutdown.

Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)

LM2735 WSON (6) 3.00 mm × 3.00 mm

SOT-23 (5) 1.60 mm × 2.90 mm

MSOP PowerPAD (8) 3.00 mm × 3.00 mm

(1) For all available packages, see the orderable addendum at

the end of the data sheet.

space Typical Boost Application Circuit Efficiency vs Load Current VO= 12 V

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Table of Contents

1 Features.................................................................. 1

2 Applications ........................................................... 1

3 Description............................................................. 1

4 Revision History..................................................... 2

5 Pin Configuration and Functions......................... 3

6 Specifications......................................................... 4

6.1 Absolute Maximum Ratings ...................................... 4

6.2 ESD Ratings: LM2735 .............................................. 4

6.3 Recommended Operating Conditions....................... 4

6.4 Thermal Information.................................................. 4

6.5 Electrical Characteristics........................................... 5

6.6 Typical Characteristics.............................................. 7

7 Detailed Description.............................................. 9

7.1 Overview................................................................... 9

7.2 Functional Block Diagram....................................... 11

7.3 Feature Description................................................. 11

7.4 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 Device Support...................................................... 48

11.2 Documentation Support ........................................ 48

11.3 Community Resources.......................................... 48

11.4 Trademarks........................................................... 48

11.5 Electrostatic Discharge Caution............................ 48

11.6 Glossary................................................................ 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 Page

• Added bullet to Applications list regarding automotive device LM2735-Q1 .......................................................................... 1

Changes from Revision G (August 2015) to Revision H Page

• Changed VFB Feedback Test Conditions from "TJ= –40°C to 125°C" To "TJ= 0°C to 125°C" for the SOT-23,

WSON, and MSOP-PowerPAD devices................................................................................................................................. 5

Changes from Revision F (April 2013) to Revision G 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 layout of National Data Sheet to TI format ........................................................................................................... 33

AGND

VIN

PGND

AGND

VIN

PGND

8NCNC

4EN

GND

VIN

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5 Pin Configuration and Functions

DBV Package

5-Pin SOT-23

Top View

NGG Package

6-Pin WSON

Top View

DGN Package

8-Pin MSOP-PowerPAD

Top View

Pin Functions

PIN I/O DESCRIPTION

NAME SOT-23 WSON MSOP-

PowerPAD

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 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.

NC — — 1, 8 — No Connect

PGND — 1 2 PWR Power ground pin. Place PGND and output capacitor GND close

together.

SW 1 6 7 O Output switch. Connect to the inductor, output diode.

VIN 5 2 3 PWR Supply voltage for power stage, and input supply voltage.

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(1) If Military/Aerospace specified devices are required, contact the Texas Instruments Sales Office/ Distributors for availability and

specifications.

(2) Thermal shutdown will occur if the junction temperature exceeds the maximum junction temperature of the device.

6 Specifications

6.1 Absolute Maximum Ratings

See(1)

MIN MAX UNIT

VIN –0.5 7 V

SW Voltage –0.5 26.5 V

FB Voltage –0.5 3 V

EN Voltage –0.5 7 V

Junction temperature(2) 150 °C

Soldering information, infrared/convection reflow (15 s) 220 °C

Storage Temperature –65 150 °C

(1) 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.

(2) The human body model is a 100-pF capacitor discharged through a 1.5-kΩresistor into each pin.

(3) 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.

6.2 ESD Ratings: LM2735 VALUE UNIT

V(ESD) Electrostatic discharge Human body model (HBM), per ANSI/ESDA/JEDEC JS-001(1)(2) ±2000 V

Charged device model (CDM), per JEDEC specification JESD22-

C101(3) ±1000

(1) Do not allow this pin to float or be greater than VIN + 0.3 V.

6.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted) MIN NOM MAX UNIT

VIN 2.7 5.5 V

VSW 3 24 V

VEN(1) 0 VIN V

Junction Temperature Range –40 125 °C

Power Dissipation (Internal) SOT-23 400 mW

(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application

report.

(2) Applies for packages soldered directly onto a 3” × 3” PC board with 2-oz. copper on 4 layers in still air.

6.4 Thermal Information

THERMAL METRIC(1)

LM2735

UNIT

NGG (WSON) DBV (SOT-23) DGN (MSOP-

PowerPAD)

6 PINS 5 PINS 8 PINS

RθJA Junction-to-ambient thermal resistance(2) 54.9 164.2 59 °C/W

RθJC(top) Junction-to-case (top) thermal resistance(2) 50.9 115.3 51.2 °C/W

RθJB Junction-to-board thermal resistance 29.3 27 35.8 °C/W

ψJT Junction-to-top characterization parameter 0.7 12.8 2.7 °C/W

ψJB Junction-to-board characterization parameter 29.4 26.5 35.6 °C/W

RθJC(bot) Junction-to-case (bottom) thermal resistance 9.3 N/A 7.3 °C/W

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6.5 Electrical Characteristics

Limits are for TJ= 25°C. Minimum and Maximum limits are specified through test, design, or statistical correlation. Typical

values represent the most likely parametric norm at TJ= 25°C, and are provided for reference purposes only. VIN = 5 V unless

otherwise indicated under the Conditions column.

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

VFB Feedback Voltage

–40°C ≤to TJ≤125°C (SOT-23) TJ= 25°C 1.255

TJ= –40°C to 125°C 1.23 1.28

0°C ≤to TJ≤125°C (SOT-23) TJ= 25°C 1.255

TJ= 0°C to 125°C 1.236 1.274

–40°C ≤to TJ≤125°C (WSON) TJ= 25°C 1.255

TJ= –40°C to 125°C 1.225 1.285

0°C ≤to TJ≤125°C (WSON) TJ= 25°C 1.255

TJ= 0°C to 125°C 1.229 1.281

–40°C ≤to TJ≤125°C

(MSOP-PowerPAD) TJ= 25°C 1.255

TJ= –40°C to 125°C 1.22 1.29

0°C ≤to TJ≤125°C (MSOP-

PowerPAD) TJ= 25°C 1.255

TJ= 0°C to 125°C 1.23 1.28

ΔVFB/VIN Feedback Voltage Line

Regulation VIN = 2.7 V to 5.5 V 0.06 %/V

IFB Feedback Input Bias

Current TJ= 25°C 0.1 µA

TJ= –40°C to 125°C 1

FSW Switching Frequency LM2735-X TJ= 25°C 1600

kHz

TJ= –40°C to 125°C 1200 2000

LM2735-Y TJ= 25°C 520

TJ= –40°C to 125°C 360 680

DMAX Maximum Duty Cycle LM2735-X TJ= 25°C 96%

TJ= –40°C to 125°C 88%

LM2735-Y TJ= 25°C 99%

TJ= –40°C to 125°C 91%

DMIN Minimum Duty Cycle LM2735-X 5%

LM2735-Y 2%

RDS(ON) Switch ON-Resistance SOT-23 and MSOP-PowerPAD TJ= 25°C 170

mΩ

TJ= –40°C to 125°C 330

WSON TJ= 25°C 190

TJ= –40°C to 125°C 350

ICL Switch Current Limit TJ= 25°C 3 A

TJ= –40°C to 125°C 2.1

SS Soft Start 4 ms

Quiescent Current

(switching)

LM2735-X TJ= 25°C 7

TJ= –40°C to 125°C 11

LM2735-Y TJ= 25°C 3.4

TJ= –40°C to 125°C 7

Quiescent Current

(shutdown) All Options VEN = 0 V 80 nA

UVLO Undervoltage Lockout VIN Rising TJ= 25°C 2.3

TJ= –40°C to 125°C 2.65

VIN Falling TJ= 25°C 1.9

TJ= –40°C to 125°C 1.7

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Electrical Characteristics (continued)

Limits are for TJ= 25°C. Minimum and Maximum limits are specified through test, design, or statistical correlation. Typical

values represent the most likely parametric norm at TJ= 25°C, and are provided for reference purposes only. VIN = 5 V unless

otherwise indicated under the Conditions column.

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

(1) Do not allow this pin to float or be greater than VIN + 0.3 V.

(2) Thermal shutdown will occur if the junction temperature exceeds the maximum junction temperature of the device.

VEN_TH

Shutdown Threshold

Voltage See(1), TJ= –40°C to 125°C 0.4 V

Enable Threshold

Voltage See(1), TJ= –40°C to 125°C 1.8

I-SW Switch Leakage VSW = 24 V 1 µA

I-EN Enable Pin Current Sink/Source 100 nA

TSD

Thermal Shutdown

Temperature(2) 160 °C

Thermal Shutdown

Hysteresis 10

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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

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Typical Characteristics (continued)

VO= 20 V Figure 7. LM2735X Efficiency vs Load Current VO= 20 V Figure 8. LM2735Y Efficiency vs Load Current

VO= 12 V Figure 9. LM2735X Efficiency vs Load Current VO= 12 V Figure 10. LM2735Y Efficiency vs Load Current

Figure 11. Output Voltage Load Regulation Figure 12. Output Voltage Line Regulation

Control ( )

( )

I( )

( )

tSW

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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-by-

pulse 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. ILis 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 .

Figure 13. Simplified Schematic

DO VV +

( )

tsw

VIN -VOUT -D

( )

tDIODE

( )

tCapacitor

( )

tOUT

OUT

-i

( )

iOUT

-i

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Overview (continued)

Figure 14. Typical Waveforms

1.6 MHz S



EN VIN

ThermalSHDN

ILIMIT

NMOS

UVLO = 2.3V

ISENSE-AMP

Internal

Compensation

Soft-Start

Corrective - Ramp Oscillator

Control Logic

VREF = 1.255V

GND

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7.2 Functional Block Diagram

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 160°C. After thermal shutdown occurs, the output switch does not turn on until the junction temperature

drops to approximately 150°C.

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.

10 kHz5 kHzo

( )

R2xCf

FCFZERO-

REF

§OUT

R1¸

- x 1

10 100 1k 10k 100k 1M

FREQUENCY

-80

-60

-40

-20

-180

-90

180

RHP-Zero

Ext (Cf)

gm-Pole

RC-Pole

Vi = 5V

Vo = 12V

Io = 500 mA

Co = 10 mF

Lo = 5 mH

Ext (Cf)-Pole

gm-zero

-Zero

D = 0.625

Cf = 220 pF

Fz-cf = 8 kHz

RHP-Zero = 107 kHz

Fp-rc = 660 Hz

Fp-cf = 77 kHz

10 100 1k 10k 100k 1M

FREQUENCY

-80

-60

-40

-20

-180

-90

180

RHP-Zero

gm-Zero

gm-Pole

RC-Pole

Vi = 5V

Vo = 12V

Io = 500 mA

Co = 10 PF

Lo = 5 PH

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Feature Description (continued)

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.

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.

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.

(2)

=( ) RLoad

Lx2S

RHPZERO

=F CFPOLE-2S((R1 R2) x C3)

( )

R2xC3

FCFZERO-

LOAD

(RLoadCOUT)2S

FRCP-

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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:

(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:

Figure 17. Setting External Pole-Zero

(5)

There is an associated pole with the zero that was created in the above equation.

(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.

(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.

GND

Vin SW

12V

LOAD

VIN

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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 µA 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

Figure 18. LM2735X (1.6 MHz): VIN =5V,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.

VOUT

VIN

D = VOUT -IN

OUT

-D111

VOUT

VIN ¸

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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 µF, 6.3 V, X5R TDK C2012X5R0J226M

C2 Output Capacitor 10 µF, 25 V, X5R TDK C3216X5R1E106M

C3 Comp Capacitor 330 pF TDK C1608X5R1H331K

D1, Catch Diode 0.4 VfSchottky 1 A, 20 VRST STPS120M

L1 15 µH 1.5 A Coilcraft MSS5131-153ML

R1 10.2 kΩ, 1% Vishay CRCW06031022F

R2 86.6 kΩ, 1% Vishay CRCW06038662F

R3 100 kΩ, 1% Vishay CRCW06031003F

8.2.1.2.1 Custom Design With WEBENCH® Tools

Click here to create a custom design using the LM2735 device with the WEBENCH® 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):

(8)

Therefore:

(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:

where

•ηequals 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.

L = VIN

2 x 'iLx DTS

§¸

=2L

ÂixS

VIN

'i2 L

DTS¸

( )

VIN VV OUT

IN -

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Figure 19. Inductor Current

(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.

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 +ΔIL(13)

or ILpk = IOUT / D' + ΔIL(14)

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 µF to 44 µF 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 (2πfL) 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.

REF

§OUT

R1¸

- x 1

LOAD

=ESRLOUT RÂIÂVxxx OUTLoadSW CRF2 x

OUT DV

LM2735

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Product Folder Links: LM2735

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):

(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 µF 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.

Figure 20. Setting Vout

A good value for R1 is 10 kΩ.

(16)

GND

Vin SW

12V

LOAD

VIN

LM2735

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8.2.1.3 Application Curves

Vin = 3.3 V Vout = 12 V

Figure 21. LM2735X Typical Startup Waveform

Vin = 5 V Vout = 12 V

Figure 22. LM2735X Typical Startup Waveform

8.2.2 LM2735Y SOT-23 Design Example 2

Figure 23. LM2735Y (520 kHz): VIN =5V,VOUT = 12 V at 350 mA

PART ID PART VALUE MANUFACTURER PART NUMBER

U1 2.1-A Boost Regulator TI LM2735YMF

C1, Input Capacitor 22 µF, 6.3 V, X5R TDK C2012X5R0J226M

C2 Output Capacitor 10 µF, 25 V, X5R TDK C3216X5R1E106M

C3 Comp Capacitor 330 pF TDK C1608X5R1H331K

D1, Catch Diode 0.4 VfSchottky 1 A, 20 VRST STPS120M

L1 33 µH 1.5 A Coilcraft DS3316P-333ML

R1 10.2 kΩ, 1% Vishay CRCW06031022F

R2 86.6 kΩ, 1% Vishay CRCW06038662F

R3 100 kΩ, 1% Vishay CRCW06031003F

LM2735

CLOAD

LM2735

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Product Folder Links: LM2735

8.2.3 LM2735X WSON Design Example 3

Figure 24. LM2735X (1.6 MHz): VIN = 3.3 V, VOUT = 12 V at 350 mA

PART ID PART VALUE MANUFACTURER PART NUMBER

U1 2.1-A Boost Regulator TI LM2735XSD

C1 Input Capacitor 22 µF, 6.3 V, X5R TDK C2012X5R0J226M

C2 Input Capacitor No Load

C3 Output Capacitor 10 µF, 25 V, X5R TDK C3216X5R1E106M

C4 Output Capacitor No Load

C5 Comp Capacitor 330 pF TDK C1608X5R1H331K

D1, Catch Diode 0.4 VfSchottky 1 A, 20 VRST STPS120M

L1 6.8 µH 2 A Coilcraft DO1813H-682ML

R1 10.2 kΩ, 1% Vishay CRCW06031022F

R2 86.6 kΩ, 1% Vishay CRCW06038662F

R3 100 kΩ, 1% Vishay CRCW06031003F

LM2735

CLOAD

LM2735

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Product Folder Links: LM2735

8.2.4 LM2735Y WSON Design Example 4

Figure 25. 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 LM2735YSD

C1 Input Capacitor 22 µF, 6.3 V, X5R TDK C2012X5R0J226M

C2 Input Capacitor No Load

C3 Output Capacitor 10 µF, 25 V, X5R TDK C3216X5R1E106M

C4 Output Capacitor No Load

C5 Comp Capacitor 330 pF TDK C1608X5R1H331K

D1, Catch Diode 0.4 VfSchottky 1 A, 20 VRST STPS120M

L1 15 µH 2 A Coilcraft MSS5131-153ML

R1 10.2 kΩ, 1% Vishay CRCW06031022F

R2 86.6 kΩ, 1% Vishay CRCW06038662F

R3 100 kΩ, 1% Vishay CRCW06031003F

LOAD

LM2735

AGND

VIN

PGND

LM2735

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8.2.5 LM2735Y MSOP-PowerPAD Design Example 5

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 µF, 6.3 V, X5R TDK C2012X5R0J226M

C2 Input Capacitor No Load

C3 Output Capacitor 10 µF, 25 V, X5R TDK C3216X5R1E106M

C4 Output Capacitor No Load

C5 Comp Capacitor 330 pF TDK C1608X5R1H331K

D1, Catch Diode 0.4 VfSchottky 1 A, 20 VRST STPS120M

L1 15 µH 1.5 A Coilcraft MSS5131-153ML

R1 10.2 kΩ, 1% Vishay CRCW06031022F

R2 86.6 kΩ, 1% Vishay CRCW06038662F

R3 100 kΩ, 1% Vishay CRCW06031003F

GND

Vin SW

LOAD

VIN

SHDN

LM2735

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Product Folder Links: LM2735

8.2.6 LM2735X SOT-23 Design Example 6

Figure 27. LM2735X (1.6 MHz): VIN =3V,VOUT = 5 V at 500 mA

PART ID PART VALUE MANUFACTURER PART NUMBER

U1 2.1-A Boost Regulator TI LM2735XMF

C1, Input Capacitor 10 µF, 6.3 V, X5R TDK C2012X5R0J106K

C2, Output Capacitor 10 µF, 6.3 V, X5R TDK C2012X5R0J106K

C3 Comp Capacitor 1000 pF TDK C1608X5R1H102K

D1, Catch Diode 0.4 VfSchottky 1 A, 20 VRST STPS120M

L1 10 µH 1.2 A Coilcraft DO1608C-103ML

R1 10.0 kΩ, 1% Vishay CRCW08051002F

R2 30.1 kΩ, 1% Vishay CRCW08053012F

R3 100 kΩ, 1% Vishay CRCW06031003F

GND

Vin SW

LOAD

VIN

SHDN

LM2735

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8.2.7 LM2735Y SOT-23 Design Example 7

Figure 28. LM2735Y (520 kHz): VIN =3V,VOUT = 5 V at 750 mA

PART ID PART VALUE MANUFACTURER PART NUMBER

U1 2.1-A Boost Regulator TI LM2735YMF

C1 Input Capacitor 22 µF, 6.3 V, X5R TDK C2012X5R0J226M

C2 Output Capacitor 22 µF, 6.3 V, X5R TDK C2012X5R0J226M

C3 Comp Capacitor 1000 pF TDK C1608X5R1H102K

D1, Catch Diode 0.4 VfSchottky 1 A, 20 VRST STPS120M

L1 22 µH 1.2 A Coilcraft MSS5131-223ML

R1 10.0 kΩ, 1% Vishay CRCW08051002F

R2 30.1 kΩ, 1% Vishay CRCW08053012F

R3 100 kΩ, 1% Vishay CRCW06031003F

GND

Vin SW

20V

LOAD

VIN

SHDN

LM2735

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Product Folder Links: LM2735

8.2.8 LM2735X SOT-23 Design Example 8

Figure 29. LM2735X (1.6 MHz): VIN = 3.3 V, Vout = 20 V at 100 mA

PART ID PART VALUE MANUFACTURER PART NUMBER

U1 2.1-A Boost Regulator TI LM2735XMF

C1, Input Capacitor 22 µF, 6.3 V, X5R TDK C2012X5R0J226M

C2, Output Capacitor 4.7 µF, 25 V, X5R TDK C3216X5R1E475K

C3 Comp Capacitor 470 pF TDK C1608X5R1H471K

D1, Catch Diode 0.4 VfSchottky 500 mA, 30 VRVishay MBR0530

L1 10 µH 1.2 A Coilcraft DO1608C-103ML

R1 10.0 kΩ, 1% Vishay CRCW06031002F

R2 150 kΩ, 1% Vishay CRCW06031503F

R3 100 kΩ, 1% Vishay CRCW06031003F

GND

Vin SW

20V

LOAD

VIN

SHDN

LM2735

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Product Folder Links: LM2735

8.2.9 LM2735Y SOT-23 Design Example 9

Figure 30. LM2735Y (520 kHz): VIN = 3.3 V, VOUT = 20 V at 100 mA

PART ID PART VALUE MANUFACTURER PART NUMBER

U1 2.1-A Boost Regulator TI LM2735YMF

C1 Input Capacitor 22 µF, 6.3 V, X5R TDK C2012X5R0J226M

C2 Output Capacitor 10 µF, 25 V, X5R TDK C3216X5R1E106M

C3 Comp Capacitor 470 pF TDK C1608X5R1H471K

D1, Catch Diode 0.4 VfSchottky 500 mA, 30 VRVishay MBR0530

L1 33 µH 1.5 A Coilcraft DS3316P-333ML

R1 10.0 kΩ, 1% Vishay CRCW06031002F

R2 150.0 kΩ, 1% Vishay CRCW06031503F

R3 100 kΩ, 1% Vishay CRCW06031003F

LM2735

CLOAD

LM2735

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8.2.10 LM2735X WSON Design Example 10

Figure 31. LM2735X (1.6 MHz): VIN = 3.3 V, VOUT = 20 V at 150 mA

PART ID PART VALUE MANUFACTURER PART NUMBER

U1 2.1-A Boost Regulator TI LM2735XSD

C1 Input Capacitor 22 µF, 6.3 V, X5R TDK C2012X5R0J226M

C2 Input Capacitor 22 µF, 6.3 V, X5R TDK C2012X5R0J226M

C3 Output Capacitor 10 µF, 25 V, X5R TDK C3216X5R1E106M

C4 Output Capacitor No Load

C5 Comp Capacitor 470 pF TDK C1608X5R1H471K

D1, Catch Diode 0.4 VfSchottky 500 mA, 30 VRVishay MBR0530

L1 8.2 µH 2 A Coilcraft DO1813H-822ML

R1 10.0 kΩ, 1% Vishay CRCW06031002F

R2 150 kΩ, 1% Vishay CRCW06031503F

R3 100 kΩ, 1% Vishay CRCW06031003F

LM2735

CLOAD

LM2735

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Product Folder Links: LM2735

8.2.11 LM2735Y WSON Design Example 11

Figure 32. LM2735Y (520 kHz): VIN = 3.3 V, VOUT = 20 V at 150 mA

PART ID PART VALUE MANUFACTURER PART NUMBER

U1 2.1-A Boost Regulator TI LM2735YSD

C1 Input Capacitor 10 µF, 6.3 V, X5R TDK C2012X5R0J106K

C2 Input Capacitor 10 µF, 6.3 V, X5R TDK C2012X5R0J106K

C3 Output Capacitor 10 µF, 25 V, X5R TDK C3216X5R1E106M

C4 Output Capacitor No Load

C5 Comp Capacitor 470 pF TDK C1608X5R1H471K

D1, Catch Diode 0.4 VfSchottky 500 mA, 30 VRVishay MBR0530

L1 22 µH 1.5 A Coilcraft DS3316P-223ML

R1 10.0 kΩ, 1% Vishay CRCW06031002F

R2 150 kΩ, 1% Vishay CRCW06031503F

R3 100 kΩ, 1% Vishay CRCW06031003F

VIN L1D1

C1C2

C5C4

LM2735

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Product Folder Links: LM2735

8.2.12 LM2735X WSON SEPIC Design Example 12

Figure 33. LM2735X (1.6 MHz): VIN =2.7V-5V,VOUT = 3.3 V at 500 mA

PART ID PART VALUE MANUFACTURER PART NUMBER

U1 2.1-A Boost Regulator TI LM2735XSD

C1 Input Capacitor 22 µF, 6.3 V, X5R TDK C2012X5R0J226M

C2 Input Capacitor No Load

C3 Output Capacitor 10 µF, 25 V, X5R TDK C3216X5R1E106M

C4 Output Capacitor No Load

C5 Comp Capacitor 2200 pF TDK C1608X5R1H222K

C6 2.2 µF 16 V TDK C2012X5R1C225K

D1, Catch Diode 0.4 VfSchottky 1 A, 20 VRST STPS120M

L1 6.8 µH Coilcraft DO1608C-682ML

L2 6.8 µH Coilcraft DO1608C-682ML

R1 10.2 kΩ, 1% Vishay CRCW06031002F

R2 16.5 kΩ, 1% Vishay CRCW06031652F

R3 100 kΩ, 1% Vishay CRCW06031003F

LOAD

LM2735

AGND

VIN

PGND

LM2735

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Product Folder Links: LM2735

8.2.13 LM2735Y MSOP-PowerPAD SEPIC Design Example 13

Figure 34. LM2735Y (520 kHz): VIN =2.7V-5V,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 µF, 6.3 V, X5R TDK C2012X5R0J226M

C2 Input Capacitor No Load

C3 Output Capacitor 10 µF, 25 V, X5R TDK C3216X5R1E106M

C4 Output Capacitor No Load

C5 Comp Capacitor 2200 pF TDK C1608X5R1H222K

C6 2.2 µF 16 V TDK C2012X5R1C225K

D1, Catch Diode 0.4 VfSchottky 1 A, 20 VRST STPS120M

L1 15 µH 1.5 A Coilcraft MSS5131-153ML

L2 15 µH 1.5 A Coilcraft MSS5131-153ML

R1 10.2 kΩ, 1% Vishay CRCW06031002F

R2 16.5 kΩ, 1% Vishay CRCW06031652F

R3 100 kΩ, 1% Vishay CRCW06031003F

Vin SW

SHDN

Vin

CTRLDIM-

LM2735

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Product Folder Links: LM2735

8.2.14 LM2735X SOT-23 LED Design Example 14

Figure 35. LM2735X (1.6 MHz): VIN =2.7V-5V,VOUT = 20 V at 50 mA

PART ID PART VALUE MANUFACTURER PART NUMBER

U1 2.1-A Boost Regulator TI LM2735XMF

C1 Input Capacitor 22 µF, 6.3 V, X5R TDK C2012X5R0J226M

C2 Output Capacitor 4.7 µF, 25 V, X5R TDK C3216JB1E475K

D1, Catch Diode 0.4 VfSchottky 500 mA, 30 VRVishay MBR0530

L1 15 µH 1.5 A Coilcraft MSS5131-153ML

R1 25.5 Ω, 1% Vishay CRCW080525R5F

R2 100 Ω, 1% Vishay CRCW08051000F

R3 100 kΩ, 1% Vishay CRCW06031003F

LM2735

LOAD

12V

LM2735

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Product Folder Links: LM2735

8.2.15 LM2735Y WSON FlyBack Design Example 15

Figure 36. LM2735Y (520 kHz): VIN =5V,VOUT = ±12 V 150 mA

PART ID PART VALUE MANUFACTURER PART NUMBER

U1 2.1-A Boost Regulator TI LM2735YSD

C1 Input Capacitor 22 µF, 6.3 V, X5R TDK C2012X5R0J226M

C2 Output Capacitor 10 µF, 25 V, X5R TDK C3216X5R1E106M

C3 Output Capacitor 10 µF, 25 V, X5R TDK C3216X5R1E106M

Cf Comp Capacitor 330 pF TDK C1608X5R1H331K

D1, D2 Catch Diode 0.4 VfSchottky 500 mA, 30 VRVishay MBR0530

R1 10.0 kΩ, 1% Vishay CRCW06031002F

R2 86.6 kΩ, 1% Vishay CRCW06038662F

R3 100 kΩ, 1% Vishay CRCW06031003F

EN LM2735

VPWR

LM2735

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Product Folder Links: LM2735

8.2.16 LM2735X SOT-23 LED Design Example 16 VRAIL > 5.5 V Application

Figure 37. LM2735X (1.6 MHz): VPWR =9V,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 µF, 6.3 V, X5R TDK C2012X5R0J106K

C2, Output Capacitor 10 µF, 25 V, X5R TDK C3216X5R1E106M

C3 VIN Cap 0.1 µF, 6.3 V, X5R TDK C2012X5R0J104K

C4 Comp Capacitor 1000 pF TDK C1608X5R1H102K

D1, Catch Diode 0.4 VfSchottky 1 A, 20 VRST STPS120M

D2 3.3-V Zener, SOT-23 Diodes Inc BZX84C3V3

L1 6.8 µH 2 A Coilcraft DO1813H-682ML

R1 10.0 kΩ, 1% Vishay CRCW08051002F

R2 86.6 kΩ, 1% Vishay CRCW08058662F

R3 100 kΩ, 1% Vishay CRCW06031003F

R4 499 Ω, 1% Vishay CRCW06034991F

VPWR

VIN

LM2735

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Product Folder Links: LM2735

8.2.17 LM2735X SOT-23 LED Design Example 17 Two-Input Voltage Rail Application

Figure 38. LM2735X (1.6 MHz): VPWR =9Vin=2.7V-5.5V,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 µF, 6.3 V, X5R TDK C2012X5R0J106K

C2, Output Capacitor 10 µF, 25 V, X5R TDK C3216X5R1E106M

C3 VIN Capacitor 0.1 µF, 6.3 V, X5R TDK C2012X5R0J104K

C4 Comp Capacitor 1000 pF TDK C1608X5R1H102K

D1, Catch Diode 0.4 VfSchottky 1 A, 20 VRST STPS120M

L1 6.8 µH 2 A Coilcraft DO1813H-682ML

R1 10.0 kΩ, 1% Vishay CRCW08051002F

R2 86.6 kΩ, 1% Vishay CRCW08058662F

R3 100 kΩ, 1% Vishay CRCW06031003F

=R¸

§D

D'¸

IL1

and

IxL1

D¸

D = O

V + IN

VIN =D'

VIN L1D1

C1C2

C5C4

LM2735

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Product Folder Links: LM2735

8.2.18 SEPIC Converter

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:

(17)

Therefore:

(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:

(19)

i)t(

vL1( )

i)t(

vC1( )

vD1( )

vL2( )

i)t(

vC2( )

vO( )

i)t(

=( )

VIN

C1 =( )

AREA

( )

(s)

L2 =

LM2735

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Product Folder Links: LM2735

Substituting IL1 into IL2

(20)

The average inductor current of L2 is the average output load.

Figure 40. Inductor Volt-Sec Balance Waveform

Applying Charge balance on C1:

(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:

(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

Using inductor volt-second balance & capacitor charge balance, the following equations are derived:

Vin

Iin

2.7V

3.1V

770 mA

500 mA

75%

Vin

Iin

3.3V

3.1V

600 mA

500 mA

80%

Vin

Iin

3.1V

375 mA

500 mA

83%

D¸

§(VIN x K)+VO

VIN =1 - D

Dx K

+ + ¸

§R

RL1

§D2

§R

RON¸

§D

1+ +¸

RL2

K=

+ + ¸

RL1

§D2

RON¸

§D

1+ +¸

RL2

§D

VIN D'

IL1

and

D¸

R¸

IR¸

LM2735

SNVS485I –JUNE 2007–REVISED SEPTEMBER 2018

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Product Folder Links: LM2735

(24)

(25)

Therefore:

(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.

(27)

(28)

Figure 41. Efficiencies for Typical SEPIC Application

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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® 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 Dog-

Bone.

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 RθJA for the application.

VIN

PGND

AGND

VIN

PCB

PGND

COUT

CIN

Vin

AGND

PGND

COPPER

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Layout Guidelines (continued)

Figure 43. PCB Dog Bone Layout

10.2 Layout Examples

Figure 44. Example of Proper PCB Layout

VIN

PGND

AGND

VIN

PCB

PGND

COUT

CIN

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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.

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.

TJA

RPnDissipatio

-A

Internal

DISS

P-

TC-

RCASE

TJ-CCASE

TJ-

TC-

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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.

RθJC Thermal impedance from silicon junction to device case temperature.

RθJA Thermal impedance from silicon junction to ambient air temperature.

CθJC Thermal Delay from silicon junction to device case temperature.

CθCA Thermal Delay from device case to ambient air temperature.

RθJA & RθJC These two symbols represent thermal impedances, and most data sheets contain associated

values for these two symbols. The units of measurement are °C/Watt.

RθJAis 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.

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.

(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.

( )

tOUT

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Thermal Considerations (continued)

RθJA [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 RθJC value.

The RθJC 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 RψJC. RψJC 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.

Figure 47. Thermal Schematic

K=+LOSSOUT PP OUT

K=IN

OUT

PDISS-TOP

INTERNAL SMALL

LARGE

PCB

DEVICE

PDISS-PCB

PDISS

TJUNCTION

TAMBIENT

CTJ-PCB

CTJ-CASE

RTJ-PCB

RTJ-CASE

CTCASE-AMB

TCASE

EXTERNAL

PDISS

TPCB

RTPCB-AMB

CTPCB-AMB

RTCASE-AMB

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Thermal Considerations (continued)

Figure 48. Associated Thermal Model

10.3.4 Calculating Efficiency, and Junction Temperature

The complete LM2735 DC-DC converter efficiency (η) can be calculated in the following manner.

(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(31)

=RDCR

O¸

PIND

R¸

+)(

DCR

cOUT

+1 DSON

x RD

-1

K|

R¸

+)(

DCR

cOUT

+1 DSON

x RD

-1

DOUT

K=

OUT

R¸

+)(

DCR

cOUT

+1 DSON

x RD

-1 ¸

OUT

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Thermal Considerations (continued)

Conversion ratio of the boost converter with conduction loss elements inserted:

(32)

If the loss elements are reduced to zero, the conversion ratio simplifies to:

(33)

And this is known:

(34)

Therefore:

(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:

(36)

The diode, NMOS switch, and inductor DCR losses are included in this calculation. Setting any loss element to

zero will simplify the equation.

VDis 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× 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)

(39)

2xx

=RDSON

PNFET-COND

Isw-rms = IIND D1 + 'i

IIND

x IIND

PIND = IIN2 x RIND-DCR

'iI

I( )

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Thermal Considerations (continued)

The LM2735 conduction loss is mainly associated with the internal NFET:

PCOND-NFET = I2SW-rms × RDSON × D (40)

Figure 49. LM2735 Switch Current

(small ripple approximation) (41)

PCOND-NFET = IIN2× RDSON × D (42)

(43)

The value for should be equal to the resistance at the junction temperature you wish to analyze. As an example,

at 125°C and VIN =5V,RDSON = 250 mΩ(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 × IIN × FSW × TRISE) (44)

PSWF = 1/2(VOUT × IIN × FSW × TFALL) (45)

PSW = PSWR + PSWF (46)

Table 2. Typical Switch-Node Rise and Fall Times

VIN VOUT TRISE TFALL

3 V 5 V 6 nS 4 nS

5 V 12 V 6 nS 5 nS

3 V 12 V 7 nS 5 nS

5 V 18 V 7 nS 5 nS

Quiescent Power Losses:

IQis the quiescent operating current, and is typically around 4 mA.

PQ= IQx VIN (47)

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10.3.4.1 Example Efficiency Calculation

Table 3. Operating Conditions

PARAMETER VALUE

VIN 5 V

VOUT 12 V

IOUT 500 mA

VD0.4 V

FSW 1.60 MHz

IQ4 mA

TRISE 6 nS

TFALL 5 nS

RDSon 250 mΩ

RDCR 50 mΩ

D0.64

IIN 1.4 A

ΣPCOND + PSW + PDIODE + PIND + PQ= PLOSS (48)

Quiescent Power Losses:

PQ= IQ× VIN = 20 mW (49)

Switching Power Losses:

PSWR = 1/2(VOUT × IIN × FSW × TRISE)≊6ns≊80 mW (50)

PSWF = 1/2(VOUT × IIN × FSW × TFALL)≊5ns≊70 mW (51)

PSW = PSWR + PSWF = 150 mW (52)

Internal NFET Power Losses:

RDSON = 250 mΩ(53)

PCONDUCTION = IIN2× D × RDSON × 305 mW (54)

Diode Losses:

VD= 0.45 V (55)

PDIODE = VD× IIN(1–D) = 236 mW (56)

Inductor Power Losses:

RDCR = 75 mΩ(57)

PIND = IIN2× RDCR = 145 mW (58)

<JC

RPnDissipatio

-CASE

and

TJA

RPnDissipatio

-A

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Total Power Losses are:

Table 4. Power Loss Tabulation

PARAMETER VALUE PARAMETER VALUE

VIN 5 V

VOUT 12 V

IOUT 500 mA POUT 6 W

VD0.4 V PDIODE 236 mW

FSW 1.6 MHz

TRISE 6 nS PSWR 80 mW

TFALL 5 nS PSWF 70 mW

IQ4 mA PQ 20 mW

RDSon 250 mΩPCOND 305 mW

RDCR 75 mΩPIND 145 mW

D0.623

η86% PLOSS 856 mW

PINTERNAL = PCOND + PSW = 475 mW (59)

10.3.5 Calculating RθJA and RΨJC

(60)

Now the internal power dissipation is known, and the junction temperature is attempted to be kept at or below

125°C. The next step is to calculate the value for RθJA and/or RψJC. 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 160°C, the device

shuts down until the temperature reduces to 150°C. Knowing this, the RθJA or the RψJC 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 RψJC is lower than for RθJA . However, a small

thermocouple will need to be attached onto the top case of the LM2735 to obtain the RψJC 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 125°C to

determine what maximum ambient air temperature keeps the silicon below the 125°C 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.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

500

RTJA

PDISS

100

150

200

250

300

350

400

450

TJA

RPnDissipatio

-A

<JC

RPnDissipatio

-Case-Top

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10.3.5.2 Example From Previous Calculations

PDissipation = 475 mW

TAat Shutdown = 139°C

TCase-Top at Shutdown = 155°C

(61)

RθJA WSON = 55°C/W

RψJC WSON = 21°C/W

WSON & MSOP-PowerPAD typical applications will produce RθJA numbers in the range of 50°C/W to 65°C/W,

and RψJC will vary from 18°C/W to 28°C/W. These values are for PCB’s with two and four layer boards with 0.5-

oz copper, and 4 to 6 thermal vias to bottom side ground plane under the DAP.

For 5-pin SOT-23 package typical applications, RθJA numbers will range from 80°C/W to 110°C/W, and RψJC will

vary from 50°C/W to 65°C/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

75°C: 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 RθJA.

Figure 50. RθJA vs Internal Dissipation for the WSON

and MSOP-PowerPAD Package

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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® Tools

Click here to create a custom design using the LM2735 device with the WEBENCH® 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 ® 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 E2E™ 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.

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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.

PACKAGE OPTION ADDENDUM

www.ti.com 6-Feb-2020

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead/Ball Finish

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

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.

PACKAGE OPTION ADDENDUM

www.ti.com 6-Feb-2020

Addendum-Page 2

(4) 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

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device Package

Type Package

Drawing Pins SPQ Reel

Diameter

(mm)

Reel

Width

W1 (mm)

(mm) B0

(mm) K0

(mm) P1

(mm) W

(mm) Pin1

Quadrant

LM2735XMF/NOPB SOT-23 DBV 5 1000 178.0 8.4 3.2 3.2 1.4 4.0 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

PACKAGE MATERIALS INFORMATION

www.ti.com 6-Sep-2019

Pack Materials-Page 1

*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

PACKAGE MATERIALS INFORMATION

www.ti.com 6-Sep-2019

Pack Materials-Page 2

www.ti.com

PACKAGE OUTLINE

0.22

0.08 TYP

0.25

3.0

2.6

2X 0.95

1.9

1.45

0.90

0.15

0.00 TYP

5X 0.5

0.3

0.6

0.3 TYP

0 TYP

1.9

3.05

2.75

1.75

1.45

(1.1)

SOT-23 - 1.45 mm max heightDBV0005A

SMALL OUTLINE TRANSISTOR

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.

0.2 C A B

INDEX AREA

PIN 1

GAGE PLANE

SEATING PLANE

0.1 C

SCALE 4.000

www.ti.com

EXAMPLE BOARD LAYOUT

0.07 MAX

ARROUND 0.07 MIN

ARROUND

5X (1.1)

5X (0.6)

(2.6)

(1.9)

2X (0.95)

(R0.05) TYP

4214839/E 09/2019

SOT-23 - 1.45 mm max heightDBV0005A

SMALL OUTLINE TRANSISTOR

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.

SYMM

LAND PATTERN EXAMPLE

EXPOSED METAL SHOWN

SCALE:15X

PKG

SOLDER MASK

OPENING

METAL UNDER

SOLDER MASK

DEFINED

EXPOSED METAL

METAL

SOLDER MASK

OPENING

NON SOLDER MASK

DEFINED

(PREFERRED)

SOLDER MASK DETAILS

EXPOSED METAL

www.ti.com

EXAMPLE STENCIL DESIGN

(2.6)

(1.9)

2X(0.95)

5X (1.1)

5X (0.6)

(R0.05) TYP

SOT-23 - 1.45 mm max heightDBV0005A

SMALL OUTLINE TRANSISTOR

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.

SOLDER PASTE EXAMPLE

BASED ON 0.125 mm THICK STENCIL

SCALE:15X

SYMM

PKG

www.ti.com

PACKAGE OUTLINE

6X 0.65

1.95

8X 0.38

0.25

5.05

4.75 TYP

SEATING

PLANE

0.15

0.05

0.25

GAGE PLANE

0 -8

1.1 MAX

0.23

0.13

1.88

1.58

2.0

1.7

B3.1

2.9

NOTE 4

3.1

2.9

NOTE 3

0.7

0.4

PowerPAD VSSOP - 1.1 mm max heightDGN0008A

SMALL OUTLINE PACKAGE

4218836/A 11/2019

0.13 C A B

PIN 1 INDEX AREA

SEE DETAIL A

0.1 C

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.

PowerPAD is a trademark of Texas Instruments.

A 20

DETAIL A

TYPICAL

SCALE 4.000

EXPOSED THERMAL PAD

www.ti.com

EXAMPLE BOARD LAYOUT

0.05 MAX

ALL AROUND 0.05 MIN

ALL AROUND

8X (1.4)

8X (0.45)

6X (0.65)

(4.4)

(R0.05) TYP

(2)

NOTE 9

(3)

NOTE 9

(1.22)

(0.55)

( 0.2) TYP

VIA

(1.88)

(2)

PowerPAD VSSOP - 1.1 mm max heightDGN0008A

SMALL OUTLINE PACKAGE

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.

LAND PATTERN EXAMPLE

EXPOSED METAL SHOWN

SCALE: 15X

SYMM

SOLDER MASK

DEFINED PAD

METAL COVERED

BY SOLDER MASK

SEE DETAILS

15.000

METAL

SOLDER MASK

OPENING METAL UNDER

SOLDER MASK SOLDER MASK

OPENING

EXPOSED METAL

SOLDER MASK DETAILS

NON-SOLDER MASK

DEFINED

(PREFERRED)

SOLDER MASK

DEFINED

www.ti.com

EXAMPLE STENCIL DESIGN

8X (1.4)

8X (0.45)

6X (0.65)

(4.4)

(R0.05) TYP

(1.88)

BASED ON

0.125 THICK

STENCIL

(2)

BASED ON

0.125 THICK

STENCIL

PowerPAD VSSOP - 1.1 mm max heightDGN0008A

SMALL OUTLINE PACKAGE

4218836/A 11/2019

1.59 X 1.690.175 1.72 X 1.830.15 1.88 X 2.00 (SHOWN)0.125 2.10 X 2.240.1

SOLDER STENCIL

OPENING

STENCIL

THICKNESS

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. Board assembly site may have different recommendations for stencil design.

SOLDER PASTE EXAMPLE

EXPOSED PAD 9:

100% PRINTED SOLDER COVERAGE BY AREA

SCALE: 15X

SYMM

METAL COVERED

BY SOLDER MASK SEE TABLE FOR

DIFFERENT OPENINGS

FOR OTHER STENCIL

THICKNESSES

MECHANICAL DATA

NGG0006A

www.ti.com

SDE06A (Rev A)

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