AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications General Description Features The AAT1231/1231-1 are high frequency, high efficiency constant current boost converters capable of 24V maximum output voltage. Both devices are ideal power solutions for backlight applications with up to six white LEDs in series or up to twelve white LEDs in a parallel/series configuration. The input voltage is 2.7V to 5.5V for single-cell lithiumion/polymer (Li-ion) based portable devices. * * * The LED current is digitally controlled across a 6x operating range using AnalogicTech's Simple Serial ControlTM (S2CwireTM) interface. Programmability across 26 discrete current steps provides high resolution, low noise, flicker-free, constant LED outputs. In programming AAT1231 operation, LED brightness increases based on the data received at the EN/SET pin. In programming AAT1231-1 operation, LED brightness decreases based on the data received at the EN/SET pin. The SEL logic pin changes the feedback voltage between two programmable ranges. The AAT1231 and the AAT1231-1 feature high current limit and fast, stable transitions for stepped or pulsed current applications. The high switching frequency (up to 2MHz) provides fast response and allows the use of ultra-small external components, including chip inductors and capacitors. Fully integrated control circuitry simplifies design and reduces total solution size. The AAT1231 and the AAT1231-1 offer a true load disconnect feature which isolates the load from the power source while in the OFF or disabled state. This eliminates leakage current, making the devices ideally suited for battery-powered applications. The AAT1231 and the AAT1231-1 are available in Pbfree, thermally-enhanced 12-pin TSOPJW packages. * * * * * * * * * * SwitchRegTM Input Voltage Range: 2.7V to 5.5V Maximum Continuous Output 24V @ 50mA Drives 6 LEDs in Series, 12 LEDs in Parallel/ Series Configuration -- Constant LED Current with 6% Accuracy Digital Control with S2Cwire Single Wire Interface -- 26 Discrete Steps -- No PWM Control Required -- No Additional Circuitry Up to 82% Efficiency Up to 2MHz Switching Frequency Allows Small External Chip Inductor and Capacitors Hysteretic Control -- No External Compensation Components -- Excellent Load Transient Response -- High Efficiency at Light Loads Integrated Soft Start with No External Capacitor True Load Disconnect Guarantees <1.0A Shutdown Current Selectable Feedback Voltage Ranges for High Resolution Control of Load Current Short-Circuit, Over-Voltage, and OverTemperature Protection 12-Pin TSOPJW Package -40C to +85C Temperature Range Applications * * * * * Digital Still Cameras (DSCs) Mobile Handsets MP3 Players PDAs and Notebook PCs White LED Drivers Typical Application L = 2.2H C1 2.2F LIN VIN SW PGND Li-Ion: VIN = 2.7V to 4.2V Select R3 12k Capable of Driving Six LEDs in Series (see Applications Section) FB AGND OSRAM LW M678 C2 2.2F EN/SET SEL Up to 24V/ 50mA max R2 226k OVP AAT1231/ 1231-1 Enable/Set 1231.2006.08.1.1 PVIN DS1 R1 (RBALLAST) 30.1 1 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications Pin Descriptions Pin # Symbol 1 PVIN 2 3 EN/SET SEL 4 5 6, 7 8 9 10 11 12 VIN N/C SW PGND AGND FB OVP LIN Function Input power pin; connected to the source of the P-channel MOSFET. Connect to the input capacitor(s). IC enable pin and S2Cwire input control to set output current. FB voltage range select. For the AAT1231, a logic LOW sets the FB voltage range from 0.1V to 0.4V; a logic HIGH sets the FB voltage range from 0.3V to 0.6V. For the AAT1231-1, a logic LOW sets the FB voltage range from 0.4V to 0.1V; a logic HIGH sets the FB voltage range from 0.6V to 0.3V. Input voltage for the converter. Connect directly to the PVIN pin. No connection. Boost converter switching node. Connect the power inductor between this pin and LIN. Power ground for the boost converter. Ground pin. Feedback pin. Connect a resistor to ground to set the maximum LED current. Feedback pin for over-voltage protection sense. Switched power input. Connect the power inductor between this pin and SW. Pin Configuration TSOPJW-12 (Top View) PVIN EN/SET SEL VIN N/C SW 2 1 12 2 11 3 10 4 9 5 8 6 7 LIN OVP FB AGND PGND SW 1231.2006.08.1.1 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications Part Number Descriptions SEL Polarity Part Number HIGH LOW S2C Feedback Voltage Programming AAT1231ITP AAT1231ITP-1 0.3V VFB 0.6V 0.6V VFB 0.3V 0.1V VFB 0.4V 0.4V VFB 0.1V See Table 2 See Table 3 Absolute Maximum Ratings1 TA = 25C unless otherwise noted. Symbol PVIN, VIN SW LIN, EN/SET, SEL, FB TJ TS TLEAD Description Value Units Input Voltage Switching Node -0.3 to 6.0 28 V V Maximum Rating VIN + 0.3 V -40 to 150 -65 to 150 300 C C C Value Units 160 625 C/W mW Operating Temperature Range Storage Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Thermal Information Symbol JA PD Description Thermal Resistance Maximum Power Dissipation 1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time. 1231.2006.08.1.1 3 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications Electrical Characteristics1 TA = -40C to +85C unless otherwise noted. Typical values are at 25C, VIN = 3.6V. Symbol Power Supply PVIN, VIN VOUT(MAX) IQ ISHDN IOUT VLINEREG(FB)/ VIN RDS(ON) L RDS(ON) IN TSS VOVP ILIMIT TSD THYS SEL, EN/SET VSEL(L) VSEL(H) VEN/SET(L) VEN/SET(H) TEN/SET (LO) TEN/SET(HI) TOFF TLAT IEN/SET AAT1231 FB Description Conditions Input Voltage Range Maximum Output Voltage Operating Current Shutdown Current Maximum Continuous Output Current2 SEL = GND, FB = 0.1V EN/SET = GND Line Regulation VIN = 2.7V to 5.5V, VFB = 0.6V Min 2.7 40 2.7V < VIN < 5.5V, VOUT = 24V Low Side Switch On Resistance Input Disconnect Switch On Resistance From Enable to Output Regulation; VFB = 300mV Over-Voltage Protection Threshold VOUT Rising Over-Voltage Hysteresis VOUT Falling N-Channel Current Limit TJ Thermal Shutdown Threshold TJ Thermal Shutdown Hysteresis Soft-Start Time SEL Threshold Low SEL Threshold High Enable Threshold Low Enable Threshold High EN/SET Low Time EN/SET High Time EN/SET Off Timeout EN/SET Latch Timeout EN/SET Input Leakage FB Pin Regulation Typ 1.1 Max Units 5.5 24 70 1.0 V V A A 50 mA 0.7 %/V 80 m 180 m 300 s 1.2 100 2.5 140 15 1.3 V mV A C C 0.4 V V V V s ns s s A 1.4 0.4 VEN/SET VEN/SET VEN/SET VEN/SET VEN/SET < > < > = 0.6V 1.4V 0.6V 1.4V 5V VIN = 5V VIN = 2.7V to 5.5V, SEL = GND, EN/SET = HIGH VIN = 2.7V to 5.5V, SEL = HIGH, EN/SET = DATA16 1.4 0.3 50 -1 75 75 500 500 1 0.09 0.1 0.11 0.564 0.6 0.636 0.09 0.1 0.11 V AAT1231-1 FB FB Pin Regulation VIN = 2.7V to 5.5V, SEL = GND, EN/SET = DATA16 VIN = 2.7V to 5.5V, SEL = HIGH, EN/SET = HIGH V 0.564 0.6 0.636 1. Specification over the -40C to +85C operating temperature range is assured by design, characterization, and correlation with statistical process controls. 2. Maximum continuous output current increases with reduced output voltage, but may vary depending on operating efficiency and thermal limitations. 4 1231.2006.08.1.1 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications Typical Characteristics Efficiency vs. LED Current Efficiency vs. LED Current (4 White LEDs; RBALLAST = 30.1 ) (5 White LEDs; RBALLAST = 30.1 ) 85 83 VIN = 5V 82 83 Efficiency (%) Efficiency (%) 84 82 81 80 VIN = 4.2V VIN = 3.6V 79 78 VIN = 5V 81 80 VIN = 4.2V 79 VIN = 3.6V 78 77 76 77 75 2 4 6 8 10 12 14 16 18 20 2 4 6 LED Current (mA) 12 14 16 18 20 18 20 Efficiency vs. LED Current (6 White LEDs; RBALLAST = 30.1 ) (12 White LEDs; RBALLAST = 30.1 ) 84 81 80 83 VIN = 5V 79 78 VIN = 4.2V 77 76 VIN = 3.6V 75 VIN = 5V 82 Efficiency (%) Efficiency (%) 10 LED Current (mA) Efficiency vs. LED Current 81 80 79 VIN = 4.2V 78 77 VIN = 3.6V 76 74 75 73 74 2 4 6 8 10 12 14 16 18 20 2 4 6 LED Current (mA) 10 12 14 16 Feedback Voltage vs. Temperature (RBALLAST = 30.1 ) (EN = GND) 700 Feedback Voltage (mV) 1.0 0.8 0.6 85C 0.4 25C 0.2 0.0 2.7 8 LED Current (mA) Shutdown Current vs. Input Voltage Shutdown Current (A) 8 -40C 600 500 400 300 200 100 0 3.1 3.5 3.9 4.3 Input Voltage (V) 1231.2006.08.1.1 4.7 5.1 5.5 -40 -15 10 35 60 85 Temperature (C) 5 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications Typical Characteristics Accuracy ILED vs. Temperature Accuracy ILED vs. Input Voltage (VFB = 0.6V; RBALLAST = 30.1 ) 1.0 2.0 0.8 1.5 Accuracy ILED (%) Accuracy ILED (%) (VFB = 0.6V; RBALLAST = 30.1 ) 0.5 0.3 0.0 -0.3 -0.5 1.0 -40C 0.5 0.0 -0.5 25C -1.0 -1.5 -0.8 -2.0 -1.0 -40 -15 10 35 60 85 2.7 3.2 20.2 5.2 5.7 0.8 0.6 0.4 2.5V 0V 0.6 0.4 0.2 0 0.5 0.0 Time (50s/div) Inductor Current (A) (bottom) 20.4 Enable Voltage (V) (top) Feedback Voltage (V) (middle) Shutdown (VFB = 0.6V; ILED = 20mA) 20.6 Time (50s/div) Output Ripple Output Ripple (6 White LEDs; ILED = 13mA) (6 White LEDs; ILED = 20mA) VOUT (DC Offset 20.7V) (20mV/div) VOUT (DC Offset 19.8V) (50mV/div) 20 VLX (V) 0 20 0 0.5 0.5 IL (A) 4.7 Line Transient 3.6V VLX (V) 4.2 (6 White LEDs; RBALLAST = 30.1) 4.2V 20.8 3.7 Input Voltage (V) Feedback Voltage (bottom) (V) Input Voltage (top) (V) Output Voltage (middle) (V) Temperature (C) IL (A) 0 Time (400ns/div) 6 85C 0 Time (200ns/div) 1231.2006.08.1.1 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications AAT1231 Soft Start (6 White LEDs; VFB = 0.6V) (6 White LEDs; VFB = 0.3V) 0V 0.4 0.2 0 2 1 0 2.5V 0V 0.2 0 2 1 0 Time (100s/div) Time (50s/div) AAT1231-1 Soft Start with S2Cwire AAT1231-1 Soft Start (6 White LEDs; VFB = 0.6V) 0V 0.4 0.2 0 1 0 Enable Voltage (top) (V) Feedback Voltage (middle) (V) 2.5V 2.5V 0.6 0V 0.4 0.2 0 1 0 Time (50s/div) Time (100s/div) Transition of LED Current (6 White LEDs; SEL = Low; ILED = 3.3mA to 13.3mA) 20 18 0.4 0.3 0.2 0.1 0.0 Time (20s/div) 1231.2006.08.1.1 22 20 18 0.4 0.3 0.2 0.1 0.0 Feedback Voltage (bottom) (V) 22 Output Voltage (top) (V) Transition of LED Current (6 White LEDs; SEL = Low; ILED = 13.3mA to 6.6mA) Feedback Voltage (bottom) (V) Output Voltage (top) (V) Inductor Current (bottom) (A) Inductor Current (bottom) (A) Enable Voltage (top) (V) Feedback Voltage (middle) (V) (6 White LEDs; VFB = 0.3V) 0.6 Inductor Current (bottom) (A) 2.5V Enable Voltage (top) (V) Feedback Voltage (middle) (V) AAT1231 Soft Start with S2Cwire Inductor Current (bottom) (A) Enable Voltage (top) (V) Feedback Voltage (middle) (V) Typical Characteristics Time (20s/div) 7 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications Typical Characteristics EN/SET Off Timeout vs. Input Voltage 300 350 300 EN/SET Off Timeout (s) EN/SET Latch Timeout (s) EN/SET Latch Timeout vs. Input Voltage 25C -40C 250 85C 200 150 100 -40C 250 200 85C 150 100 50 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 2.7 3.1 3.5 Input Voltage (V) 4.7 5.1 5.5 1.2 1.1 1.1 -40C 1.0 0.9 0.8 0.7 85C 25C 0.6 -40C 1.0 VIH (V) VIL (V) 4.3 EN/SET High Threshold vs. Input Voltage 1.2 0.9 25C 0.8 85C 0.7 0.6 0.5 0.5 0.4 2.7 3.1 3.5 3.9 4.3 4.7 5.1 0.4 2.7 5.5 3.1 3.5 Input Voltage (V) 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Low Side Switch On Resistance vs. Input Voltage Input Disconnect Switch Resistance vs. Input Voltage 160 300 280 120C 120 RDS(ON)IN (m ) 140 RDS(ON)L (m) 3.9 Input Voltage (V) EN/SET Low Threshold vs. Input Voltage 100C 100 80 25C 60 85C 2.5 3 3.5 120C 260 4 4.5 Input Voltage (V) 5 5.5 6 100C 240 220 200 180 25C 160 40 8 25C 140 2.5 3 85C 3.5 4 4.5 5 5.5 6 Input Voltage (V) 1231.2006.08.1.1 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications Functional Block Diagram LIN PVIN VIN OVP EN/SET FB SW Reference Output Select Control SEL AGND PGND Functional Description age overshoot across the full input voltage range and all loading conditions. The AAT1231 and the AAT1231-1 consist of a DC/DC boost controller, an integrated slew rate controlled input disconnect MOSFET switch, and a high voltage MOSFET power switch. A high voltage rectifier, power inductor, output capacitor, and sense resistors are required to implement a DC/DC constant current boost converter. The input disconnect switch is activated when a valid input voltage is present and the EN/SET pin is pulled high. The slew rate control on the P-channel MOSFET ensures minimal inrush current as the output voltage is charged to the input voltage, prior to the switching of the N-channel power MOSFET. Monotonic turn-on is guaranteed by the integrated soft-start circuitry. Soft-start eliminates output volt- The maximum current through the LED string is set by the ballast resistor and the feedback voltage of the IC. The output current may be programmed by adjusting the level of the feedback reference voltage which is programmed through the S2Cwire interface. The SEL pin selects one of two feedback voltage ranges. For the AAT1231 and with a LOW logic level applied to the SEL pin, the FB pin voltage can be programmed from 0.1V to 0.4V. With a logic HIGH applied to the SEL pin, the FB pin voltage can be programmed from 0.3V to 0.6V. In the AAT1231-1, the SEL function is inverted in that the FB pin voltage can be programmed from 0.4V to 0.1V with a logic LOW applied to the SEL pin and 0.6V to 0.3V with a logic HIGH applied to the SEL 1231.2006.08.1.1 9 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications pin. Regardless of which device is chosen, the feedback voltage can be set to any one of 16 current levels within each FB range, providing highresolution control of the LED current, using the single-wire S2Cwire control. grammed current source connected to the output capacitor, parallel with the LED string and ballast resistor. There is no right-half plane zero, and loop stability is achieved with no additional compensation components. For torch and flash applications where a short duration, pulsed load is desired, applying a lowto-high transition on the AAT1231's SEL pin produces a 1.5x to 3.0x LED current step. In the AAT1231-1 on the other hand, the LED current step for a low-to-high transition on the SEL pin can be programmed from 3.0x to 1.5x. In both products, the step size is determined by the programmed voltage at the FB pin where the internal default setting is 3.0x in the AAT1231 and 1.5x in the AAT1231-1. An increase in the feedback voltage (VFB) results in an increased error signal sensed across the ballast resistor (R1). The controller responds by increasing the peak inductor current, resulting in higher average current in the inductor and LED string(s). Alternatively, when the VFB is reduced, the controller responds by decreasing the peak inductor current, resulting in lower average current in the inductor and LED string(s). Control Loop The AAT1231/1231-1 provide the benefits of current mode control with a simple hysteretic output current loop providing exceptional stability and fast response with minimal design effort. The device maintains exceptional constant current regulation, transient response, and cycle-by-cycle current limit without additional compensation components. The AAT1231/1231-1 modulate the power MOSFET switching current to maintain the programmed FB voltage. This allows the FB voltage loop to directly program the required inductor current in order to maintain the desired LED current. The switching cycle initiates when the N-channel MOSFET is turned ON and current ramps up in the inductor. The ON interval is terminated when the inductor current reaches the programmed peak current level. During the OFF interval, the input current decays until the lower threshold, or zero inductor current, is reached. The lower current is equal to the peak current minus a preset hysteresis threshold, which determines the inductor ripple current. The peak current is adjusted by the controller until the LED output current requirement is met. The magnitude of the feedback error signal determines the average input current. Therefore, the AAT1231/1231-1 controller implements a pro- 10 Under light load conditions, the inductor OFF interval current goes below zero and the boost converter enters discontinuous mode operation. Further reduction in the load current results in a corresponding reduction in the switching frequency. The AAT1231/1231-1 provide pulsed frequency operation which reduces switching losses and maintains high efficiency under light load conditions. Operating frequency varies with changes in the input voltage, output voltage, and inductor size. Once the boost converter has reached continuous mode, further increases in the LED current will not significantly change the operating frequency. A small 2.2H (20%) inductor is selected to maintain high frequency switching (up to 2MHz) and high efficiency operation for outputs up to 24V. Soft Start / Enable The input disconnect switch is activated when a valid input voltage is present and the EN/SET pin is pulled high. The slew rate control on the Pchannel MOSFET ensures minimal inrush current as the output voltage is charged to the input voltage, prior to switching of the N-channel power MOSFET. Monotonic turn-on is guaranteed by the built-in soft-start circuitry. Soft start eliminates output current overshoot across the full input voltage range and all loading conditions. After the soft start sequence has terminated, the initial LED current is determined by the internal, default FB voltage across the external ballast resistor at the FB pin. Additionally, the AAT1231 and the 1231.2006.08.1.1 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications AAT1231-1 have been designed to offer the system designer two choices for the default FB voltage based on the state of the SEL pin. Changing the LED current from its initial default setting is easy by using the S2Cwire single wire serial interface; the FB voltage can be increased (as in the AAT1231; see Table 2) or decreased (as in the AAT1231-1; see Table 3) relative to the default FB voltage. Current Limit and Over-Temperature Protection The switching of the N-channel MOSFET terminates when a current limit of 2.5A (typical) is exceeded. This minimizes power dissipation and component stresses under overload and short-circuit conditions. Switching resumes when the current decays below the current limit. Application Information Over-Voltage Protection OVP Protection with Open Circuit Failure The OVP protection circuit consists of a resistor network tied from the output voltage to the OVP pin (see Figure 1). To protect the device from open circuit failure, the resistor divider can be selected such that the over-voltage threshold occurs prior to the output reaching 24V (VOUT(MAX)). The value of R3 should be selected from 10k to 20k to minimize losses without degrading noise immunity. R2 = R 3 * Thermal protection disables the AAT1231/1231-1 when internal dissipation becomes excessive. Thermal protection disables both MOSFETs. The junction over-temperature threshold is 140C with 15C of temperature hysteresis. The output voltage automatically recovers when the over-temperature fault condition is removed. VOUT(MAX) -1 VOVP VOUT AAT1231/1231-1 R2 COUT OVP R3 GND Over-Voltage Protection Internal bias of all circuits is controlled via the VIN input. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry prior to soft start. 1231.2006.08.1.1 Over Voltage Protection Pin (top) (V) Inductor Current (bottom (A) Under-Voltage Lockout Figure 1: Over-Voltage Protection Circuit. 1.224V 1.168V 26 24 22 2 1 0 Output Voltage (middle) (V) Over-voltage protection prevents damage to the AAT1231/1231-1 during open-circuit or high output voltage conditions. An over-voltage event is defined as a condition where the voltage on the OVP pin exceeds the Over-Voltage Threshold Limit (VOVP = 1.2V typical). When the voltage on the OVP pin has reached the threshold limit, the converter stops switching and the output voltage decays. Switching resumes when the voltage on the OVP pin drops below the lower hysteresis limit, maintaining an average output voltage between the upper and lower OVP thresholds multiplied by the resistor divider scaling factor. Time (5ms/div) Figure 2: Over-Voltage Protection Open Circuit Response (No LED). 11 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications Assume R3 = 12k and VOUT(MAX) = 24V. Selecting 1% resistor for high accuracy, this results in R2 = 226k (rounded to the nearest standard value). The minimum OVP threshold can be calculated: VOUT(OVP_MIN) = VOVP(MIN) * R2 +1 R3 = 21.8V To avoid OVP detection and subsequent reduction in the programmed output current (see following section), the maximum operating voltage should not exceed the minimum OVP set point. VOUT(MAX) < VOUT(OVP_MIN) ensure DC current and negligible flicker in the LED string(s). The waveform in Figure 3 shows the output voltage and LED current at cold temperature with a six series white LED string and VOVP = 19.4V. As shown, the output voltage rises as a result of the increased VFLED which triggers the OVP constant voltage operation. Self heating of the LEDs triggers a smooth transition back to constant current control. OVP Constant Voltage Operation Cold Temperature Applied ILED (10mA/div) In some cases, this may disallow configurations with high LED forward voltage (VFLED) and/or greater than five series white LEDs. VFLED unit-tounit tolerance can be as high as +15% of nominal for white LED devices. OVP Constant Voltage Operation Under closed loop constant current conditions, the output voltage is determined by the operating current, LED forward voltage characteristics (VFLED), quantity of series connected LEDs (N), and the feedback pin voltage (VFB). VOUT = VFB + N * VFLED When the rising OVP threshold is exceeded, switching is stopped and the output voltage decays. Switching automatically restarts when the output drops below the lower OVP hysteresis voltage (100mV typical) and, as a result, the output voltage increases. The cycle repeats, maintaining an average DC output voltage proportional to the average of the rising and falling OVP levels (multiplied by the resistor divider scaling factor). High operating frequency and small output voltage ripple 12 Self-Recovery VOUT (5V/div) ILED Time (1s/div) Figure 3: Over-Voltage Protection Constant Voltage Operation (6 White LEDs; ILED = 13mA; ; R3 = 12k ). R2 = 182k While OVP is active, the maximum LED current programming error (ILED) is proportional to voltage error across an individual LED (VFLED). VFLED = (N * VFLED(MAX) - VOUT(OVP_MIN) - VFB) N To minimize the ILED error, the minimum OVP voltage (VOUT(OVP_MIN)) may be increased, yielding a corresponding increase in the maximum OVP voltage (VOUT(OVP_MAX)). Measurements should confirm that the maximum switching node voltage (VSW(MAX)) is less than 28V under worst-case operating conditions. 1231.2006.08.1.1 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications VSW(MAX) = VOVP(MAX) * R3 + 1 + VF + VRING R2 VF = Schottky Diode DS1 forward voltage at turnOFF VRING = Voltage ring occurring at turn-OFF LED Selection and Current Setting The AAT1231/1231-1 are well suited for driving white LEDs with constant current. Applications include main and sub-LCD display backlighting, and color LEDs. The LED current is controlled by the FB voltage and the ballast resistor. For maximum accuracy, a 1% tolerance resistor is recommended. The ballast resistor (RBALLAST) value can be calculated as follows: RBALLAST = VFB(MAX) ILED(MAX) Typical white LEDs are driven at maximum continuous currents of 15mA to 20mA. For maximum output, two parallel strings of six series LEDs are used. A total output current of 30mA or 40mA is required (15mA to 20mA in each string). The maximum quantity of series connected LEDs is determined by the minimum OVP voltage of the boost converter (VOUT(OVP_MIN)), minus the maximum feedback voltage (VFB(MAX)) divided by the maximum LED forward voltage (V FLED(MAX)). VFLED(MAX) can be estimated from the manufacturers' datasheet at the maximum LED operating current. VOUT(OVP_MIN) = VOVP(MIN) * N= (VOUT(OVP_MIN) - VFB(MAX)) VFLED(MAX) Figure 4 shows the schematic of using six LEDs in series. Assume VFLED @ 20mA = 3.5V (typical) from LW M673 (OSRAM) datasheet. where: VFB(MAX) = 0.4V when SEL = Low VFB(MAX) = 0.6V when SEL = High VOUT(OVP_MIN) = 1.1V * i.e., for a maximum LED current of 20mA (SEL = High): N= RBALLAST = R2 +1 R3 VFB 0.6 = = 30 30.1 ILED(MAX) 0.020 ) RBALLAST ( Maximum ILED Current (mA) SEL = High SEL = Low 50 40 35 30 25 20 15 10 5 12.1 15.0 16.9 20.0 24.3 30.1 40.2 60.4 121.0 8.06 10.0 11.3 13.3 16.2 20.0 26.7 40.2 80.6 226k + 1 = 21.82V 12k 21.82V - 0.6V 3.5V 6.1 Therefore, under typical operating conditions, six LEDs can be used in series. Table 1: Maximum LED Current and RBALLAST Resistor Values (1% Resistor Tolerance). 1231.2006.08.1.1 13 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications VIN = 2.7V to 5.5V JP1 1 R4 10K 2 C1 2.2F DS1 L1 3 Enable JP2 2.2H U1 AAT1231/1231-1 1 2 3 4 5 6 VIN EN SEL VP N/C SW LIN OVP FB GND PGND SW VOUT = 24V/20mA R2 226K 12 11 10 R3 12K 9 8 7 TSOP12JW 1 2 3 Select R1 D6 D5 30.1 LED LED D1 LED D2 LED D3 LED C2 2.2F D4 LED U1 AAT1231/1231-1 TSOPJW-12 L1 2.2H SD3814-2R2 C1 2.2F 10V 0603 C2 2.2F 25V 0805 D1-D6 LW M673 White LED DS1 30V 0.2A BAT42W SOD-123 R1 30.1 0603 R2 226K 0603 R3 12K 0603 R4 10K 0603 Figure 4: AAT1231/1231-1 White LED Boost Converter Schematic. LED Brightness Control 14 LED Current (mA) The AAT1231 and the AAT1231-1 use S2Cwire programming to control LED brightness and does not require PWM (pulse width modulation) or additional control circuitry. This feature greatly reduces the burden on a microcontroller or system IC to manage LED or display brightness, allowing the user to "set it and forget it." With its high-speed serial interface (1MHz data rate), the output current of the AAT1231 and the AAT1231-1 can be changed successively to brighten or dim the LEDs in smooth transitions (i.e., to fade out) or in abrupt steps, giving the user complete programmability and realtime control of LED brightness. 25 20 SEL = HIGH 15 10 (Default) SEL = LOW 5 0 1 4 7 10 13 16 S2Cwire Data Register Figure 5: Programming AAT1231 LED Current . with RBALLAST = 30.1 1231.2006.08.1.1 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications 3. 5 Select Pin Scaling Factor (Low to High) 25 LED Current (mA) 20 SEL=HIGH (Default) 15 10 SEL=LOW 5 0 1 4 7 10 13 16 (Default) 1. 5 1. 0 4 7 10 13 16 Figure 8: AAT1231-1 SEL Pin Scaling Factor: ILED (SEL = High) Divided by ILED (SEL = Low). Alternatively, toggling the SEL logic pin from low to high implements stepped or pulsed LED currents by increasing the FB pin voltage. Figures 7 and 8 illustrate the SELECT pin scaling factor, defined as the LED current with SEL=HIGH divided by the LED current with SEL=LOW. For the AAT1231, scaling factors from 1.5x to 3.0x are possible, depending on the S2Cwire data register (default = 3.0x). In the AAT1231-1, the possible scaling factors are 3.0x to 1.5x with the internal default setting of 1.5x. S2Cwire Serial Interface AnalogicTech's S2Cwire single wire serial interface is a proprietary high-speed single-wire interface available only from AnalogicTech. The S2Cwire interface records rising edges of the EN/SET input and decodes them into 16 individual states. Each state corresponds to a reference feedback voltage setting on the FB pin, as shown in Table 2. S2Cwire Serial Interface Timing 3.5 Select Pin Scaling Factor (High to Low) 2. 0 S2Cwire Data Register Figure 6: Programming AAT1231-1 LED . Current with RBALLAST = 30.1 (Default) 3.0 2.5 2.0 1.5 1.0 4 7 10 13 16 S2Cwire Data Register Figure 7: AAT1231 SEL Pin Scaling Factor: ILED (SEL = High) Divided by ILED (SEL = Low). 1231.2006.08.1.1 2. 5 1 S2Cwire Data Register 1 3. 0 The S2Cwire single wire serial interface data can be clocked-in at speeds up to 1MHz. After data has been submitted, EN/SET is held high to latch the data for a period TLAT. The FB pin voltage is subsequently changed to the level as defined by the state of the SEL logic pin. When EN/SET is set low for a time greater than TOFF, the AAT1231/1231-1 is disabled. When either the AAT1231 or the AAT1231-1 is disabled, the register is reset to its default value. In the AAT1231, the default register value sets the FB pin voltage to 0.6V if the EN/SET pin is subsequently pulled HIGH. In the AAT1231-1, the FB pin voltage is set to 0.3V under the same condition. 15 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications S2Cwire Feedback Voltage Programming edges applied at the EN/SET pin determine the FB pin voltage. If a logic LOW is applied at the SEL pin, the default feedback voltage range for the AAT1231 is 0.1V to 0.4V; for a logic HIGH condition at the SEL pin, the default feedback voltage range is 0.3V to 0.6V. Conversely, if a logic LOW is applied at the SEL pin of the AAT1231-1, the default feedback voltage range becomes 0.4V to 0.1V and 0.6V to 0.3V for a logic HIGH condition at the SEL pin. The FB pin voltage is set to the default level at initial powerup. The AAT1231 and the AAT1231-1 are programmed through the S2Cwire interface. Table 2 illustrates FB pin voltage programming for the AAT1231 and Table 3 illustrates FB pin voltage programming for the AAT1231-1. The rising clock THI TLO TOFF T LAT EN/SET 1 Data Reg 2 n-1 n 16 0 n-1 0 Figure 9: AAT1231/1231-1 S2Cwire Timing Diagram to Program the Output Voltage. Rising Clock Edges/Data Register 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 SEL = Low Reference LED Current (mA); Voltage (V) RBALLAST = 30.1 SEL = High Reference LED Current (mA); Voltage (V) RBALLAST = 30.1 0.1 (default) 0.12 0.14 0.16 0.18 0.20 0.22 0.24 0.26 0.28 0.30 0.32 0.34 0.36 0.38 0.40 0.3 (default) 0.32 0.34 0.36 0.38 0.40 0.42 0.44 0.46 0.48 0.50 0.52 0.54 0.56 0.58 0.60 3.32 3.99 4.65 5.32 5.98 6.64 7.31 7.97 8.64 9.30 9.97 10.63 11.30 11.96 12.62 13.29 9.97 10.63 11.30 11.96 12.62 13.29 13.95 14.62 15.28 15.95 16.61 17.28 17.94 18.60 19.27 19.93 Table 2: AAT1231 S2Cwire Reference Feedback Voltage Control Settings with RBALLAST = 30.1 (Assume Nominal Values). 16 1231.2006.08.1.1 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications Rising Clock Edges/Data Register 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 SEL = Low Reference LED Current (mA); Voltage (V) RBALLAST = 30.1 Reference Voltage (V) 0.4 (default) 0.38 0.36 0.34 0.32 0.30 0.28 0.26 0.24 0.22 0.20 0.18 0.16 0.14 0.12 0.10 0.6 (default) 0.58 0.56 0.54 0.52 0.50 0.48 0.46 0.44 0.42 0.40 0.38 0.36 0.34 0.32 0.30 13.29 12.62 11.96 11.30 10.63 9.97 9.30 8.64 7.97 7.31 6.64 5.98 5.32 4.65 3.99 3.32 SEL = High LED Current (mA); RBALLAST = 30.1 19.93 19.27 18.60 17.94 17.28 16.61 15.95 15.28 14.62 13.95 13.29 12.62 11.96 11.30 10.63 9.97 Table 3: AAT1231-1 S2Cwire Reference Feedback Voltage Control Settings With RBALLAST = 30.1 (Assumes Nominal Values). Selecting the Schottky Diode To ensure minimum forward voltage drop and no recovery, high voltage Schottky diodes are considered the best choice for the AAT1231/1231-1 boost converters. The output diode is sized to maintain acceptable efficiency and reasonable operating junction temperature under full load operating conditions. Forward voltage (VF) and package thermal resistance (JA) are the dominant factors to consider in selecting a diode. The diode non-repetitive peak forward surge current rating (IFSM) should be considered for high pulsed load applications, such as camera flash. IFSM rating drops with increasing conduction period. Manufacturers' datasheets should be consulted to verify reliability under peak loading conditions. The diode's published current rating may not reflect actual operating conditions 1231.2006.08.1.1 and should be used only as a comparative measure between similarly rated devices. 20V rated Schottky diodes are recommended for outputs less than 15V, while 30V rated Schottky diodes are recommended for outputs greater than 15V. The switching period is divided between ON and OFF time intervals. 1 = TON + TOFF FS During the ON time, the N-channel power MOSFET is conducting and storing energy in the boost inductor. During the OFF time, the N-channel power MOSFET is not conducting. Stored energy is transferred from the input battery and boost inductor to the output load through the output diode. 17 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications Duty cycle is defined as the ON time divided by the total switching interval. Forward Current (mA) D= 10000 TON TON + TOFF = TON FS B340LA MBR0530T 1000 ZHCS350 100 BAT42W 10 0.00 The maximum duty cycle can be estimated from the relationship for a continuous mode boost converter. Maximum duty cycle (DMAX) is the duty cycle at minimum input voltage (VIN(MIN)). DMAX = 0.10 0.30 0.40 0.50 0.60 0.70 Forward Voltage (V) The average diode current is equal to the output current. IAVG(TOT) = IOUT VOUT - VIN(MIN) VOUT The average diode current during the OFF time can be estimated. IAVG(OFF) = 0.20 The average output current multiplied by the forward diode voltage determines the loss of the output diode. IOUT 1 - DMAX PLOSS(DIODE) = IAVG(TOT) * VF = IOUT * VF The following curves show the VF characteristics for different Schottky diodes (100C case). The VF of the Schottky diode can be estimated from the average current during the off time. For continuous LED currents, the diode junction temperature can be estimated. TJ(DIODE) = TAMB + JA * PLOSS(DIODE) Manufacturer Diodes, Inc. Diodes, Inc. ON Semi Zetex Central Semi Part Number Rated Forward Current (A) Non-Repetitive Peak Surge Current (A) Rated Voltage (V) Thermal Resistance JA, C/W) ( Case B340LA BAT42W MBR0530T ZHCS350 CMDSH2-3 3 0.2 0.5 0.35 0.2 70.0 4.0 5.5 4.2 1.0 40 30 30 40 30 25 500 206 330 500 SMA SOD-123 SOD-123 SOD-523 SOD-323 Table 4: Typical Surface Mount Schottky Rectifiers for Various Output Levels. 18 1231.2006.08.1.1 AAT1231/1231-1 Output diode junction temperature should be maintained below 110C, but may vary depending on application and/or system guidelines. The diode JA can be minimized with additional PCB area on the cathode. PCB heat-sinking the anode may degrade EMI performance. The reverse leakage current of the rectifier must be considered to maintain low quiescent (input) current and high efficiency under light load. The rectifier reverse current increases dramatically at elevated temperatures. Switching Frequency (MHz) Step-Up DC/DC Converters for White LED Backlight Applications 2.0 VIN = 3.0V VOUT = 18V 1.8 VIN = 3.0V VOUT = 15V 1.6 VIN = 3.6V VOUT = 18V 1.4 VIN = 3.6V VOUT = 15V 1.2 1.0 0.8 0.6 VIN = 2.7V VOUT = 18V 0.4 40 VIN = 2.7V VOUT = 15V 50 60 70 80 90 100 Selecting the Boost Inductor The AAT1231 and the AAT1231-1 controllers utilize hysteretic control and the switching frequency varies with output load and input voltage. The value of the inductor determines the maximum switching frequency of the boost converter. Increased output inductance decreases the switching frequency, resulting in higher peak currents and increased output voltage ripple. To maintain 2MHz maximum switching frequency and stable operation, an output inductor sized from 1.5H to 2.7H is recommended. A better estimate of DMAX is possible once VF is known. DMAX = (VOUT + VF - VIN(MIN)) (VOUT + VF) Where VF is the Schottky diode forward voltage. If not known, it can be estimated at 0.5V. Manufacturer's specifications list both the inductor DC current rating, which is a thermal limitation, and peak inductor current rating, which is determined by the saturation characteristics. Measurements at full load and high ambient temperature should be completed to ensure that the inductor does not saturate or exhibit excessive temperature rise. The output inductor (L) is selected to avoid saturation at minimum input voltage, maximum output load conditions. Peak current may be estimated using the following equation, assuming continuous conduction mode. Worst-case peak current occurs at minimum input voltage (maximum duty cycle) and maximum load. Switching frequency (FS) can be estimated from the curves and assumes a 2.2H inductor. 1231.2006.08.1.1 Switching Frequency (MHz) Output Current (mA) 2.0 1.8 VIN = 3.0V VOUT = 12V 1.6 VIN = 3.0V VOUT = 10V VIN = 3.6V VOUT = 12V VIN = 3.6V VOUT = 10V 1.4 1.2 1.0 0.8 VIN = 2.7V VOUT = 10V 0.6 0.4 40 50 VIN = 2.7V VOUT = 12V 60 70 80 90 100 Output Current (mA) IPEAK = IOUT D * VIN(MIN) + MAX (1 - DMAX) (2 * FS * L) At light load and low output voltage, the controller reduces the operating frequency to maintain maximum operating efficiency. As a result, further reduction in output load does not reduce the peak current. Minimum peak current can be estimated from 0.5A to 0.75A. At high load and high output voltages, the switching frequency is somewhat diminished, resulting in higher IPEAK. Bench measurements are recommended to confirm actual IPEAK and ensure that the inductor does not saturate at maximum LED current and minimum input voltage. The RMS current flowing through the boost inductor is equal to the DC plus AC ripple components. Under worst-case RMS conditions, the current waveform is critically continuous. The resulting RMS calculation yields worst-case inductor loss. The RMS current value should be compared against the manufacturer's temperature rise, or thermal derating, guidelines. 19 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications IRMS = (wound and gapped) inductors. In general, chiptype inductors have increased winding resistance (DCR) when compared to shielded, wound varieties. IPEAK 3 For a given inductor type, smaller inductor size leads to an increase in DCR winding resistance and, in most cases, increased thermal impedance. Winding resistance degrades boost converter efficiency and increases the inductor's operating temperature. Inductor Efficiency Considerations The efficiency for different inductors is shown in Figure 7 for six white LEDs in series. Smaller inductors yield increased DCR and reduced operating efficiency. 80 To ensure high reliability, the inductor case temperature should not exceed 100C. In some cases, PCB heatsinking applied to the LIN node (nonswitching) can improve the inductor's thermal capability. PCB heatsinking may degrade EMI performance when applied to the SW node (switching) of the AAT1231/1231-1. Shielded inductors provide decreased EMI and may be required in noise sensitive applications. Unshielded chip inductors provide significant space savings at a reduced cost compared to shielded Manufacturer Sumida www.sumida.com Cooper Electronics www.cooperet.com Murata www.murata.com Taiyo Yuden www.t-yuden.com Efficiency (%) PLOSS(INDUCTOR) = IRMS2 * DCR 77 Cooper SD3814-2R2 (77m) Cooper SD3110-2R2 (161m) 74 71 Murata LQH2MCN2R2M02L (440m) 68 65 2 5 8 11 14 17 20 LED Current (mA) Figure 10: AAT1231/1231-1 Efficiency for Different Inductor Types (VIN = 3.6V; Six White LEDs in Series). Part Number Inductance (H) Maximum DC ISAT Current (mA) DCR ) (m Size (mm) LxWxH Type CDRH2D11-2R2 2.2 780 78 3.2x3.2x1.2 Shielded SD3814-2R2 SD3110-2R2 2.2 2.2 1900 910 77 161 4.0x4.0x1.4 3.1x3.1x1.0 Shielded Shielded LQH2MCN2R2M02L 2.2 455 440 2.0x1.6x0.7 Shielded NR3010T-2R2M 2.2 1100 95 3.0x3.0x1.0 CBC2016T2R2M 2.2 750 200 2.0x1.6x1.6 CBC2518T2R2M 2.2 510 90 2.5x1.8x1.8 Shielded Chip Non-Shielded Shielded Table 5: Recommended Inductors for Various Output Levels (Select IPEAK < ISAT). 20 1231.2006.08.1.1 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications Selecting the Boost Capacitors To maintain stable operation at full load, the output capacitor should be sized to maintain VOUT between 100mV and 200mV. The high output ripple inherent in the boost converter necessitates low impedance output filtering. The boost converter input current flows during both ON and OFF switching intervals. The input ripple current is less than the output ripple and, as a result, less input capacitance is required. Multi-layer ceramic (MLC) capacitors provide small size and adequate capacitance, low parasitic equivalent series resistance (ESR) and equivalent series inductance (ESL), and are well suited for use with the AAT1231/1231-1 boost regulator. MLC capacitors of type X7R or X5R are recommended to ensure good capacitance stability over the full operating temperature range. PCB Layout Guidelines Boost converter performance can be adversely affected by poor layout. Possible impact includes high input and output voltage ripple, poor EMI performance, and reduced operating efficiency. Every attempt should be made to optimize the layout in order to minimize parasitic PCB effects (stray resistance, capacitance, and inductance) and EMI coupling from the high frequency SW node. A suggested PCB layout for the AAT1231/1231-1 boost converter is shown in Figures 10 and 11. The following PCB layout guidelines should be considered: The output capacitor is sized to maintain the output load without significant voltage droop (VOUT) during the power switch ON interval, when the output diode is not conducting. A ceramic output capacitor from 2.2F to 4.7F is recommended (see Table 5). Typically, 25V rated capacitors are required for the 24V maximum boost output. Ceramic capacitors sized as small as 0805 are available which meet these requirements. 1. Minimize the distance from Capacitor C1 and C2 negative terminal to the PGND pins. This is especially true with output capacitor C2, which conducts high ripple current from the output diode back to the PGND pins. 2. Minimize the distance between L1 to DS1 and switching pin SW; minimize the size of the PCB area connected to the SW pin. 3. Maintain a ground plane and connect to the IC PGND pin(s) as well as the GND terminals of C1 and C2. 4. Consider additional PCB area on DS1 cathode to maximize heatsinking capability. This may be necessary when using a diode with a high VF and/or thermal resistance. MLC capacitors exhibit significant capacitance reduction with applied voltage. Output ripple measurements should confirm that output voltage droop and operating stability are acceptable. Voltage derating can minimize this factor, but results may vary with package size and among specific manufacturers. Output capacitor size can be estimated at a switching frequency (FS) of 500kHz (worst case). COUT = Manufacturer Murata Murata Murata Murata Murata IOUT * DMAX FS * VOUT Part Number Value (F) Voltage Rating Temp Co Case Size GRM188R60J225KE19 GRM188R61A225KE34 GRM219R61E225KA12 GRM21BR71E225KA73L GRM21BR61E475KA12 2.2 2.2 2.2 2.2 4.7 6.3 10 25 25 25 X5R X5R X5R X7R X5R 0603 0603 0805 0805 0805 Table 6: Recommended Ceramic Capacitors. 1231.2006.08.1.1 21 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications AAT1231/1231-1 White LED Driver S2Cwire Microcontroller Figure 11: AAT1231/1231-1 Evaluation Board Top Side Layout (with six LEDs and microcontroller). 22 Figure 12: AAT1231/1231-1 Evaluation Board Bottom Side Layout (with six LEDs and microcontroller). 1231.2006.08.1.1 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications VCC R7 1K R8 330 R6 1K R5 1K D7 RED 1 3 5 Down 02 4 1 3 5 Select 02 4 1 3 5 C3 1F U2 1 02 4 Up SW3 2 3 4 SW2 S2Cwire Microcontroller VDD GP5 GP4 GP3 VSS GP0 GP1 GP2 8 7 6 R9 330 5 PIC12F675 D8 GREEN (Select indicator) SW1 R4 10K J2 DC- J3 DC+ DS1 Schottky L1 J1 1 2 3 2.2H U1 VCC 1 JP1 2 3 4 C1 2.2F 5 6 VIN EN SEL VP N/C SW LIN OVP FB GND PGND SW VOUT R2 226K 12 11 10 R3 12K 9 8 7 AAT1231/1231-1 R1 D6 D5 30.1 LED LED D1 LED AAT1231/1231-1 White LED Driver D2 LED D3 LED C2 2.2F D4 LED U1 AnalogicTech AAT1231/1231-1 TSOPJW-12 package U2 PIC12F675 C1 GRM188R60J225KE01 C2 GRM21BR71E225KA73 C3 GRM216R61A105KA01 R1 30.1, 1%, 1/4W; 0603 R2 226k, 1%, 1/4W; 0603 R3 12.1k, 1%, 1/4W; 0603 R4 10k, 5%, 1/4W; 0603 R5, R6, R7 1K, 5%, 1/4W; 0805 R8, R9 330, 5%, 1/4W; 0805 JP1 0, 5%; 0805 DS1 BAT42W L1 Cooper Electronics 2.2H SD3814-2R2 D1-D6 White Hyper-Bright LED LW M673 D7 Red LED 1206 D8 Green LEC 1206 SW1 - SW3 SPST, 5mm J1, J2, J3 Conn. Header, 2mm Figure 13: AAT1231/1231-1 Evaluation Board Schematic (with six LEDs and microcontroller). 1231.2006.08.1.1 23 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications Additional Applications Efficiency vs. LED Current L = 2.2H C1 2.2F PVIN LIN VIN SW R2 187k C2 2.2F OVP R3 12k ENSET SEL 85 FB AGND VIN = 5V 84 AAT1231/ 1231-1 PGND (4 White LEDs; RBALLAST = 30.1 ) Up to 24V/ 50mA max Efficiency (%) Li-Ion VIN = 2.7V to 5.5V DS1 83 82 81 80 VIN = 4.2V VIN = 3.6V 79 78 30.1 20mA 77 2 4 6 8 10 12 14 16 18 20 18 20 LED Current (mA) Figure 14: Four LEDs In Series Configuration. Efficiency vs. LED Current (5 White LEDs; RBALLAST = 30.1 ) L = 2.2H C1 2.2F LIN VIN SW 82 AAT1231/ 1231-1 PGND DS1 R2 196k OVP R3 12k ENSET SEL AGND 83 C2 2.2F Efficiency (%) Li-Ion VIN = 2.7V to 5.5V PVIN Up to 24V/ 50mA max VIN = 5V 81 80 VIN = 4.2V 79 VIN = 3.6V 78 77 76 FB 30.1 20mA 75 2 4 6 8 10 12 14 16 LED Current (mA) Figure 15: Five LEDs In Series Configuration. 24 1231.2006.08.1.1 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications Efficiency vs. LED Current L = 2.2H C1 2.2F LIN VIN SW (6 White LEDs; RBALLAST = 30.1 ) Up to 24V/ 50mA max 81 AAT1231/ 1231-1 R2 226k 80 C2 2.2F Efficiency (%) Li-Ion VIN = 2.7V to 5.5V PVIN DS1 OVP PGND R3 12k EN/SET SEL AGND FB 30.1 VIN = 5V 79 78 VIN = 4.2V 77 76 VIN = 3.6V 75 74 20mA 73 2 4 6 8 10 12 14 16 18 20 LED Current (mA) Figure 16: Six LEDs In Series Configuration. L = 2.2H C1 2.2F PVIN LIN VIN SW Efficiency vs. LED Current Up to 24V/ 50mA max (12 White LEDs; RBALLAST = 30.1 ) 84 AAT1231/ 1231-1 R2 226k 83 C2 2.2F OVP PGND R3 12k EN/SET SEL AGND FB 30.1 VIN = 5V 82 Efficiency (%) Li-Ion VIN = 2.7V to 5.5V DS1 81 80 79 VIN = 4.2V 78 77 VIN = 3.6V 76 20mA 75 30.1 20mA 74 2 4 6 8 10 12 14 16 18 20 LED Current (mA) Figure 17: Twelve LEDs In Series/Parallel Configuration. 1231.2006.08.1.1 25 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications Ordering Information Package Marking1 Part Number (Tape and Reel)2 TSOPJW-12 TSOPJW-12 SDXYY TUXYY AAT1231ITP-T1 AAT1231ITP-1-T1 All AnalogicTech products are offered in Pb-free packaging. The term "Pb-free" means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/pbfree. Package Information TSOPJW-12 2.85 0.20 + 0.10 - 0.05 2.40 0.10 0.20 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 7 NOM 0.04 REF 0.055 0.045 0.15 0.05 + 0.10 1.00 - 0.065 0.9625 0.0375 3.00 0.10 4 4 0.45 0.15 0.010 2.75 0.25 All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 26 1231.2006.08.1.1 AAT1231/1231-1 Step-Up DC/DC Converters for White LED Backlight Applications (c) Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech's standard warranty. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders. Advanced Analogic Technologies, Inc. 830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 1231.2006.08.1.1 27