LT3496 Triple Output LED Driver Features Description True Color PWM™ Dimming Delivers Up to 3000:1 Dimming Ratio n Built-In Gate Driver for PMOS LED Disconnect n Three Independent Driver Channels with 750mA, 45V Internal Switches n Operates in Buck, Boost, Buck-Boost Modes n CTRL Pin Accurately Sets LED Current Sense Threshold Over a Range of 10mV to 100mV n Adjustable Frequency: 330kHz to 2.1MHz n Open LED Protection n Wide V Supply Range: IN Operation from 3V to 30V Transient Protection to 40V n Surface Mount Components n 28-Lead (4mm × 5mm) QFN and TSSOP Packages The LT®3496 is a triple output DC/DC converter designed to operate as a constant-current source and is ideal for driving LEDs. The LT3496 works in buck, boost or buckboost mode. The LT3496 uses a fixed frequency, current mode architecture resulting in stable operation over a wide range of supply and output voltages. A frequency adjust pin allows the user to program switching frequency between 330kHz and 2.1MHz to optimize efficiency and external component size. n The LT3496 supports 3000:1 dimming control on each channel. Each of the three regulators is independently operated by that channel’s PWM signal. The PWM feature allows precise adjustment of the color mixing or dimming ratio of the LED source. Each of the three channels has a built-in gate driver to drive an external LED-disconnect P-channel MOSFET, allowing high dimming range. The output current range of each channel of the LT3496 is programmed with an external sense resistor. Applications n n n n RGB Lighting Billboards and Large Displays Automotive and Avionic Lighting Constant-Current Sources The CTRL pins are used to adjust the LED currents either for analog dimming or overtemperature protection. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and ThinSOT and True Color PWM are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 7199560, 7321203, and others pending. Typical Application High Dimming Ratio Triple Output LED Power Supply PVIN 42V CAP1 CAP2 CAP3 200mΩ 200mΩ 200mΩ LED1 LED2 LED3 TG1 0.5A 18µH 0.47µF 0.47µF SW1 VIN 3V TO 24V 1µF PWM1, PWM2, PWM3 SHDN CAP1, CAP2, CAP3 LED1, LED2, LED3 VIN PWM1, PWM2, PWM3 SHDN 3000:1 PWM Dimming at 120Hz TG3 TG2 7 LEDs 1µF s3 0.5A 18µH SW2 LT3496 GND PWM 5V/DIV 0.5A 18µH IL 0.5A/DIV ILED 0.5A/DIV 0.47µF 0.5µs/DIV SW3 TG1, TG2, TG3 VC1, VC2, VC3 VREF CTRL1, CTRL2, CTRL3 fADJ OVP1, OVP2, OVP3 3496 TA01b 22k 470pF 3496 TA01a 3496ff LT3496 Absolute Maximum Ratings (Note 1) VIN (Note 4)................................................................40V SW1, SW2, SW3, LED1, LED2, LED3, CAP1, CAP2, CAP3....................................................45V TG1, TG2, TG3..................................... CAP – 10V to CAP PWM1, PWM2, PWM3...............................................20V VREF , CTRL1, CTRL2, CTRL3, fADJ, VC1, VC2, VC3, OVP1, OVP2, OVP3...................................................2.5V SHDN (Note 4)............................................................VIN Operating Junction Temperature Range (Notes 2, 6) LT3496E............................................. –40°C to 125°C LT3496I.............................................. –40°C to 125°C LT3496H............................................. –40°C to 150°C Storage Temperature Range QFN..................................................... –65°C to 150°C TSSOP.................................................. 65°C to 125°C Lead Temperature (Soldering, 10 sec) TSSOP............................................................... 300°C Pin Configuration TOP VIEW TOP VIEW 26 LED3 PWM1 4 25 CAP3 VREF 5 24 SW3 CTRL3 6 CTRL2 7 CTRL1 8 fADJ 9 20 TG2 fADJ 6 VC3 10 19 SW1 VC3 7 16 SW1 VC2 11 18 CAP1 VC2 8 15 CAP1 VC1 12 17 LED1 28 27 26 25 24 23 PWM1 1 22 CAP3 21 SW3 23 SW2 VREF 2 CTRL3 3 20 SW2 22 CAP2 CTRL2 4 21 LED2 CTRL1 5 FE PACKAGE 28-LEAD PLASTIC TSSOP θJA = 30°C/W, θJC = 10°C/W EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB LED1 TG1 OVP1 15 OVP1 9 10 11 12 13 14 OVP2 16 TG1 OVP2 14 18 LED2 17 TG2 VC1 OVP3 13 19 CAP2 29 OVP3 29 LED3 27 TG3 3 TG3 2 PWM2 VIN PWM3 SHDN 28 VIN PWM3 1 PWM2 SHDN UFD PACKAGE 28-LEAD (4mm s 5mm) PLASTIC QFN θJA = 34°C/W, θJC = 2.7°C/W EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3496EFE#PBF LT3496EFE#TRPBF 3496FE 28-Lead Plastic TSSOP –40°C to 125°C LT3496IFE#PBF LT3496IFE#TRPBF 3496FE 28-Lead Plastic TSSOP –40°C to 125°C LT3496EUFD#PBF LT3496EUFD#TRPBF 3496 28-Lead (4mm × 5mm) Plastic QFN –40°C to 125°C LT3496IUFD#PBF LT3496IUFD#TRPBF 3496 28-Lead (4mm × 5mm) Plastic QFN –40°C to 125°C LT3496HUFD#PBF LT3496HUFD#TRPBF 3496 28-Lead (4mm × 5mm) Plastic QFN –40°C to 150°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. *For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 3496ff LT3496 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VSHDN = 5V, CAP1, CAP2, CAP3 = 5V, PWM1, PWM2, PWM3 = 5V, fADJ = 0.5V, CTRL1, CTRL2, CTRL3 = 1.5V, OVP1, OVP2, OVP3 = 0V, unless otherwise noted. PARAMETER CONDITIONS VIN Operation Voltage (Note 4) MIN VIN Undervoltage Lockout Full-Scale LED Current Sense Voltage (VCAP1-LED1, VCAP2-LED2, VCAP3-LED3) CAP1, CAP2, CAP3 = 24V One-Tenth Scale LED Current Sense Voltage (VCAP1-LED1, VCAP2-LED2, VCAP3-LED3) CTRL1, CTRL2, CTRL3 = 100mV, CAP1, CAP2, CAP3 = 24V H-Grade E-Grade, I-Grade CAP1, CAP2, CAP3 Operating Voltage 0V ≤ VCAP1-LED1 ≤ 104mV 0V ≤ VCAP2-LED2 ≤ 104mV 0V ≤ VCAP3-LED3 ≤ 104mV VREF Output Voltage IREF = 200µA, Current Out of Pin VREF Line Regulation 3V ≤ VIN ≤ 40V, IREF = 10µA Quiescent Current in Shutdown SHDN = 0V Quiescent Current Idle PWM1, PWM2, PWM3 = 0V TYP 3 MAX UNITS 30 V 2.1 2.4 V 98 97 100 l 103 104 mV mV l l 7.5 7.5 10 10 13.5 12.5 mV mV 2.5 l 1.96 Quiescent Current Active (Not Switching) 45 V 2.04 V 0.03 %/V 0.1 10 µA 6 7.5 mA 2 11 14 mA 1900 2100 1300 330 2300 kHz kHz kHz 70 78 87 97 Switching Frequency fADJ = 1.5V fADJ = 0.5V fADJ = 0.1V Maximum Duty Cycle fADJ = 1.5V (2.1MHz) fADJ = 0.5V (1.3MHz) fADJ = 0.1V (330kHz) CTRL1, CTRL2, CTRL3 Input Bias Current Current Out of Pin, CTRL1, CTRL2, CTRL3 = 0.1V 20 100 nA fADJ Input Bias Current Current Out of Pin, fADJ = 0.1V 20 100 nA OVP1, OVP2, OVP3 Input Bias Current Current Out of Pin, OVP1, OVP2, OVP3 = 0.1V 10 100 nA 0.95 1 1.05 V –20 0 20 nA OVP1, OVP2, OVP3 Threshold l % % % VC1, VC2, VC3 Idle Input Bias Current PWM1, PWM2, PWM3 = 0V VC1, VC2, VC3 Output Impedance CAP1, CAP2, CAP3 = 24V 10 MΩ EAMP gm (ΔIVC/ΔVCAP-LED) CAP1, CAP2, CAP3 = 24V 200 µS SW1, SW2, SW3 Current Limit (Note 3) SW1, SW2, SW3 VCESAT ISW = 500mA (Note 3) SW1, SW2, SW3 Leakage Current SHDN = 0V, SW = 5V CAP1, CAP2, CAP3 Input Bias Current 750 1000 1250 260 mV 2 180 mA µA 250 µA CAP1, CAP2, CAP3, LED1, LED2, LED3 Idle Input Bias Current PWM1, PWM2, PWM3 = 0V 1 µA CAP1, CAP2, CAP3, LED1, LED2, LED3 Input Bias Current in Shutdown SHDN = 0V 1 µA 3496ff LT3496 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VSHDN = 5V, CAP1, CAP2, CAP3 = 5V, PWM1, PWM2, PWM3 = 5V, fADJ = 0.5V, CTRL1, CTRL2, CTRL3 = 1.5V, OVP1, OVP2, OVP3 = 0V, unless otherwise noted. PARAMETER CONDITIONS MIN TYP SHDN Input Low Voltage 0.4 SHDN Input High Voltage SHDN Pin Current MAX 1.5 VSHDN = 5V, Current Into Pin V V 65 PWM1, PWM2, PWM3 Input Low Voltage PWM1, PWM2, PWM3 Input High Voltage UNITS 100 µA 0.4 V 1.2 V PWM1, PWM2, PWM3 Pin Current Current Into Pin 160 210 µA Gate Off Voltage (CAP1 – TG1, CAP2 – TG2, CAP3 – TG3) CAP1, CAP2, CAP3 = 40V, PWM1, PWM2, PWM3 = 0V 0.1 0.3 V Gate On Voltage (CAP1 – TG1, CAP2 – TG2, CAP3 – TG3) CAP1, CAP2, CAP3 = 40V 6.5 7.5 V Gate Turn-On Delay CLOAD = 300pF, CAP1, CAP2, CAP3 = 40V (Note 5) 110 ns Gate Turn-Off Delay CLOAD = 300pF, CAP1, CAP2, CAP3 = 40V (Note 5) 110 ns Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LT3496E is guaranteed to meet performance specifications from 0°C to 125°C junction temperature. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3496I is guaranteed over the full –40°C to 125°C operating junction temperature range. The LT3496H is guaranteed over the full –40°C to 150°C operating junction temperature range. High junction temperatures degrade operating lifetimes. Operating lifetime is derated at junction temperatures greater than 125°C. 5.5 Note 3: Current flows into pin. Current limit and switch VCESAT is guaranteed by design and/or correlation to static test. Note 4: Absolute maximum voltage at the VIN and SHDN pins is 40V for nonrepetitive 1 second transients, and 30V for continuous operation. Note 5: Gate turn-on/turn-off delay is measured from 50% level of PWM voltage to 90% level of gate on/off voltage. Note 6: The LT3496 includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed the maximum operating junction temperature when overtemperature protection is active. Continuous operating above the specified maximum operating junction temperature may impair device reliability. 3496ff LT3496 Typical Performance Characteristics Quiescent Current 1000 10 400 800 8 PWM1, PWM2, PWM3 = 0V 6 4 SWITCH CURRENT LIMIT (mA) SWITCH VOLTAGE (mV) INPUT CURRENT (mA) 500 PWM1, PWM2, PWM3 = 5V 12 300 200 100 2 VC = GND, NOT SWITCHING 0 10 20 30 0 40 0 200 VIN (V) 600 800 400 SWITCH CURRENT (mA) 3496 G01 200 0 1000 800 2250 2.03 2000 2.02 1750 VREF (V) 2.00 3496 G04 1.96 –50 –25 100 1000 1.97 25 50 75 100 125 150 TEMPERATURE (°C) 80 1500 1.98 200 60 40 DUTY CYCLE (%) 1250 1.99 400 20 Switch Frequency vs fADJ 2.04 2.01 600 0 3496 G03 SWITCH FREQUENCY (kHz) 1000 0 400 Reference Voltage vs Temperature 1200 0 –50 –25 600 3496 G02 Switch Current Limit vs Temperature CURRENT LIMIT (mA) Switch Current Limit vs Duty Cycle Switch On Voltage 14 0 (TA = 25°C unless otherwise noted) 750 500 250 0 25 50 75 100 125 150 TEMPERATURE (°C) 3496 G05 0 0 0.2 0.4 0.6 fADJ (V) 0.8 1.0 1.2 3496 G06 3496ff LT3496 Typical Performance Characteristics Switch Frequency vs Temperature 120 fADJ = 1.2V 2.2 2.1 2.0 VCAP = 24V 1.8 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 80 60 40 0 0 101 100 99 0.2 0.4 0.6 0.8 CTRL (V) 1 1.2 97 0 10 20 30 VCAP (V) 40 50 3496 G09 3496 G08 VCAP-LED Threshold vs Temperature VCAP-LED THRESHOLD (mV) CTRL = 1.2V 98 3496 G07 102 VCAP-LED Threshold vs VCAP 102 20 1.9 103 103 100 VCAP-LED THRESHOLD (mV) SWITCH FREQUENCY (MHz) 2.3 VCAP-LED Threshold vs CTRL VCAP-LED TRHESHOLD (mV) 2.4 (TA = 25°C unless otherwise noted) PMOS Turn On Waveforms PMOS Turn Off Waveforms CTRL = 1.2V VCAP = 24V 5V 5V PWM 101 PWM 0V 0V 100 40V 99 TG 30V 98 97 –50 –25 40V TG 0 25 50 75 100 125 150 TEMPERATURE (°C) 30V VCAP = 40V 200ns/DIV 3496 G11 VCAP = 40V 200ns/DIV 3496 G12 3496 G10 3496ff LT3496 Pin Functions PWM1, PWM2, PWM3: Pulse Width Modulated Inputs. Signal low turns off the respective converter, reduces quiescent supply current and causes the VC pin for that converter to become high impedance. PWM pin must not be left floating; tie to VREF if not used. When the PWM pin is low, the TG pin pulls up to CAP to turn off the external MOSFET. When the PWM pin is high, the external MOSFET turns on. Respective CAP-TG is limited to 6.5V to protect the MOSFET. Leave open if the external MOSFET is not used. VREF: Reference Output Pin. Can supply up to 200µA. The nominal Output Voltage is 2V. LED1, LED2, LED3: Noninverting Inputs of Current Sense Error Amplifiers. Connect directly to LED current sense resistor terminal for current sensing of the respective converter CTRL1, CTRL2, CTRL3: LED Current Adjustment Pins. Sets voltage across external sense resistor between CAP and LED pins of the respective converter. Setting CTRL voltage to be less than 1V will control the current sense voltage to be one-tenth of CTRL voltage. If CTRL voltage is higher than 1V, the default current sense voltage is 100mV. The CTRL pin must not be left floating. fADJ: Switching Frequency Adjustment Pin. Setting fADJ voltage to be less than 1V will adjust switching frequency up to 2.1MHz. If fADJ voltage is higher than 1V, the default switching frequency is 2.1MHz. The fADJ pin must not be left floating. VC1, VC2, VC3: Error Amplifier Compensation Pins. Connect a series RC from these pins to GND. CAP1, CAP2, CAP3: Inverting Inputs of Current Sense Error Amplifiers. Connect directly to other terminal of LED current sense resistor terminal of the respective converter. SW1, SW2, SW3: Switch Pins. Collector of the internal NPN power switch of the respective converter. Connect to external inductor and anode of external Schottky rectifier of the respective converter. Minimize the metal trace area connected to this pin to minimize electromagnetic interference. VIN: Input Supply Pin. Must be locally bypassed. Powers the internal control circuitry. OVP1, OVP2, OVP3: Open LED Protection Pins. A voltage higher than 1V on OVP turns off the internal main switch of the respective converter. Tie to ground if not used. SHDN: Shutdown Pin. Used to shut down the switching regulator and the internal bias circuits for all three converters. Tie to 1.5V or greater to enable the device. Tie below 0.4V to turn off the device. TG1, TG2, TG3: The Gate Driver Output Pins for Disconnnect P‑Channel MOSFETs. One for each converter. Exposed Pad: Signal Ground and Power Ground. Solder paddle directly to ground plane. 3496ff LT3496 Block Diagram D1 VSENSE + – ILED M1 C2 LED1 L1 VIN C1 RSENSE 0.2Ω CAP1 R3 LED1 TG1 OVP1 – RC + V1 A1 – + + – 1V NPN DRIVER A6 A4 VC A8 + – R1 2k 1V CTRL1 EAMP + PWM1 CC SW1 MOSFET DRIVER VC1 R4 PWM1 A7 Q3 SLOPE Q1 SR LATCH – + CTRL BUFFER A5 A3 R A2 PWM COMPARATOR Q S ISENS2 + A10 R2 20k – GND REPLICATED FOR EACH CHANNEL VIN VIN C3 SHDN INTERNAL REGULATOR AND UVLO VIN ISRC 200µA VREF RAMP GENERATOR – 2V REFERENCE + A9 Q2 OSCILLATOR fADJ SHARED COMPONENTS R5 C4 3496 BD R6 Figure 1. LT3496 Block Diagram Working in Boost Configuration 3496ff LT3496 Applications Information Operation The LT3496 uses a fixed frequency, current mode control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the Block Diagram in Figure 1. The oscillator, ramp generator, reference, internal regulator and UVLO are shared among the three converters. The control circuitry, power switch etc., are replicated for each of the three converters. Figure 1 shows the shared circuits and only converter 1 circuits. If the SHDN pin is tied to ground, the LT3496 is shut down and draws minimal current from VIN. If the SHDN pin exceeds 1.5V, the internal bias circuits turn on. The switching regulators start to operate when their respective PWM signal goes high. The main control loop can be understood by following the operation of converter 1. The start of each oscillator cycle sets the SR latch, A3, and turns on power switch Q1. The signal at the noninverting input (SLOPE node) of the PWM comparator A2 is proportional to the sum of the switch current and oscillator ramp. When SLOPE exceeds VC1 (the output of the error amplifier A1), A2 resets the latch and turns off the power switch Q1 through A4 and A5. In this manner, A10 and A2 set the correct peak current level to keep the output in regulation. Amplifier A8 has two noninverting inputs, one from the 1V internal voltage reference and the other one from the CTRL1 pin. Whichever input is lower takes precedence. A8, Q3 and R1 force V1, the voltage across R1, to be one tenth of either 1V or the voltage of CTRL1 pin, whichever is lower. VSENSE is the voltage across the sensing resistor, RSENSE, which is connected in series with the LEDs. VSENSE is compared to V1 by A1. If VSENSE is higher than V1, the output of A1 will decrease, thus reducing the amount of current delivered to LEDs. In this manner the current sensing voltage VSENSE is regulated to V1. Converters 2 and 3 are identical to converter 1. PWM Dimming Control LED1 can be dimmed with pulse width modulation using the PWM1 pin and an external P-channel MOSFET, M1. If the PWM1 pin is pulled high, M1 is turned on by internal driver A7 and converter 1 operates nominally. A7 limits CAP1-TG1 to 6.5V to protect the gate of M1. If the PWM1 pin is pulled low, Q1 is turned off. Converter 1 stops operating, M1 is turned off, disconnects LED1 and stops current draw from output capacitor C2. The VC1 pin is also disconnected from the internal circuitry and draws minimal current from the compensation capacitor CC. The VC1 pin and the output capacitor store the state of the LED1 current until PWM1 is pulled up again. This leads to a highly linear relationship between pulse width and output light, and allows for a large and accurate dimming range. A P-channel MOSFET with smaller total gate charge (QG) improves the dimming performance, since it can be turned on and off faster. Use a MOSFET with a QG lower than 10nC, and a minimum VTH of –1V to –2V. Don’t use a Low VTH PMOS. To optimize the PWM control of all the three channels, the rising edge of all the three PWM signals should be synchronized. In the applications where high dimming ratio is not required, M1 can be omitted to reduce cost. In these conditions, TG1 should be left open. The PWM dimming range can be further increased by using CTRL1 pin to linearly adjust the current sense threshold during the PWM1 high state. Loop Compensation Loop compensation determines the stability and transient performance. The LT3496 uses current mode control to regulate the output, which simplifies loop compensation. To compensate the feedback loop of the LT3496, a series resistor-capacitor network should be connected from the VC pin to GND. For most applications, the compensation capacitor should be in the range of 100pF to 1nF. The compensation resistor is usually in the range of 5k to 50k. To obtain the best performance, tradeoffs should be made in the compensation network design. A higher value of compensation capacitor improves the stability and dimming range (a larger capacitance helps hold the VC voltage when the PWM signal is low). However, a large compensation capacitor also increases the start-up time and the time to recover from a fault condition. Similarly, a larger compensation resistor improves the transient response but may reduce the phase margin. A practical approach is to start with one of the circuits in this data sheet that is similar to your application and tune the compensation network to optimize the performance. The stability, PWM 3496ff LT3496 Applications Information dimming waveforms and the start-up time should be checked across all operating conditions. Open-LED Protection Input Capacitor Selection For proper operation, it is necessary to place a bypass capacitor to GND close to the VIN pin of the LT3496. A 1µF or greater capacitor with low ESR should be used. A ceramic capacitor is usually the best choice. The LT3496 has open-LED protection for all the three converters. As shown in Figure 1, the OVP1 pin receives the output voltage (the voltage across the output capacitor) feedback signal from an external resistor divider. OVP1 voltage is compared with a 1V internal voltage reference by comparator A6. In the event the LED string is disconnected or fails open, converter 1 output voltage will increase, causing OVP1 voltage to increase. When OVP1 voltage exceeds 1V, the power switch Q1 will turn off, and cause the output voltage to decrease. Eventually, OVP1 will be regulated to 1V and the output voltage will be limited. In the event one of the converters has an open-LED protection, the other converters will continue functioning properly. where D is the switch duty cycle. A 1µF ceramic type capacitor placed close to the Schottky diode and the ground plane is usually sufficient for each channel. Switching Frequency and Soft-Start Output Capacitor Selection The LT3496 switching frequency is controlled by fADJ pin voltage. Setting fADJ voltage to be less than 1V will reduce switching frequency. If fADJ voltage is higher than 1V, the default switching frequency is 2.1MHz. In general, a lower switching frequency should be used where either very high or very low switch duty cycle is required or higher efficiency is desired. Selection of a higher switching frequency will allow use of low value external components and yield a smaller solution size and profile. Connecting fADJ pin to a lowpass filter (R5 and C4 in Figure 1) from the REF pin provides a soft-start function. During start-up, fADJ voltage increases slowly from 0V to the setting voltage. As a result, the switching frequency increases slowly to the setting frequency. This function limits the inrush current during start-up. Undervoltage Lockout The LT3496 has an undervoltage lockout circuit that shuts down all the three converters when the input voltage drops below 2.4V. This prevents the converter from switching in an erratic mode when powered from a low supply voltage. In the buck mode configuration, the capacitor at PVIN has large pulsed currents due to the current returned though the Schottky diode when the switch is off. For the best reliability, this capacitor should have low ESR and ESL and have an adequate ripple current rating. The RMS input current is: IIN(RMS) =ILED • (1– D) • D The selection of output filter capacitor depends on the load and converter configuration, i.e., step-up or step-down. For LED applications, the equivalent resistance of the LED is typically low, and the output filter capacitor should be large enough to attenuate the current ripple. To achieve the same LED ripple current, the required filter capacitor value is larger in the boost and buck-boost mode applications than that in the buck mode applications. For the LED buck mode applications, a 0.22µF ceramic capacitor is usually sufficient for each channel. For the LED boost and buck-boost applications, a 1µF ceramic capacitor is usually sufficient for each channel. If higher LED current ripple can be tolerated, a lower output capacitance can be selected to reduce the capacitor’s cost and size. Use only ceramic capacitors with X7R or X5R dielectric, as they are good for temperature and DC bias stability of the capacitor value. All ceramic capacitors exhibit loss of capacitance value with increasing DC voltage bias, so it may be necessary to choose a higher value capacitor to get the required capacitance at the operation voltage. Always check that the voltage rating of the capacitor is sufficient. Table 1 shows some recommended capacitor vendors. 3496ff 10 LT3496 Applications Information Table 2. Surface Mount Inductors Table 1. Ceramic Capacitor Manufacturers VENDOR TYPE SERIES Taiyo Yuden Ceramic X5R, X7R AVX Ceramic X5R, X7R Murata Ceramic X5R, X7R Kemet Ceramic X5R, X7R VALUE (µH) DCR (Ω MAX) IRMS (A) SIZE W × L × H (mm3) CMD4D06 2.2 0.116 0.95 3.5 × 4.3 × 0.8 3.3 0.174 0.77 CDRH3D16 2.2 0.072 1.20 3.3 0.085 1.10 4.7 0.105 0.90 CDRH4D28 10 0.128 1.00 15 0.149 0.76 CDRH5D28 22 0.122 0.9 33 0.189 0.75 2.2 0.140 0.97 3.3 0.165 0.90 4.7 0.246 0.74 SD14 10 0.2058 1.1 5.0 × 5.0 × 1.4 SD20 15 0.1655 1.25 5.0 × 5.0 × 2.0 22 0.2053 1.12 33 0.2149 1.11 5.0 × 5.0 × 2.5 2.2 0.06 1.48 3.0 × 3.0 × 1.5 4.7 0.12 1.02 4.7 0.075 1.6 10 0.100 1.2 15 0.180 0.95 22 0.210 0.77 PART NUMBER Sumida Inductor Selection Several inductors that work well with the LT3496 are listed in Table 2. However, there are many other manufacturers and devices that can be used. Consult each manufacturer for more detailed information and their entire range of parts. Ferrite core inductors should be used to obtain the best efficiency. Choose an inductor that can handle the necessary peak current without saturating, and ensure that the inductor has a low DCR (copper-wire resistance) to minimize I2R power losses. An inductor with a magnetic shield should be used to prevent noise radiation and cross coupling among the three channels. SD3112 SD25 The Schottky diode conducts current during the interval when the switch is turned off. Select a diode VR rated for the maximum SW voltage. It is not necessary that the forward current rating of the diode equal the switch current limit. The average current, IF , through the diode is a function of the switch duty cycle. Select a diode with forward current rating of: Taiyo Yuden where IL is the inductor current. If using the PWM feature for dimming, it is important to consider diode leakage, which increases with the temperature from the output during the PWM low interval. Therefore, choose the Schottky diode with sufficient low leakage current. Table 3 shows several Schottky diodes that work well with the LT3496. 5.0 × 5.0 × 3.0 6.0 × 6.0 × 3.0 CooperET Diode Selection IF = IL • (1 – D) 3.8 × 3.8 × 1.8 NR3015 NP04SZB 3.1 × 3.1 × 1.2 4.0 × 4.0 × 1.8 Table 3. Schottky Diodes PART NUMBER VR (V) IF (A) PACKAGE ZLLS350 40 0.38 SOD523 ZLLS400 40 0.52 SOD323 ZETEX 3496ff 11 LT3496 Applications Information Programming the LED Current The LED current of each channel is programmed by connecting an external sense resistor RSENSE in series with the LED load, and setting the voltage regulation threshold across that sense resistor using CTRL input. If the CTRL voltage, VCTRL, is less than 1V, the LED current is: ILED = VCTRL 10 • RSENSE Board Layout If VCTRL is higher than 1V, the LED current is: ILED = 100mV RSENSE The CTRL pins should not be left open. The CTRL pin can also be used in conjunction with a PTC thermistor to provide overtemperature protection for the LED load as shown in Figure 2. 2V VREF voltages to ensure that a junction temperature of 125°C is not exceeded. This is especially important when operating at high ambient temperatures. The exposed pad on the bottom of the package must be soldered to a ground plane. This ground should then be connected to an internal copper ground plane with thermal vias placed directly under the package to spread out the heat dissipated by the LT3496. 45k 50k CTRL1 to CTRL3 5k PTC 3496 F02 Figure 2 Thermal Considerations The LT3496 is rated to a maximum input voltage of 30V for continuous operation, and 40V for nonrepetitive one second transients. Careful attention must be paid to the internal power dissipation of the LT3496 at higher input The high speed operation of the LT3496 demands careful attention to board layout and component placement. The exposed pad of the package is the only GND terminal of the IC and is important for thermal management of the IC. Therefore, it is crucial to achieve a good electrical and thermal contact between the exposed pad and the ground plane of the board. Also, in boost configuration, the Schottky rectifier and the capacitor between GND and the cathode of the Schottky are in the high frequency switching path where current flow is discontinuous. These elements should be placed so as to minimize the path between SW and the GND of the IC. To reduce electromagnetic interference (EMI), it is important to minimize the area of the SW node. Use the GND plane under SW to minimize interplane coupling to sensitive signals. To obtain good current regulation accuracy and eliminate sources of channel to channel coupling, the CAP and LED inputs of each channel of the LT3496 should be run as separate lines back to the terminals of the sense resistor. Any resistance in series with CAP and LED inputs should be minimized. Finally, the bypass capacitor on the VIN supply to the LT3496 should be placed as close as possible to the VIN terminal of the device. 3496ff 12 LT3496 Typical Applications Minimum BOM Buck Mode LED Driver PVIN 42V CAP1 CAP2 CAP3 330mΩ 330mΩ 330mΩ LED1 LED2 LED3 0.3A 0.3A 0.3A 7 LEDs C6 0.22µF C4 C5 0.22µF 0.22µF L1 15µH D1 SW1 VIN 3V C7 1µF PWM1, PWM2, PWM3 SHDN CAP1, CAP2, CAP3 LED1, LED2, LED3 VIN PWM1, PWM2, PWM3 SHDN D2 C1-C3 1µF s3 L2 15µH SW2 LT3496 GND L3 15µH D3 SW3 TG1, TG2, TG3 VC1, VC2, VC3 VREF CTRL1, CTRL2, CTRL3 fADJ OVP1, OVP2, OVP3 OPEN 22k 470pF 3496 TA07a C1-C3, C7: MURATA GRM31MR71H105KA88 C4-C6: MURATA GRM21BR71H224KA01 D1-D3: DIODES DFLS160 L1-L3: TAIYO YUDEN NP04SZB 150M 300:1 PWM Dimming at 120Hz Efficiency 100 PWM 5V/DIV PWM = 3V CTRL = 0V TO 1.2V 95 EFFICIENCY (%) IL 0.5A/DIV ILED 0.5A/DIV 5µs/DIV 3496 TA07b 90 85 80 75 0 50 100 150 200 ILED (mA) 250 300 3496 TA07c 3496ff 13 LT3496 TYPICAL APPLICATIONS Triple Boost 100mA × 10 LED Driver PVIN 12V C1 2.2µF L1 10µH L2 10µH D1 D2 CAP1 C2 1µF L3 10µH C3 1µF 1Ω TG2 OVP1 20k SW1 VIN 3V C5 1µF PWM1, PWM2, PWM3 SHDN 1Ω LED3 TG3 M2 825k 100mA CAP3 LED2 M1 10 LEDs C4 1µF 1Ω LED1 TG1 D3 CAP2 825k 10 LEDs 100mA OVP2 20k SW2 CAP1, CAP2, CAP3 LED1, LED2, LED3 VIN PWM1, PWM2, PWM3 SHDN M3 825k 10 LEDs OVP3 100mA 20k SW3 TG1, TG2, TG3 OVP1, OVP2, OVP3 VC1, VC2, VC3 VREF fADJ CTRL1, CTRL2, CTRL3 LT3496 GND 10k 470pF 3496 TA03a C1: MURATA GRM31MR71C225KA35 C2-C5: MURATA GRM31MR71H105KA88 D1-D3: DIODES DFLS160 L1-L3: TAIYO YUDEN NP04SZB 100M M1-M3: ZETEX ZXMP6A13F Efficiency vs PWM Duty Cycle 3000:1 PWM Dimming at 120Hz 95 CTRL = 2V 90 PWM 5V/DIV EFFICIENCY (%) 85 IL 0.5A/DIV ILED 0.1A/DIV 80 75 70 65 60 55 0.5µs/DIV 3496 TA03b 50 0 20 80 60 40 PWM DUTY CYCLE (%) 100 3496 TA03d 3496ff 14 LT3496 TYPICAL APPLICATIONS Dual Boost LED Driver PVIN 12V C1 2.2µF L1 10µH L2 10µH L3 10µH D1 D2 CAP1 C2 1µF C3 1µF 1Ω D3 CAP2 LED1 CAP3 C4 1µF 1Ω 1Ω LED2 LED3 M1 M2 825k 10 LEDs PWM SHDN 10 LEDs 20k SW1 TG1 VIN 3V TO 12V C5 1µF 825k OVP1 100mA SW2 CAP1, CAP2, CAP3 LED1, LED2, LED3 VIN PWM1, PWM2, PWM3 SHDN SW3 TG2 OVP1, OVP2, OVP3 TG3 VC1, VC2, VC3 VREF fADJ CTRL1, CTRL2, CTRL3 LT3496 GND OVP2-3 200mA 20k OPEN 10k 470pF 3496 TA04 C1: MURATA GRM31MR71C225KA35 C2-C5: MURATA GRM31MR71H105KA88 D1-D3: DIODES DFLS160 L1-L3: TAIYO YUDEN NP04SZB 100M M1, M2: ZETEX ZXMP6A13F Triple Boost 20mA × 8 LED Driver PVIN 5V C1 2.2µF L1 22µH L2 22µH D1 C2 1µF L3 22µH D2 CAP1 C3 1µF 5Ω TG2 M1 20mA PWM1, PWM2, PWM3 SHDN 8 LEDs 20k CAP1, CAP2, CAP3 LED1, LED2, LED3 VIN PWM1, PWM2, PWM3 SHDN C1: MURATA GRM31MR71C225KA35 C2-C5: MURATA GRM31MR71H105KA88 D1-D3: ZETEX ZLLS350 L1-L3: TAIYO YUDEN NP04SZB 220M M1-M3: ZETEX ZXMP6A13F LED3 TG3 M2 M3 825k OVP1 SW1 VIN 5V C5 1µF 5Ω LED2 825k 8 LEDs CAP3 C4 1µF 5Ω LED1 TG1 D3 CAP2 SW2 LT3496 GND 20mA 825k OVP2 8 LEDs 20k 20mA OVP3 20k SW3 TG1, TG2, TG3 OVP1, OVP2, OVP3 VC1, VC2, VC3 VREF CTRL1, CTRL2, CTRL3 82k 10k 470pF fADJ 20k 3496 TA08a 3496ff 15 LT3496 TYPICAL APPLICATIONS Buck-Boost Mode 300mA × 6 LED Driver PVIN 10V TO 16V C1 2.2µF 6 LEDs 300mA L1 10µH L2 10µH L3 10µH 825k M1 LED1 LED2 1Ω 1Ω CAP1 D1 C3 1µF CAP3 D3 C4 0.1µF C5 1µF C7 1µF PVIN SW3 TG1 SW2 CAP1, CAP2, CAP3 LED1, LED2, LED3 VIN PWM1, PWM2, PWM3 SHDN PWM SHDN C8 1µF C6 0.1µF PVIN PVIN SW1 VIN 3V TO 16V 1Ω CAP2 D2 C2 0.1µF OVP1-3 20k LED3 OVP1, OVP2, OVP3 TG1, TG2, TG3 VC1, VC2, VC3 VREF fADJ CTRL1, CTRL2, CTRL3 LT3496 GND OPEN 10k 470pF 3496 TA05 C1: MURATA GRM31MR71E225KA93 C2, C4, C6: MURATA GRM21BR71H104KA01B C3, C5, C7: MURATA GRM31MR71H105KA88 C8: MURATA GRM31MR71E105KA93 D1-D3: DIODES DFLS160 L1-L3: TAIYO YUDEN NP04SZB 100M M1: ZETEX ZXMP6A13F Triple Buck Mode LED Driver with Open LED Protection PVIN 12V TO 40V TG1 CAP1 CAP2 CAP3 200mΩ 200mΩ 200mΩ LED1 LED2 LED3 TG2 M1 M2 20k 0.5A C4 0.47µF 5.6k M4 OVP1 2k L1 10µH D1 SW1 VIN 3V TO 24V C7 1µF PWM1, PWM2, PWM3 SHDN 20k 0.5A C5 0.47µF D2 TG3 M3 20k 5.6k L2 10µH 0.5A M5 C1-C3, C7: MURATA GRM31MR71H105KA88 C4-C6: MURATA GRM188R71C474KA88 D1-D3: DIODES DFLS160 L1-L3: TAIYO YUDEN NP04SZB 100M M1-M3: ZETEX ZXMP6A13F M4-M6: PHILIPS BC858B 5.6k M6 OVP2 OVP1 2k SW2 CAP1, CAP2, CAP3 LED1, LED2, LED3 VIN PWM1, PWM2, PWM3 SHDN C1-C3 1µF s3 LT3496 GND 2k L3 10µH C6 0.47µF D3 SW3 TG1, TG2, TG3 OVP1, OVP2, OVP3 VC1, VC2, VC3 VREF fADJ CTRL1, CTRL2, CTRL3 22k 470pF 3496 TA02 3496ff 16 LT3496 Package Description FE Package 28-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663) exposed pad Variation EB 9.60 – 9.80* (.378 – .386) 4.75 (.187) 4.75 (.187) 28 2726 25 24 23 22 21 20 19 18 1716 15 6.60 p0.10 2.74 (.108) 4.50 p0.10 SEE NOTE 4 0.45 p0.05 EXPOSED PAD HEAT SINK ON BOTTOM OF PACKAGE 6.40 2.74 (.252) (.108) BSC 1.05 p0.10 0.65 BSC RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.50 – 0.75 (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN MILLIMETERS (INCHES) 3. DRAWING NOT TO SCALE 1 2 3 4 5 6 7 8 9 10 11 12 13 14 0.25 REF 1.20 (.047) MAX 0o – 8o 0.65 (.0256) BSC 0.195 – 0.30 (.0077 – .0118) TYP 0.05 – 0.15 (.002 – .006) FE28 (EB) TSSOP 0204 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE 3496ff 17 LT3496 Package Description UFD Package 28-Lead Plastic QFN (4mm × 5mm) (Reference LTC DWG # 05-08-1712 Rev B) 0.70 p0.05 4.50 p 0.05 3.10 p 0.05 2.50 REF 2.65 p 0.05 3.65 p 0.05 PACKAGE OUTLINE 0.25 p0.05 0.50 BSC 3.50 REF 4.10 p 0.05 5.50 p 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 p 0.10 (2 SIDES) 0.75 p 0.05 R = 0.05 TYP PIN 1 NOTCH R = 0.20 OR 0.35 s 45o CHAMFER 2.50 REF R = 0.115 TYP 27 28 0.40 p 0.10 PIN 1 TOP MARK (NOTE 6) 1 2 5.00 p 0.10 (2 SIDES) 3.50 REF 3.65 p 0.10 2.65 p 0.10 (UFD28) QFN 0506 REV B 0.200 REF 0.00 – 0.05 0.25 p 0.05 0.50 BSC BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WXXX-X). 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 3496ff 18 LT3496 Revision History (Revision history begins at Rev F) REV DATE DESCRIPTION PAGE NUMBER F 4/10 Added H-Grade and Revised Entire Data Sheet 1 through 20 3496ff Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 19 LT3496 Typical Application Triple Buck-Boost Mode 100mA × 6 LED Driver PVIN 10V TO 16V C1 2.2µF 6 LEDs 100mA L1 10µH L2 10µH LED1 1Ω CAP1 D1 M2 TG2 3.9M OVP2 100k CAP2 D2 C3 1µF C4 0.1µF LED3 1Ω CAP3 D3 C5 1µF SW2 CAP1, CAP2, CAP3 LED1, LED2, LED3 VIN PWM1, PWM2, PWM3 SHDN LT3496 GND 3.9M OVP3 100k C6 0.1µF PVIN PVIN PWM SHDN 3.9M 1Ω 100k SW1 3000:1 PWM Dimming at 120Hz PWM 5V/DIV M3 TG3 LED2 OVP1 C2 0.1µF 6 LEDs 100mA L3 10µH M1 TG1 VIN 3V TO 16V C8 1µF 6 LEDs 100mA C7 1µF IL 0.5A/DIV ILED 0.1A/DIV PVIN SW3 TG1, TG2, TG3 OVP1, OVP2, OVP3 VC1, VC2, VC3 VREF fADJ CTRL1, CTRL2, CTRL3 0.5µs/DIV 3496 TA06b 10k 470pF 3496 TA06 C1: MURATA GRM31MR71E225KA93 C2, C4, C6: MURATA GRM21BR71H104KA01B C3, C5, C7: MURATA GRM31MR71H105KA88 C8: MURATA GRM31MR71E105KA93 D1-D3: DIODES DFLS160 L1-L3: TAIYO YUDEN NP04SZB 100M M1-M3: ZETEX ZXMP6A13F Related Parts PART NUMBER DESCRIPTION COMMENTS LT1618 Constant Current, 1.4MHz, 1.5A Boost Converter VIN: 1.6V to 18V, VOUT(MAX) = 36V, IQ = 1.8mA, ISD < 1µA, 10-Pin MS Package LT3453 1MHz, 800mA Synchronous Buck-Boost High Power LED Driver VIN: 2.7V to 5.5V, VOUT(MAX) = 5.5V, IQ = 2.5mA, ISD < 6µA, QFN Package LT3466 Dual Constant Current, 2MHz, High Efficiency White LED Boost Regulator with Integrated Schottky Diode VIN: 2.7V to 24V, VOUT(MAX) = 40V, IQ = 5mA, ISD < 16µA, DFN Package LT3467/LT3467A 1.1A (ISW), 1.3MHz/2.1MHz, High Efficiency Step-Up DC/DC Converters with Integrated Soft-Start VIN: 2.4V to 16V, VOUT(MAX) = 40V, IQ = 1.2mA, ISD < 1µA, ThinSOT™ Package LT3474 Step-Down 1A 2MHz LED Driver VIN: 4V to 36V, VOUT(MAX) = 15V, IQ = 2.6mA, ISD < 1µA, TSSOP Package LT3475 Dual Step-Down 1.5A, 2mV LED Driver VIN: 4V to 36V, IQ = 6mA, ISD < 1µA, 20-Lead TSSOPE Package LT3476 High Current 2MHz Quad 1.5A Output LED Driver VIN: 2.8V to 16V, VOUT(MAX) = 33.5V, IQ = 5.5mA, ISD < 1µA, 38-Lead 5mm × 7mm QFN Package LT3477 3A, 42V, 3MHz Step-Up Regulator with Dual Rail-to-Rail Current Sense VIN: 2.5V to 2.5V, VOUT(MAX) = 40V, IQ = 5mA, ISD < 1µA, QFN, 16-Pin TSSOPE Packages LT3478/LT3478-1 4.5A, 2.25MHz LED Driver with 3000:1 Ture Color PWM™ VIN: 2.8V to 36V, VOUT(MAX) = 40V, IQ = 6.1mA, ISD < 3µA, 16-Pin TSSOPE Package Dimming LT3479 3A, Full-Featured DC/DC Converter with Soft-Start and Inrush Current Protection VIN: 2.5V to 24V, VOUT(MAX) = 40V, IQ = 6.5mA, ISD < 1µA, DFN, TSSOP Packages 3496ff 20 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 l FAX: (408) 434-0507 l www.linear.com LT 0510 REV F • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2007