LT3597 60V Triple Step-Down LED Driver DESCRIPTION FEATURES Three 100mA Buck Regulators, Each Drives Up to 10 LEDs with Fast NPN Current Sources n Fast Current Sources for <1µs Pulse Widths (10,000:1 True Color PWM™ Dimming at 100Hz) n LEDs Disconnected in Shutdown n Adaptive V OUT for Increased Efficiency n 6V to 60V Input Voltage Range n ±2% LED Current Matching n External Resistor Sets LED Current for Each Channel n Internal Compensation and Soft-Start n Programmable Switching Frequency (200kHz to 1MHz) n Synchronizable to External Clock n Open LED Detection and Reporting n Shorted LED Pin Protection and Reporting n Programmable LED Thermal Derating n Programmable Temperature Protection n5mm × 8mm Thermally Enhanced QFN Package with a 0.6mm High Voltage Pin Spacing The LT®3597 is a 60V triple step-down LED driver capable of achieving 10,000:1 digital PWM dimming at 100Hz with fast NPN current sources driving up to 10 LEDs in each channel. LED dimming can also be achieved via analog control of the CTRL1-3 pin. n The step-down switching frequency is programmed between 200kHz and 1MHz. The frequency is also synchronizable to an external clock. The LT3597 provides maximum LED brightness while adhering to manufacturers’ specifications for thermal derating. The derate temperature is programmed by placing a negative temperature coefficient (NTC) resistor on the master control pin. The LT3597 adaptively controls VOUT in order to achieve optimal efficiency. Other features include: 2% LED current matching between channels, open LED reporting, shorted LED protection, programmable LED current, and programmable temperature protection. APPLICATIONS n n n n L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. LED Billboards and Signboards Mono, Multi, Full-Color LED Displays Large Screen Display LED Backlighting Automotive, Industrial, and Medical Displays TYPICAL APPLICATION Triple Step-Down RGB Single Pixel LED Driver, 100mA Current VIN 48V 10µF VIN 270k BOOST2 0.1µF 100µH EN/UVLO SW2 BOOST1 DA2 SW1 FB2 DA1 VOUT2 LED2 BOOST3 91k VOUT1 97k R 3.3µF 100µH 0.1µF 97k 9.1k G 3.3µF 9.1k VCC 5V 10,000:1 PWM Dimming at 100Hz VOUT2 FB1 LT3597 0.1µF 100µH VOUT1 LED1 BIAS 10µF 3.3µF 33.2k (1MHz) ILED 50mA/DIV 97k DA3 9.1k FB3 FAULT PWM1-3 CTRL1-3 SYNC RT 3 VOUT3 SW3 100k 3 PWM 2V/DIV ISET1 VOUT3 LED3 VREF ISET2 ISET3 GND 20k 20k 200ns/DIV 10k TSET CTRLM 3597 TA01a 20k B 82.5k 3597 TA01b VREF 49.9k 100k 3597f 1 LT3597 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) VIN BST2 SW2 DA2 TOP VIEW 51 50 48 46 44 VIN Input Voltage (VIN), EN/UVLO....................................60V BOOST1-3..................................................................85V BOOST Pin Above SW Pin......................................... 25V LED1-3, VOUT1-3.........................................................42V BIAS, FAULT...............................................................25V VREF, RT, ISET1-3 , TSET, CTRLM....................................3V FB1-3, CTRL1-3, PWM1-3, SYNC................................6V Operating Junction Temperature Range (Notes 2, 3).........................................–40°C to 125°C Maximum Junction Temperature........................... 125°C Storage Temperature Range....................–65°C to 150°C 43 DA3 BST1 2 41 SW3 SW1 4 39 BST3 DA1 6 37 BIAS FB1 7 53 GND EN/UVLO 9 35 FB3 34 FB2 TSET 11 33 CTRL1 VREF 12 32 CTRL2 CTRLM 13 31 CTRL3 ISET1 14 30 PWM1 ISET2 15 29 PWM2 ISET3 16 28 PWM3 RT 17 27 SYNC NC LED3 FAULT VOUT3 VOUT2 LED2 LED1 GND VOUT1 18 19 20 21 22 23 24 25 26 UHG PACKAGE VARIATION: UHG52(39) 52-LEAD (5mm × 8mm) PLASTIC QFN TJMAX = 125°C, θJA = 32°C/W EXPOSED PAD (PIN 53) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3597EUHG#PBF LT3597EUHG#TRPBF 3597 52-Lead (5mm × 8mm) Plastic QFN –40°C to 125°C LT3597IUHG#PBF LT3597IUHG#TRPBF 3597 52-Lead (5mm × 8mm) Plastic QFN –40°C to 125°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/ 3597f 2 LT3597 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 24V, BOOST = 29V, BIAS = 5V, EN/UVLO = 5V, PWM1-3 = 3.3V, CTRL1-3 = CTRLM = TSET = 2.0V, VOUT1-3 = 24V, SYNC = 0V, unless otherwise specified. (Note 2) PARAMETER CONDITIONS VIN Operating Voltage Quiescent Current from VIN MIN l EN/UVLO = 0.4V BIAS = 5V, Not Switching BIAS = 0V, Not Switching Minimum BIAS Voltage Quiescent Current from BIAS TYP 6 EN/UVLO = 0.4V BIAS = 5V, Not Switching BIAS = 0V, Not Switching, Current Out of Pin MAX UNITS 55 V 2.1 4 2 4 6 µA mA mA 3 3.1 V 2 60 2 3 150 µA mA µA EN Threshold (Falling) 0.4 0.7 UVLO Threshold (Falling) 1.47 1.51 1.53 V 4 10 5.1 6 nA µA 1.15 1.22 1.25 V 200 nA 90 78 95 85 EN/UVLO Pin Current (Hysteresis) EN/UVLO = 1.6V EN/UVLO = 1.4V FB1-3 Regulation Voltage FB1-3 Pin Bias Current FB = 6V Maximum Duty Cycle RT = 220k (200kHz) RT = 33.2k (1MHz) Switch Saturation Voltage ISW1-3 = 100mA V % % 265 mV Switch Current Limit 400 510 700 mA DA Pin Current to Stop OSC 225 280 350 mA 700 nA Switch Leakage VSW1-3 = 0V BST1-3 Pin Current ISW1-3 = 100mA Switching Frequency RT = 220k RT = 33.2k 2 170 900 200 1000 SYNC Input Low 230 1100 0.4 SYNC Input High 1.6 SYNC Frequency Range RT = 220k RT = 47k SYNC Pin Bias Current VSYNC = 3.3V Soft-Start Time (Note 4) VREF Voltage IVREF = 0µA 1.96 kHz kHz 200 nA 2.0 ms 2.04 200 RISET1-3 = 20k, VCTRL = VCTRLM = TSET = 1.5V TSET Voltage for LED Current Derating TSET Pin Leakage Current VTSET = 1.0V ILED1-3 LED Current RISET1-3 = 20k l 98 97 V 1000 2.5 l kHz kHz V 240 Maximum VREF Current ISET1-3 Pin Voltage mA V µA 1.0 V 540 mV 100 100 200 nA 102 103 mA mA 3597f 3 LT3597 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 24V, BOOST = 29V, BIAS = 5V, EN/UVLO = 5V, PWM1-3 = 3.3V, CTRL1-3 = CTRLM = TSET = 2.0V, VOUT1-3 = 24V, SYNC = 0V, unless otherwise specified. (Note 2) PARAMETER CONDITIONS LED String Current Matching RISET1-3 = 20k MIN l LED Pin Voltage Adaptive VOUT Loop Enabled LED1-3 Open Detection Threshold LED1-3 Short Protection Threshold (from GND) PWM1-3 = 3.3V 10 LED1-3 Short Protection Threshold (from VOUT1-3) VOUT1-3 = 6V 1 LED1-3 Pin Leakage Current VLED1-3 = 42V TYP MAX UNITS ±0.35 ±0.35 ±1.5 ±2 % % 1.1 V 0.28 V 1.25 PWM1-3 Input Low Voltage PWM1-3 Input High Voltage V 2 V 100 nA 0.4 V 1.6 V PWM1-3 Pin Bias Current 200 CTRL1-3 Voltage for Full LED Current CTRL1-3 Pin Bias Current 15 1.2 V CTRL1-3 = 6V CTRLM Voltage for Full LED Current 200 nA 200 nA 1.2 CTRLM Pin Bias Current CTRLM = 3V FAULT Output Voltage Low IFAULT = 200µA FAULT Pin Input leakage Current FAULT = 25V 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 LT3597E 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 LT3597I specifications are guaranteed over the full –40°C to 125°C operating junction temperature range. nA V 0.11 V 200 nA Note 3: For Maximum Operating Ambient Temperature, see Thermal Considerations in the Applications Information section. Note 4: Guaranteed by design. 3597f 4 LT3597 TYPICAL PERFORMANCE CHARACTERISTICS VIN Quiescent Current VBIAS = 5V 2.5 125°C 2.0 –40°C 25°C 1.5 1.0 VIN = 24V VIN = 55V 1.75 VBIAS = 25V 125°C 25°C 2.0 1.50 –40°C 1.5 1.0 0.5 0.5 0 Shutdown Current 2.00 2.5 VBIAS CURRENT (mA) VIN CURRENT (mA) VBIAS Quiescent Current 3.0 CURRENT (µA) 3.0 TA = 25°C, unless otherwise noted. 10 20 30 40 VIN VOLTAGE (V) 50 –0.5 60 IVIN IBIAS 5 0 10 15 VBIAS VOLTAGE (V) 20 0 –50 25 –25 0 25 50 75 TEMPERATURE (°C) 100 3597 G02 UVLO Threshold Voltage (Falling) EN/UVLO Pin Bias Current 1.7 VREF Voltage 2.04 5 125 3597 G03 6 1.8 VREF LOAD = 0µA 2.03 EN/UVLO = 1.4V 1.6 2.02 1.4 1.3 4 VREF VOLTAGE (V) 1.5 CURRENT (µA) UVLO VOLTAGE (V) 0.75 0.25 3597 G01 3 2 1.2 VIN = 55V VIN = 24V 2.01 2.00 VIN = 6V 1.99 1.98 1 1.1 –25 0 25 50 75 TEMPERATURE (°C) 100 0 –50 125 –25 75 0 25 50 TEMPERATURE (°C) 3597 G04 100 1.96 –50 125 Switching Frequency Current Limit RT = 33.2k CURRENT (mA) 0.6 0.4 RT = 220k 0.2 –25 0 25 50 75 TEMPERATURE (°C) SWITCH 400 DA 300 200 100 100 125 3597 G07 100 0 –50 –25 0 25 50 75 TEMPERATURE (°C) 125 Switch Voltage Drop 600 500 0.8 0 25 50 75 TEMPERATURE (°C) 3597 G06 600 1.0 –25 3597 G05 1.2 0 –50 1.97 EN/UVLO = 1.6V SWITCH VOLTAGE DROP (mV) 1.0 –50 FREQUENCY (MHz) 1.00 0.50 0 0 1.25 100 125 3597 G08 VBIAS = 5V 125°C 500 25°C 400 –40°C 300 200 100 0 0 50 100 150 200 SWITCH CURRENT (mA) 250 3597 G09 3597f 5 LT3597 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted. Soft-Start Boost Diode VF 60V Switching Waveforms 800 600 DIODE VF (mV) VEN/UVLO 5V/DIV –40°C 700 25°C 500 VSW 20V/DIV VSW 20V/DIV 125°C 400 200 VOUT 20V/DIV VOUT 20V/DIV 100 0 IL 100mA/DIV IL 100mA/DIV 300 2 0 4 6 8 DIODE CURRENT (mA) 3597 G11 400µs/DIV 10 3597 G12 400ns/DIV 3597 G10 Loop Regulation Voltage LED Current 0.50 LED CURRENT (mA) VFB 1.2 1.1 VLED (ADAPTIVE LOOP) 1.0 101 CH1 100 CH2 CH3 99 98 0.9 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 97 –50 125 –25 75 0 25 50 TEMPERATURE (°C) LED Current vs PWM Duty Cycle 125 10 100 LED CURRENT (mA) 120 1 0.1 0.01 0.001 0.1 1 DUTY CYCLE (%) 10 0 100 3597 G16 CH1 CH2 –0.25 –0.50 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 3597 G15 Adaptive Loop Operation ILED 100mA/DIV 80 VOUT 10V/DIV 60 VLED 10V/DIV 40 VSW 20V/DIV 20 0.01 CH3 LED Current vs CTRL 100 0.0001 0.001 100 0.25 3597 G14 3597 G13 LED CURRENT (mA) LED CURRENT MATCHING (%) 102 1.3 VOLTAGE (V) LED Current Matching 103 1.4 0 0 0.25 0.5 0.75 1 CTRL VOLTAGE (V) 1.25 1.5 400µs/DIV 3597 G18 3597 G17 3597f 6 LT3597 TYPICAL PERFORMANCE CHARACTERISTICS 20,000:1 PWM Dimming (100Hz) TA = 25°C, unless otherwise noted. 1,000:1 PWM Dimming (100Hz) PWM 2V/DIV PWM 2V/DIV ILED 50mA/DIV ILED 50mA/DIV 3597 G19 100ns/DIV Open LED Fault Shorted LEDs Fault VOUT 5V/DIV VOUT 5V/DIV VLED 2V/DIV VLED 5V/DIV ILED 100mA/DIV ILED 100mA/DIV VFAULT 5V/DIV VFAULT 5V/DIV 3597 G21 20ms/DIV 400 TSET LED Current Derating 0.8 120 25°C 200 40°C 150 100 LED CURRENT (mA) 250 0.6 0.5 0.4 0 0.6 0.2 0.4 0.8 FAULT PIN CURRENT (mA) 1 3597 G23 0.3 –50 80 60 40 20 50 0 VTSET = 0.675V 100 0.7 TSET VOLTAGE (V) FAULT PIN VOLTAGE (mV) 350 125°C 3597 G22 10ms/DIV TSET Voltage for Temperature Derating FAULT Pin Voltage Low 300 3597 G20 2µs/DIV –25 75 0 25 50 TEMPERATURE (°C) 100 125 3597 G24 0 25 45 65 85 105 TEMPERATURE (°C) 125 3597 G25 3597f 7 LT3597 PIN FUNCTIONS BOOST1, BOOST2, BOOST3 (Pins 2, 48, 39): Boost Capacitor Pin. This pin is used to provide a voltage that is higher than the input voltage when the switch is on to supply current to the switch driver. SW1, SW2, SW3 (Pins 4, 46, 41): Switch Pin. Connect the inductor, catch diode and boost capacitor to this pin. DA1, DA2, DA3 (Pins 6, 44, 43): Catch Diode Anode. This pin is used to provide frequency foldback in extreme situations. FB1, FB2, FB3 (Pins 7, 34, 35): Feedback Pin. This pin is regulated to the internal bandgap voltage. The maximum Buck output voltage can be set by connecting this pin to a resistor divider from VOUT1-3. EN/UVLO (Pin 9): Enable and Undervoltage Lockout Pin. Accurate 1.51V threshold. UVLO threshold can be programmed by using a resistor divider from VIN. If function is not required, pin can be tied to the VIN pin. TSET (Pin 11): Thermal Regulation Pin. Programs the LT3597 junction temperature at which LED current begins to derate. VREF (Pin 12): 2.0V Reference Output Pin. This pin can sources up to 200µA and can be used to program TSET and CTRLM. CTRLM (Pin 13): Master Control Pin. LED current derating vs temperature is achievable for all channels if the voltage on CTRLM has a negative temperature coefficient using an external NTC resistor in a voltage divider from VREF. ISET1, ISET2, ISET3 (Pins 14, 15, 16): LED Current Programming Pin. A resistor to ground programs full-scale LED current. RT (Pin 17): Switching Frequency Programming Pin. A resistor to ground programs the switching frequency between 200kHz and 1MHz. GND (Pin 18, Exposed Pad Pin 53): Ground Pin. This is the ground for both the IC and the switching converters. Exposed pad must be soldered to PCB ground. VOUT1, VOUT2, VOUT3 (Pins 19, 22, 23): Buck Output. This is the buck regulator output voltage sense into the IC. LED1, LED2, LED3 (Pins 20, 21, 24): Constant Current Sink Pin. These are 3 LED driver outputs, each containing an open collector, constant current sink. All outputs are matched within ±2% and are individually programmed up to 100mA using an external resistor at the ISET1-3 pin. Outputs are rated to allow a maximum VOUT1-3 of 42V. Connect the cathode of the LED string to LED1-3. Connect the anode of the LED string to VOUT1-3. FAULT (Pin 25): Fault Detection Pin. Open collector pin used to report open LED faults. FAULT must be externally pulled to a positive supply through a resistor. NC (Pin 26): No Connection Pin. Tie to ground. SYNC (Pin 27): External Clock Synchronization Pin. When an external clock drives this pin, the Buck regulators are synchronized to that frequency. Frequency programmed by the RT pin resistor must be at least 20% less than the SYNC pin clock frequency. PWM1, PWM2, PWM3 (Pins 30, 29, 28): PWM Dimming Control Pin. When driven to a logic high, the LED1-3 current sink is enabled. If PWM dimming is not desired, connect the pin to VREF. Channels can be individually disabled by tying PWM1-3 to ground. CTRL1, CTRL2, CTRL3 (Pins 33, 32, 31): Analog Dimming Control Pin. This pin is used to dim the LED current in an analog fashion. If the pin is tied to a voltage lower than 1.0V, it will linearly reduce the LED current. If feature is unused, connect the pin to VREF. BIAS (Pin 37): Supply Pin. This pin is the supply for an internal voltage regulator to internal analog and digital circuitry. BIAS must be locally bypassed with a 2.2µF capacitor. VIN (Pins 50, 51): Input Supply Pin. VIN must be locally bypassed with a 10µF capacitor to ground. Pins 50 and 51 are internally fused. 3597f 8 LT3597 BLOCK DIAGRAM LT3597 VIN EN/UVLO BIAS START-UP REFERENCE VREF BIAS + – BSTn SYNC S OSC RT Q R SWn SLOPE COMP + CHANNEL n n = 1-3 SOFT-START AND CLAMP VC 540mV PTAT TSET CTRLM CTRLn – + CONVERSION AND CONTROL – + – 1.22V + – 1.1V GND FBn VOUTn FAULT LED FAULT DETECTION LOGIC LEDn ISETn PWMn DAn PWM DIMMING LOGIC LED DRIVE CIRCUITRY GND, EXPOSED PAD 3597 BD Figure 1. Block Diagram 3597f 9 LT3597 OPERATION The LT3597 uses a constant frequency, internally compensated peak current mode control scheme. Operation is best understood by referring to the Block Diagram in Figure 1. Enable and undervoltage lockout (UVLO) are both controlled by a single pin. If the pin falls below 1.51V, an accurate comparator turns off the LED drivers and buck regulators. If the pin continues to fall to less than 0.4V, the part enters shutdown and consumes less than 2µA. The LT3597 contains three constant current sink LED drivers. Each of the three LED strings is powered from a dedicated adaptive buck converter in order to achieve maximum efficiency. The frequency of the buck regulators is programmed from 200kHz to 1MHz using an external resistor. The frequency can also be synchronized to an external clock using the SYNC pin. Internal buck compensation and soft-start requires few external components and permits simple board layout. A high-side switch current limit protects the internal switch during its on time, while a low side current limit prevents the switch from turning on in the case of excessive off phase current. Step-Down Adaptive Control Adaptive control of the output voltages achieves superior system efficiency. When a given channel’s PWM pin is low, the respective buck regulator output will go to a programmable high output voltage. In this case the buck will enter into a pulse-skipping mode since there is no load connected. This guarantees that the buck output voltage is high enough to immediately supply the LED current once the string is reactivated. As soon as PWM goes high, the output voltage of the buck will drop until there is 1V across the LED current sink. This scheme ensures the best efficiency for each LED channel. Since each LED string is independently driven from a separate buck channel, efficiency is optimized for all three strings even if the number of LEDs is mismatched between the channels. Another benefit of this regulation method is that the LT3597 starts up with 10,000:1 dimming even if the PWM1-3 pulse width is 1µs. Since VOUT starts up even if PWM1-3 is low, the part achieves high dimming ratios with narrow pulse widths within a couple of PWM1-3 clock cycles. LED Current Each LED string current can be individually programmed up to a maximum of 100mA with a 2% matching accuracy between the strings. An external resistor on the ISET1-3 pin programs the max current for that string. The CTRL1-3 pin can be used for analog dimming. Digital PWM can be programmed using the PWM1-3 pin. A dimming ratio of 10,000:1 can be achieved at a frequency of 100Hz. Fault Protection and Reporting The LT3597 protects against both open LED and shorted LED conditions. If the LED1-3 pin voltage exceeds 12V while the LED string is sinking current, or if the LED1-3 pin voltage is within 1.25V of VOUT1-3 pin voltage, the channel is disabled until the fault is removed. If the LED string opens, the LT3597 will limit the output to the voltage set by the FB resistor divider. The LT3597 reports a fault on the FAULT pin if any of the LED strings is open or shorted. LED faults are only reported if the respective string PWM signal is high. A fault is also reported if the internal die temperature reaches the TSET programmed derating limit. 3597f 10 LT3597 APPLICATIONS INFORMATION Inductor Selection Inductor values between 100µH and 470µH are recommended for most applications. It is important to choose an inductor that can handle the peak current without saturating. The inductor DCR (copper wire resistance) must also be low in order to minimize I2R power losses. Table 1 lists several recommended inductors. Typically 10µF capacitors are sufficient for the VIN and BIAS pins. The output capacitor for the buck regulators depends on the number of LEDs and switching frequency. Refer to Table 3 for the proper output capacitor selection. Table 3. Recommended Output Capacitor Values (VLED = 3.5V) SWITCHING FREQUENCY (kHz) # LEDS COUT (µF) 1000 1-3 3.3 >3 2.2 1-3 4.7 >3 3.3 1-3 15 >3 6.8 Table 1. Recommended Inductors 500 L (µH) DCR (Ω) CURRENT RATING (A) LPS6225 MSS1038 MSS1038 MSS1038 100 100 220 470 0.61 0.3 0.76 1.24 0.52 1.46 0.99 0.70 Coilcraft www.coilcraft.com CDRH105R CDRW105R CDRH105R CDR6D28MN 100 220 470 100 0.253 0.50 1.29 0.9 1.35 0.94 0.60 0.75 Sumida www.sumida.com DS1262C2 DS1262C2 DS1262C2 100 220 470 0.17 0.35 1.243 1.5 1.0 0.7 Toko www.toko.com SLF10145T SLF10145T 100 220 0.26 0.47 1.0 0.7 TDK www.tdk.com DR73 DR73 100 220 0.527 1.05 0.79 0.53 Coiltronics www.cooperet.com PART VENDOR Capacitor Selection Low ESR (equivalent series resistance) capacitors should be used at the outputs to minimize output ripple voltage. Use only X5R or X7R dielectrics, as these materials retain their capacitance over wider voltage and temperature ranges than other dielectrics. Table 2 lists some suggested manufacturers. Consult the manufacturers for detailed information on their entire selection of ceramic surface mount parts. 200 Diode Selection Schottky diodes, with their low forward voltage drop and fast switching speed, must be used for all LT3597 applications. Do not use P-N junction diodes. The diode’s average current rating must exceed the application’s average current. The diode’s maximum reverse voltage must exceed the application’s input voltage. Table 4 lists some recommended Schottky diodes. Table 4. Recommended Diodes PART MAX CURRENT MAX REVERSE (A) VOLTAGE (V) MANUFACTURER DFLS160 B160 1 1 60 60 Diodes, Inc. www.diodes.com CMMSH1-60 1 60 Central www.centralsemi.com ESIPB 1 100 Vishay www.vishay.com Table 2. Recommended Ceramic Capacitor Manufacturers Taiyo Yuden www.t-yuden.com AVX www.avxcorp.com Murata www.murata.com Kemet www.kemet.com TDK www.tdk.com 3597f 11 LT3597 APPLICATIONS INFORMATION Undervoltage Lockout (UVLO) Programming Maximum LED Current The EN/UVLO can be used to program the input UVLO threshold by connecting it to a resistor divider from the VIN pin as shown in Figure 2. Maximum LED current can be programmed by placing a resistor (RISET1-3) between the ISET1-3 pin and ground. RISET1-3 values between 20k and 100k can be chosen to set the maximum LED current between 100mA and 20mA respectively. LT3597 VIN R2 The LED current is programmed according to the following equation: EN/UVLO R1 1.51V + – 3597 F02 Figure 2. EN/UVLO Control Select R1 and R2 according to the following equation: ILED1-3 = 2 • (mA) Table 5. LED Current Programming RISET1-3 VALUE (kΩ) LED CURRENT (mA) 20 100 25 80 33.3 60 50 40 100 20 In UVLO an internal 5.1µA pull-down current source is connected to the pin for programmable UVLO hysteresis. The hysteresis can be set according to the following equation: 100 VUVLO(HYST) = 5.1µA • R2 80 LED CURRENT (mA) Once the EN/UVLO pin falls below 0.4V, the part enters into shutdown. RISET1-3 See Table 5 and Figure 3 for resistor values and corresponding programmed LED current. R2 VIN(UVLO) = 1.51V • 1+ R1 Care must be taken if too much hysteresis is programmed, the pin voltage might drop too far and cause the current source to saturate. 1V 60 40 20 0 0 25 50 RSET1-3 (kΩ) 75 100 3597 F03 Figure 3. RISET1-3 Value for LED Current 3597f 12 LT3597 APPLICATIONS INFORMATION LED Current Dimming Two different types of dimming control are available with the LT3597. The LED current can be dimmed using the CTRL1-3 pin or the PWM1-3 pin. For some applications, a variable DC voltage that adjusts the LED current is the preferred method for brightness control. In that case, the CTRL1-3 pin can be modulated to set the LED dimming (see Figure 4). As the CTRL1-3 pin voltage rises from 0V to 1.0V, the LED current increases from 0mA to the maximum programmed LED current in a linear fashion. As the CTRL1-3 pin continues to increase past 1.0V, the maximum programmed LED current is maintained. If this type of dimming control is not desired, the CTRL1-3 pin can be tied to VREF . 120 LED CURRENT (mA) 100 80 60 40 20 0 0 0.25 0.5 0.75 1 CTRL1-3 (V) 1.25 1.5 3597 F04 Figure 4. LED Current vs CTRL1-3 Voltage For True Color PWM dimming, the LT3597 provides up to 10,000:1 PWM dimming range at 100Hz. This is achieved by allowing the duty cycle of the PWM1-3 pin to be reduced from 100% to 0.01% for a PWM frequency of 100Hz (see Figure 5), hence a minimum on-time of 1µs and a maximum period of 100ms. PWM duty cycle dimming allows for constant LED color to be maintained over the entire dimming range. Using the TSET Pin for Thermal Protection The LT3597 contains a special programmable thermal regulation loop that limits the internal junction temperature. This thermal regulation feature provides important protection at high ambient temperatures, and allows a given application to be optimized for typical, not worstcase, ambient temperatures with the assurance that the LT3597 will automatically protect itself and the LED strings under worst-case conditions. As the ambient temperature increases, so does the internal junction temperature of the part. Once the programmed maximum junction temperature is reached, the LT3597 linearly reduces the LED current, as needed, to maintain this junction temperature. This can only be achieved when the ambient temperature stays below the maximum programmed junction temperature. If the ambient temperature continues to rise above the programmed maximum junction temperature, the LED current will reduce to less than 20% of the full current. A resistor divider from the VREF pin programs the maximum part junction temperature as shown in Figure 6. tPWM tON(PWM) LT3597 PWM1-3 LED1-3 CURRENT VREF MAX ILED R2 TSET 3597 F06 Figure 5. LED Current Using PWM Dimming R1 3597 F07 Figure 6. Programming the TSET Pin 3597f 13 LT3597 APPLICATIONS INFORMATION Table 6 shows commonly used values for R1 and R2. Choose the ratio of R1 and R2 for the desired junction temperature limit as described in Figure 7. Table 6. TSET Programmed Junction Temperature TJ (°C) R1 (kΩ) R2 (kΩ) 85 49.9 97.6 100 49.9 90.9 115 49.9 84.5 The TSET pin must be tied to VREF if the temperature protection feature is not desired. 0.8 TSET VOLTAGE (V) 0.7 0.6 0.5 LED Current Derating Using the CTRLM Pin Another feature of the LT3597 is its ability to program a derating curve for maximum LED current versus temperature. LED data sheets provide curves of maximum allowable LED current versus temperature to warn against exceeding this current limit and damaging the LED. The LT3597 allows the output LEDs to be programmed for maximum allowable current while still protecting the LEDs from excessive currents at high temperature. This is achieved by programming a voltage at the CTRLM pin with a negative temperature coefficient using a resistor divider with temperature dependent resistance (Figure 8). As ambient temperature increases, the CTRLM voltage will fall below the internal 1V voltage reference, causing LED currents to be controlled by the CTRLM pin voltage. The LED current curve breakpoint and slope versus temperature are defined by the choice of resistor ratios and use of temperature-dependent resistance in the divider for the CTRLM pin. 0.4 0.3 –50 –25 75 0 25 50 TEMPERATURE (°C) 100 125 3597 F07 Figure 7. TSET Voltage for Temperature Derating LT3597 VREF RY RY R2 R1 (OPTION A TO D) CTRLM RNTC RNTC A B RX C RX RNTC RNTC D 3597 F08 Figure 8. Programming the CTRLM Pin 3597f 14 LT3597 APPLICATIONS INFORMATION Table 7 shows a list of manufacturers/distributors of NTC resistors. There are several other manufacturers available and the chosen supplier should be contacted for more detailed information. If an NTC resistor is used to indicate LED temperature, it is effective only if the resistor is placed as closely as possible to the LED strings. LED derating curves shown by manufacturers are listed for ambient temperature. The NTC resistor should have the same ambient temperature as the LEDs. Since the temperature dependency of an NTC resistor can be nonlinear over a wide range of temperatures, it is important to obtain a resistor’s exact value over temperature from the manufacturer. Hand calculations of the CTRLM voltage can then be performed at each given temperature, resulting in the CTRLM versus temperature plotted curve. Iterations of resistor value calculations may be necessary to achieve the desired break point and slope of the LED current derating curve. From the CTRLM voltage, the LED current can be found using the curve shown in Figure 9. Table 7. NTC Resistor Manufacturers/Distributors Murata www.murata.com TDK Corporation www.tdk.com Digi-Key www.digikey.com Murata Electronics provides a selection of NTC resistors with complete data over a wide range of temperatures. In addition, a software tool is available which allows the user to select from different resistor networks and NTC resistor values, and then simulate the exact output voltage curve (CTRLM behavior) over temperature. Referred to as the “Murata Chip NTC Thermistor Output Voltage Simulator,” users can log onto www.murata.com and download the software followed by instructions for creating an output voltage VOUT (CTRLM) from a specified VCC supply (VREF). The CTRLM pin must be tied to VREF if the temperature derating function is not desired. Programming Switching Frequency The switching frequency of the LT3597 can be programmed between 200kHz and 1MHz by an external resistor connected between the RT pin and ground. Do not leave this pin open. See Table 8 and Figure 10 for resistor values and corresponding frequencies. Table 8. RT Resistor Selection SWITCHING FREQUENCY (MHz) RT VALUE (kΩ) 1.0 33.2 If calculating the CTRLM voltage at various temperatures gives a downward slope that is too strong, use alternative resistor networks (B, C, D in Figure 8). They use temperature independent resistance to reduce the effects off the NTC resistor over temperature. 100 1.0 SWITCHING FREQUENCY (MHz) 1.2 LED CURRENT (mA) 120 80 60 40 20 0 0 0.25 0.5 0.75 1 CTRLM (V) 1.25 1.5 3597 F09 Figure 9. LED Current vs CTRLM Voltage 0.5 80 0.2 220 0.8 0.6 0.4 0.2 0 25 50 75 100 125 150 175 200 225 RT (kΩ) 3597 F10 Figure 10. Programming Switching Frequency 3597f 15 LT3597 APPLICATIONS INFORMATION Selecting the optimum switching frequency depends on several factors. Inductor size is reduced with higher frequency, but efficiency drops slightly due to higher switching losses. Some applications require very low duty cycles to drive a small number of LEDs from a high supply. Low switching frequency allows a greater range of operational duty cycle and hence a lower number of LEDs can be driven. In each case, the switching frequency can be tailored to provide the optimum solution. When programming the switching frequency, the total power losses within the IC should be considered. Switching Frequency Synchronization The nominal operating frequency of the LT3597 is programmed using a resistor from the RT pin to ground over a 200kHz to 1MHz range. In addition, the internal oscillator can be synchronized to an external clock applied to the SYNC pin. The synchronizing clock signal input to the LT3597 must have a frequency between 240kHz and 1MHz, a duty cycle between 20% and 80%, a low state below 0.4V and a high state above 1.6V. Synchronization signals outside of these parameters will cause erratic switching behavior. For proper operation, an RT resistor is chosen to program a switching frequency 20% slower than the SYNC pulse frequency. Synchronization occurs at a fixed delay after the rising edge of SYNC. The SYNC pin must be grounded if the clock synchronization feature is not used. When the SYNC pin is grounded, the internal oscillator controls the switching frequency of the converter. Operating Frequency Trade-offs Selection of the operating frequency is a trade-off between efficiency, component size, output voltage and maximum input voltage. The advantage of high frequency operation is smaller component sizes and values. The disadvantages are lower efficiency and lower input voltage range for a desired output voltage. The highest acceptable switching frequency (fSW(MAX)) for a given application can be calculated as follows: fSW(MAX) = VD + VOUT tON(MIN) ( VD + VIN − VSW ) where VIN is the typical input voltage, VOUT is the output voltage, VD is the catch diode drop (0.5V) and VSW is the internal switch drop (0.5V at max load). This equation shows that slower switching is necessary to accommodate high VIN /VOUT ratios. The reason the input voltage range depends on the switching frequency is due to the finite minimum switch on and off times. The switch minimum on and off times are 200ns. Adaptive Loop Control The LT3597 uses an adaptive control mechanism to set the buck output voltage. This control scheme ensures maximum efficiency while not compromising minimum PWM pulse widths. When PWM1-3 is low, the output of the respective buck rises to a maximum value set by an external resistor divider to the respective FB pin. Once PWM1-3 goes high, the output voltage is adaptively reduced until the voltage across the LED current sink is 1V. Figure 11 shows how the maximum output voltage can be set by an external resistor divider. LT3597 VOUT1-3 VOUT1-3 R2 FB1-3 R1 3597 F11 Figure 11. Programming Maximum VOUT1-3 3597f 16 LT3597 APPLICATIONS INFORMATION The maximum output voltage must be set to exceed the maximum LED drop plus 1V by a margin greater than 10%. However, this margin must not exceed a voltage of 10V. This ensures proper adaptive loop control. The equations below are used to estimate the resistor divider ratio. The sum of the resistors should be less than 100k to avoid noise coupling to the FB pin. ) R2 VOUT(MAX) = 1.1 VLED(MAX) + 1.1V = 1.2V • 1+ R1 ( Fault Flag The FAULT pin is an open-collector output and needs an external resistor tied to a supply. If the LED1-3 pin voltage exceeds 12V or if the LED1-3 pin voltage is within 1.25V of VOUT1-3 pins while PWM1-3 is high, the FAULT pin will be pulled low. The FAULT pin will also be pulled low if the internal junction temperature exceeds the TSET programmed temperature limit. VMARGIN ≤ 10V There is a 3µs delay for FAULT flag generation when the PWM1-3 signal is enabled to avoid generating a spurious flag signal. The maximum current the FAULT can sink is typically 1mA. Minimum Input Voltage Thermal Considerations The minimum input voltage required to generate an output voltage is limited by the maximum duty cycle and the output voltage (VOUT) set by the FB resistor divider. The duty cycle is: VD + VOUT DC = VIN − VCESAT + VD The LT3597 provides three channels for LED strings with internal NPN devices serving as constant current sources. When LED strings are regulated, the lowest LED pin voltage is typically 1V. More power dissipation occurs in the LT3597 at higher programmed LED currents. For 100mA of LED current with a 100% PWM dimming ratio, at least 300mW is dissipated within the IC due to current sources. Thermal calculations must include the power dissipation in the current sources in addition to conventional switch DC loss, switch transient loss and input quiescent loss. VOUT(MAX) = VLED(MAX) +1.1V +VMARGIN where VD is the Schottky forward drop and VCESAT is the saturation voltage of the internal switch. The minimum input voltage is: VD + VOUT(MAX) VIN(MIN) = + VCESAT − VD DCMAX where VOUT(MAX) is calculated from the equation in the Adaptive Loop Control section, and DCMAX is the minimum rating of the maximum duty cycle. In addition, the die temperature of the LT3597 must be lower than the maximum rating of 125°C. This is generally not a concern unless the ambient temperature is above 100°C. Care should be taken in the board layout to ensure good heat sinking of the LT3597. The maximum load current should be derated as the ambient temperature approaches 125°C. The die temperature rise above ambient is calculated by multiplying the LT3597 power dissipation by the thermal resistance from junction to ambient. Power dissipation within the LT3597 is estimated by calculating the total power loss from an efficiency measurement and subtracting the losses of the catch diode and the inductor. Thermal resistance depends on the layout of the circuit board, but 32°C/W is typical for the 5mm × 8mm QFN package. 3597f 17 LT3597 APPLICATIONS INFORMATION Board Layout As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To prevent electromagnetic interference (EMI) problems, proper layout of high frequency switching paths is essential. Minimize the length and area of all traces connected to the switching node pin (SW). Always use a ground plane under the switching regulator to minimize interplane coupling. Good grounding is essential in LED fault detection. Proper grounding is also essential for the external resistors and resistor dividers that set critical operation parameters. Both the LT3597 exposed pad and pin 18 are ground. Resistors connected between ground and the CTRL1-3, CTRLM, FB1-3, TSET, ISET1-3, RT and EN/UVLO pins are best tied to pin 18 and not the ground plane. 3597f 18 LT3597 TYPICAL APPLICATIONS 48V 1MHz Triple Step-Down 100mA RGB LED Driver VIN 48V 10µF VIN 270k BOOST2 0.1µF 100µH EN/UVLO SW2 BOOST1 DA2 SW1 FB2 DA1 VOUT2 LED2 BOOST3 91k 100µH 97k R 2.2µF 0.1µF 9.1k VCC 5V 97k 4.7k B 3.3µF FB1 LT3597 0.1µF 100µH VOUT1 LED1 BIAS 10µF 2.2µF 33.2k (1MHz) 3.83k FB3 FAULT PWM1-3 CTRL1-3 SYNC RT 3 97k DA3 100k 3 VOUT3 SW3 ISET1 VOUT3 LED3 VREF ISET2 ISET3 GND 20k 20k 10k TSET CTRLM 3597 TA02 20k 82.5k G VREF 49.9k 100k Efficiency 90 80 70 EFFICIENCY (%) VOUT1 VOUT2 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 LED CURRENT PER CHANNEL (mA) 3597 TA02b 3597f 19 LT3597 TYPICAL APPLICATIONS 48V 1MHz Triple Step-Down 10W 100mA White LED Driver (3.6V LEDs) VIN 48V 10µF VIN 270k BOOST2 0.1µF 100µH EN/UVLO SW2 BOOST1 DA2 SW1 FB2 DA1 VOUT2 LED2 BOOST3 91k VOUT1 97k 2.2µF 100µH 0.1µF 97k 3.24k 2.2µF 3.24k VCC 5V VOUT2 FB1 LT3597 VOUT1 LED1 BIAS 10µF 2.2µF 33.2k ISET1 VOUT3 LED3 VREF ISET2 ISET3 20k 10k TSET GND CTRLM 3597 TA03 20k 97k 3.24k FB3 FAULT PWM1-3 CTRL1-3 SYNC RT 3 VOUT3 DA3 100k 3 0.1µF 100µH SW3 20k 82.5k VREF 49.9k 100k Efficiency 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 LED CURRENT PER CHANNEL (mA) 3597 TA03b 3597f 20 LT3597 TYPICAL APPLICATIONS 24V 200kHz Triple Step-Down 100mA RGB LED Driver VIN 24V VIN 10µF BOOST2 EN/UVLO SW2 BOOST1 DA2 SW1 FB2 DA1 VOUT2 LED2 BOOST3 0.22µF 470µH VOUT2 15µF VOUT1 470µH 97k 9.1k G 15µF 9.1k FB1 LT3597 VOUT1 LED1 BIAS 10µF 3 VOUT3 15µF 97k 9.1k FB3 220k 470µH DA3 FAULT PWM1-3 CTRL1-3 SYNC RT 3 0.22µF SW3 100k ISET1 VOUT3 LED3 VREF ISET2 ISET3 GND B VREF TSET CTRLM 3597 TA04 20k 20k 20k Efficiency 90 80 70 EFFICIENCY (%) R 0.22µF 97k 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 LED CURRENT PER CHANNEL (mA) 3597 TA04b 3597f 21 LT3597 TYPICAL APPLICATIONS 48V 1MHz Triple Step-Down 20mA RGB LED Driver VIN 48V 10µF VIN 270k BOOST2 0.1µF 100µH EN/UVLO SW2 BOOST1 DA2 SW1 FB2 DA1 VOUT2 LED2 BOOST3 91k VOUT1 R 2.2µF 100µH 97k 0.1µF 97k 4.7k B 3.3µF 9.1k VCC 5V VOUT2 FB1 LT3597 0.1µF 100µH VOUT1 LED1 BIAS 10µF 2.2µF 33.2k 3.83k FB3 FAULT PWM1-3 CTRL1-3 SYNC RT 3 97k DA3 100k 3 VOUT3 SW3 ISET1 VOUT3 LED3 VREF ISET2 ISET3 GND TSET CTRLM 3597 TA05 100k 100k 100k 10k 82.5k G VREF 49.9k 100k 3597f 22 LT3597 PACKAGE DESCRIPTION UHG Package Variation: UHG52 (39) 52-Lead Plastic QFN (5mm × 8mm) (Reference LTC DWG # 05-08-1846 Rev B) 43 41 39 6.40 REF 35 34 33 32 31 30 29 28 37 27 0.70 ± 0.05 44 26 25 24 46 5.50 ± 0.05 4.10 ± 0.05 23 48 22 3.20 REF 21 2.90 ±0.05 50 20 5.90 ±0.05 51 19 18 PACKAGE OUTLINE 2 4 6 0.80 BSC 7 9 11 12 13 14 15 16 0.40 BSC 17 0.20 ± 0.05 7.10 ± 0.05 8.50 ± 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 51 50 48 46 44 R = 0.10 TYP 0.75 ± 0.05 5.00 ± 0.10 0.00 – 0.05 46 48 PIN 1 NOTCH R = 0.30 TYP OR 0.35 × 45° CHAMFER 50 51 0.40 ±0.10 PIN 1 TOP MARK (SEE NOTE 6) 43 43 41 41 39 39 7 37 37 9 35 35 6.40 REF 2 44 R = 0.10 TYP 2 4 4 6 6 7 9 34 34 11 33 33 12 32 32 12 13 31 31 14 30 30 13 14 15 29 29 16 28 17 27 28 27 8.00 ± 0.10 11 0.20 ± 0.05 0.80 BSC 0.60 TYP 0.40 BSC 15 5.90 ±0.10 2.90 ±0.10 16 17 0.70 TYP 0.200 REF 0.75 ± 0.05 26 25 24 23 22 21 20 19 18 (UHG39) QFN 0410 REV B 3.20 REF BOTTOM VIEW—EXPOSED PAD 18 19 20 21 22 23 24 25 26 0.00 – 0.05 NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 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 0.20mm 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 3597f 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. 23 LT3597 TYPICAL APPLICATION Triple Step-Down RGB Single Pixel LED Driver, 100mA Current VIN 48V 10µF VIN 270k BOOST2 0.1µF 100µH EN/UVLO SW2 BOOST1 DA2 SW1 FB2 DA1 VOUT2 LED2 BOOST3 91k VOUT1 0.1µF PWM 2V/DIV 97k G 9.1k 3.3µF 9.1k VCC 5V 10µF VOUT2 3.3µF 100µH 97k R 10,000:1 Dimming at 100Hz FB1 LT3597 0.1µF 100µH VOUT1 LED1 BIAS 10µF VOUT3 SW3 3.3µF 200ns/DIV 97k 3597 TA06b DA3 100k 9.1k FB3 FAULT PWM1:3 CTRL1:3 SYNC RT 33.2k ILED 50mA/DIV ISET1 VOUT3 LED3 VREF ISET2 ISET3 GND TSET CTRLM 3597 TA06 20k 20k 10k 20k 82.5k B VREF 49.9k 100k RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT3476 Quad Output 1.5A, 2MHz High Current LED Driver with 1000:1 Dimming VIN: 2.8V to 16V, VOUT(MAX) = 36V, True Color PWM Dimming = 1000:1, ISD < 10µA, 5mm × 7mm QFN-10 Package LT3492 60V, 2.1MHz 3-Channel (ILED = 1A) Full Featured LED Driver VIN: 3V to 30V (40VMAX), VOUT(MAX) = 60V, True Color PWM Dimming = 3000:1, ISD < 1µA, 4mm × 5mm QFN-28 Package LT3496 45V, 2.1MHz 3-Channel (ILED = 1A) Full Featured LED Driver VIN: 3V to 30V (40VMAX), VOUT(MAX) = 45V, True Color PWM Dimming = 3000:1, ISD < 1µA, 4mm × 3mm QFN-28 Package LT3590 48V, 850kHz 50mA Buck Mode LED Driver VIN: 4.5V to 55V, True Color PWM Dimming = 200:1, ISD < 15µA, 2mm × 2mm DFN-6 and SC70 Packages LT3595 45V, 2.5MHz 16-Channel Full Featured LED Driver VIN: 4.5V to 55V, VOUT(MAX) = 45V True Color PWM Dimming = 5000:1, ISD < 1µA, 5mm × 9mm QFN-56 Package LT3596 60V, 1MHz 3-Channel Full Featured LED Driver VIN: 6V to 60V, VOUT(MAX) = 40V, True Color PWM Dimming = 10,000:1, ISD ≤ 2µA, 5mm × 8mm QFN-52 Package LT3598 44V, 1.5A, 2.5MHz Boost 6-Channel LED Driver VIN: 3V to 30V (40VMAX), VOUT(MAX) = 44V, True Color PWM Dimming = 1000:1, ISD < 1µA, 4mm × 4mm QFN-24 Package LT3599 2A Boost Converter with Internal 4-String 150mA LED VIN: 3V to 30V, VOUT(MAX) = 44V, True Color PWM Dimming = 1000:1, ISD < 1µA, 5mm × 5mm QFN-32 and TSSOP-28 Packages Ballaster LT3754 16-Channel x 50mA LED Driver with 60V Boost Controller and PWM Dimming VIN: 6V to 40V, VOUT(MAX) = 60V, True Color PWM Dimming = 3000:1, ISD < 2µA, 5mm × 5mm QFN-52 Package LT3760 8-Channel x 100mA LED Driver with 60V Boost Controller and PWM Dimming VIN: 6V to 40V, VOUT(MAX) = 60V, True Color PWM Dimming = 3000:1, ISD < 2µA, TSSOP-28 Package 3597f 24 Linear Technology Corporation LT 0311 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2011