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LT3744 - High Current Synchronous Step-Down LED Driver

LT3744 - High Current Synchronous Step-Down LED Driver
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LT3744 - High Current Synchronous Step-Down LED Driver - 1

LT3744 High Current Synchronous Step-Down LED Driver Features Ideal for Driving Up to 40A LEDs n Up to 3000:1 PWM Dimming n 20:1 Analog Dimming n ±3% Current Regulation Accuracy n ±3% Voltage Regulation Accuracy n Unique Inverting Buck-Boost Topology Allows Grounded Heat Sink to Be Used for RGB LEDs n 3.3V to 36V Input Voltage Range n Peak Current Mode with DC LED Current Sensing n Open and Shorted LED Protection and Fault Reporting n Floating LED Driver Allows Single Power Solution to Drive Multicolor LEDs or Single LED with Three Different Regulated Currents n Thermally Enhanced 5mm × 6mm QFN 36-Lead Package The LT®3744 is a fixed frequency synchronous step-down DC/DC controller designed to drive a LED load at up to 20A continuous or 40A pulsed. The peak current mode controller will maintain ±3% LED current regulation over a wide output voltage range, from VEE to VIN. By allowing VEE to float to negative voltages, several LEDs in series can be driven from a single Li-Ion battery with a simple, single step-down output stage. PWM dimming is achieved with the PWM pins. The regulated LED current is set with analog voltages at the CTRL pins. Regulated voltage and overvoltage protection are set with a voltage divider from the output to the FB pin. The switching frequency is programmable from 100kHz to 1MHz through an external resistor on the RT pin. Applications LED Driver for DLP Projectors Heads-Up Displays n High Power LED n n Additional features include an accurate external reference voltage, a control input for thermally derating regulation current, an accurate EN/UVLO pin, an open-drain output fault flag, OVLO, frequency synchronization, and thermal shutdown. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 7199560, 7321203, 8120335 and 8901904. Typical Application LED Driver for DLP Projectors EN/UVLO

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LT3744 - High Current Synchronous Step-Down LED Driver - 2

LT3744 Absolute Maximum Ratings UHE PACKAGE 36-LEAD (5mm × 6mm) PLASTIC QFN θJA = 34°C/W, θJC = 3°C/W EXPOSED PAD (PIN 37) IS VEE, MUST BE SOLDERED TO PCB

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LT3744 - High Current Synchronous Step-Down LED Driver - 3

LT3744 Order Information LEAD FREE FINISH PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE 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 nonstandard 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/ Electrical Characteristics The l denotes the specifications which apply over the...

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LT3744 - High Current Synchronous Step-Down LED Driver - 4

The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VEN/UVLO = 2V, SGND = VEE = 0V unless otherwise noted. PARAMETER NMOS FET Drivers Non-Overlap Time TG to BG Top Gate Driver Switch RON Gate Pull Up Gate Pull Down Bottom Gate Driver Switch RON Gate Pull Up Gate Pull Down PWM Out Drivers PWM_OUT Switch RON Gate Pull Up Gate Pull Down PWMX High To PWM_OUTX High Delay PWMX Low To PWM_OUTX Low Delay Oscillator Switching Frequency Range SYNC Input High SYNC Range Soft-Start Charge Current Fault Lower Fault...

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LT3744 - High Current Synchronous Step-Down LED Driver - 5

The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VEN/UVLO = 2V, SGND = VEE = 0V unless otherwise noted. PARAMETER Voltage Regulation Amplifier FB Pin Current gm Feedback Regulation Voltage LED Current Control Loop gm Amplifier Input Bias Current (LED_ISP and LED_ISN) Output Impedance Differential Gain C/10 Comparator Falling Threshold LED_ISN = 0V, Threshold = LED_ISP-LED_ISN, CTRL1 = CTRL2 = CTRL3 = 2V Rising Hysteresis LED_ISN = 0V, Threshold = LED_ISP-LED_ISN, CTRL1 = CTRL2 = CTRL3 = 2V Note 1:...

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LT3744 - High Current Synchronous Step-Down LED Driver - 6

LT3744 Typical Performance Characteristics EN/UVLO Threshold (Falling) EN/UVLO Hysteresis VREF UVLO VREF Current Limit Quiescent Current (Non-Switching) SOFT START PIN CURRENT (µA) VREF CURRENT LIMIT (mA)

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LT3744 - High Current Synchronous Step-Down LED Driver - 7

LT3744 Typical Performance Characteristics VBOOST - VSW UVLO (Falling Threshold) INTVCC UVLO (Falling Threshold) Frequency Foldback INTVCC Load Regulation NORMALIZED OSCILLATOR FREQUENCY INTVCC Current Limit Lower FAULT Threshold (Falling) Upper FAULT Threshold (Rising) Oscillator Frequency

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LT3744 - High Current Synchronous Step-Down LED Driver - 8

LT3744 Typical Performance Characteristics Regulated Sense Voltage ANALOG DIMMING LIMITED TO VCTRLX = 75mV (20:1) LED Current Regulation Accuracy 100 90 80 NUMBER OF UNITS Feedback Voltage NORMALIZED LOAD CURRENT (A/A) Average Current Regulation During Start-Up 140 RISING THRESHOLD Overcurrent Threshold LED Current Regulation Accuracy 300

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LT3744 - High Current Synchronous Step-Down LED Driver - 9

LT3744 Typical Performance Characteristics OVLO Threshold RISING THRESHOLD FALLING THRESHOLD RISING THRESHOLD FALLING THRESHOLD SYNC Threshold Bottom Gate Driver RDS(ON) Top Gate Driver RDS(ON) Non-Overlap PWM Signal Delay MINIMUM ON AND OFF TIME (nsec) 55 NON-OVERLAP TIME (nsec) DELAY (nsec) FALLING THRESHOLD RISING THRESHOLD MINIMUM ON-TIME

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LT3744 - High Current Synchronous Step-Down LED Driver - 10

LT3744 Typical Performance Characteristics LED Current Waveforms (0A to 20A) 2000:1 LED Current Waveforms (0A to 5A) 2000:1 Inverting Buck-Boost Regulator Voltage Regulation LED_ISP – LED_ISN Overvoltage Protection LED Current Waveforms (5000:1) 0A TO 20A Flicker-Free Performance LED Current Waveforms (0A to 10A) 1000:1 Inverting Regulator

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LT3744 - High Current Synchronous Step-Down LED Driver - 11

LT3744 Pin Functions EN/UVLO (Pin 1): The EN/UVLO pin acts as a precision enable and turns on the internal current bias core and subregulators with a rising threshold of 1.30V and a falling threshold of 1.235V. The pin has a 4.8μA pull-down current when below 1.235V. For normal operation, this pin requires a voltage bias. Full shutdown occurs at approximately 0.5V and low IQ operations is guaranteed below 0.3V. This pin is referenced to SGND. CTRL1, CTRL2, CTRL3 (Pin 2, 4, 5): The voltage at the CTRL pins set the regulated LED current. When PWM1 is high and PWM2 and PWM3 are low, CTRL1 is...

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