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LT3597IUHG

60V Triple Step-Down LED Driver

Linear Technology 

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 pro-

grammed 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 Pro-

gramming 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

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