LT3486 datasheet(6/20 Pages) LINER

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LT3486

3486f

PI FU CTIO S

SW1, SW2 (Pins 1, 16): The SW Pins are the Collectors

of the Internal Power Transistors. Connect the inductors

and Schottky diodes to these pins. Minimize trace area

at these pins to minimize EMI.

VIN (Pin 2): Input Supply Pin. Must be locally bypassed

with an X5R or X7R type ceramic capacitor.

OVP1, OVP2 (Pins 3, 14): Output Overvoltage Protection

Pins. Connect these pins to the output capacitors. The

on-chip voltage detectors monitor the voltages at these

pins and limit it to 36V (typ) by turning off the respective

switcher and pulling its VC pin low.

RT (Pin 4): Timing Resistor to Program the Switching

Frequency. The switching frequency can be programmed

from 200kHz to 2MHz.

VC1, VC2 (Pins 5, 12): The VC Pins are the Outputs of the

Internal Error Ampliﬁer. The voltages at these pins control

the peak switch currents. Connect a resistor and capacitor

compensation network from these pin to ground.

FB1, FB2 (Pins 6, 11): The LT3486 regulates the voltage

at each feedback pin to 200mV. Connect the cathode of

the lowest LED in the string and the feedback resistor

(RFB) to the respective feedback pin. The LED current in

each string can be programmed by:

ILED ≅ 200mV/RFB, when VCTRL > 1.8V

ILED ≅ VCTRL/(5RFB), when VCTRL < 1V

CTRL1, CTRL2 (Pins 7, 10): The CTRL pins are used to

provide dimming and shutdown control for the individual

switching converters. Connecting these to ground shuts

down the respective converter. As the voltages on these

pins is ramped from 0V to 1.8V, the LED current in each

converter ramps from 0 to ILED = (200mV/RFB). Any volt-

age above 1.8V does not affect the LED current.

PWM1, PWM2 (Pins 8, 9): The PWM control pins can

be used to extend the dimming range for the individual

switching converter. The LED current in each string can

be controlled down to µA levels by feeding a PWM signal

to these pins. When the PWM pin voltage is taken below

0.4V, the respective converter is turned off and its VC pin

is disconnected from the internal circuitry. Taking it higher

than 0.9V resumes normal operation. Connect these pins

to 0.9V supply or higher, if not in use.

SHDN (Pin 13): Shutdown Pin for the Device. Connect it

to 1.6V or higher to enable device; 0.4V or less to disable

device.

REF (Pin 15): The internal bandgap reference (1.25V) is

available at this pin. Bypass with a 0.1µF X5R or X7R ce-

ramic capacitor. Draw no more than 50µA from this pin.

Exposed Pad (Pin 17): The exposed pad of the package

provides an electrical contact to ground and good thermal

connection to the printed circuit board (PCB). Solder the

exposed pad to the PCB system ground.

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