LT3476 datasheet(5/12 Pages) LINER

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LT3476

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PI FU CTIO S

VC1, VC4, VC3, VC2, (Pins 1, 12, 13, 38): Error Ampliﬁer

Compensation Pin. When PWM is low, VCpinﬂoatsexternal

compensation capacitor to save state for next cycle.

LED1, LED2, LED3, LED4, (Pins 2, 5, 8, 11): Non-

Inverting Input of Current Sense Error Ampliﬁer. Connect

directly to LED current sense resistor terminal. Switcher

will regulate this node to a voltage of 0.1 • VADJ below the

CAP node. Also connected to CAP node through external

sense resistor and to anode of LED string. Do not allow

this pin to ﬂoat independently of corresponding CAP input

pin. In applications where the LED current is low and the

PVIN changes widely, connect the output ﬁlter capacitor

to LEDn.

CAP1, CAP2, CAP3, CAP4, (Pins 3, 4, 9, 10): Inverting

input of current sense error ampliﬁer. Connect directly to

other terminal of LED current sense resistor. Also con-

nected to output ﬁlter capacitor and cathode of external

Schottky rectiﬁer. CAP greater than the overvoltage protect

threshold will inhibit switching.

RT (Pin 6): Oscillator Programming Pin. Place resistor

connected to GND to program oscillator frequency.

REF: (Pin 7): Reference Output Pin. Connect to VADJ pin

to get full-scale LED current. Connect to resistor dividers

to program VADJ pins to values lower than 1.05V. Bypass

to local GND with 0.1μF capacitor.

VADJ4, VADJ3, VADJ2, VADJ1, (Pins 14, 15, 36, 37): LED

Current Adjustment Pin. Sets voltage across external sense

resistor between CAPn and LEDn. Connect directly to

REF for full-scale threshold of 105mV, or use signal vales

between GND and REF to modulate LED current. VADJ pin

input range is 1.25V maximum.

PWM4, PWM3, PWM2, PWM1, (Pins 16, 17, 34, 35):

Signal low turns off the channel—disables the main

switch, reduces quiescent supply current to the channel,

and causes the VC pin for the channel to become high

impedance.

SHDN (Pin 18): Shutdown Pin. Higher than 1.5V turns

the device on.

NC (Pins 19, 20, 21, 30, 31, 32): Not Used. Connect to

GND (Pin 39) for better heat dissipation.

SW4,SW3,SW2,SW1,(Pins22,23,24,25,26,27,28,29):

SwitchPin.Connecttoexternalinductorandanodeofexternal

Schottky rectiﬁer. Minimize area of SW trace and use a

GND plane to reduce EMI. Adjacent pins of same name

are internally connected.

VIN (Pin 33): Input Supply Pin. Must be locally by-

passed.

GND (Pin 39): Signal and Power GND. Solder Exposed

Pad directly to ground plane. The Exposed Pad metal of

the package provides both electrical contract to ground

and good thermal contact to the printed circuit board.

It must be soldered to the circuit board for proper

operation.

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