LT3476 datasheet(9/32 Pages) LINER

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LT3760

3760fc

block DiagraM

operaTion

TheoperationoftheLT3760isbestunderstoodbyreferring

to the typical application circuit on the front page and the

Block Diagram in Figure 1. The LT3760 drives 8 strings

of LEDs by using a constant switching frequency, current

mode boost controller to generate a single output voltage

VOUT for the top (anode) of all LED strings. LED string

current is generated and controlled by connection of the

bottom LED in each string (cathode) to a current source

contained in each corresponding LED pin. Each LED pin

contains an accurate current sink to ground, program-

mable between 20mA to 100mA using a single resistor

at the ISET pin. LED channels can be paralleled to achieve

higher LED currents. For applications requiring less than

8 strings of LEDs, channels can be paralleled or disabled

(connect LED pin to VOUT before startup). For optimum

efficiency, VOUT regulates to the lowest possible voltage

allowable to maintain regulated current in each LED string.

Any OPEN LED fault is indicated by the FAULT pin driven

low without effecting the operation of the connected LED

strings.

The Block Diagram in Figure 1 illustrates the key functions

of the LT3760. It can be seen that two external supplies,

VREF and INTVCC, are generated by the LT3760. The VREF

pinprovidesaprecision1.485Voutputforusewithexternal

resistors to program the CTRL, OVPSET and TSET input

pins. The INTVCC pin provides a regulated 7V output to

supply the gate driver for the boost controller GATE pin.

An accurate 1.476V threshold on the SHDN/UVLO pin

combinedwithaSHDN/UVLOpincurrenthysteresisallows

a programmable resistor divider from VIN to SHDN/UVLO

Figure 1. LT3760 Block Diagram

3760 BD

–

CHANNEL X

OVERVOLTAGE

AMP

LED AMP

1.1V

–

LED

LOGIC

–

INTVCC_UV

VIN_UV

VIN

SHDN_UV

SHDN/UVLO

PWM

VREF

CTRL

56R

600k

1.476V

1.485V

SLOPE

100mV

OVER

CURRENT

52mV

PEAK

CURRENT

HICCUP__MODE

PWM

7V(REGULATED)

UVLO(

+) = 3.8V, UVLO(−) = 3.4V

4.2V(

3.7V(

−)

–

REF

1.485V

VPTAT

–

GATE

SYNC

SENSE

VOUT

LEDx

6 TO 9, 20 TO 23

FAULT

SOFT

START

OSC

LED CURRENT

CONTROL

INTVCC

OVPSET

ISET

TSET

GND

PGND (10, 19, EXPOSED PAD (29))

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