LT3760 Просмотр технического описания (PDF) - Linear Technology

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производитель

LT3760

8-Channel × 100mA LED Driver

Linear Technology 

LT3760

Block Diagram

SHDN/UVLO

15

+

600k 1.476V –

14

VIN

13

INTVCC

7V(REGULATED) UVLO(+) = 3.8V, UVLO(−) = 3.4V

R

S

VC

SLOPE

OSC

REF

1.485V

PWM

27

3 VREF

CTRL

1

INTVCC_UV

VIN_UV

SHDN_UV

4.2V(+)

3.7V(−)

1.485V

EN

EN

6V

1V

+++–

LED CURRENT

CONTROL

CHANNEL X

LED

LOGIC

–

+

1.1V

LED AMP

52mV

PEAK

CURRENT

SOFT

START

SS

OVERVOLTAGE

AMP

Q

GATE

12

EN

SYNC 17

RT

25

100mV

OVER

CURRENT

HICCUP__MODE

SENSE

11

VOUT 18

LEDx

6 TO 9, 20 TO 23

FAULT

EN

16

PWM

56R

VPTAT

TSET

2

ISET

4

GND

24

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

VC

26

Figure 1. LT3760 Block Diagram

R

OVPSET

28

3760 BD

Operation

The operation of the LT3760 is best understood by referring

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

pin provides a precision 1.485V output for use with external

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

combined with a SHDN/UVLO pin current hysteresis allows

a programmable resistor divider from VIN to SHDN/UVLO

3760fc

9

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