Integrated 8-Channel LED Drivers with

Switch-Mode Boost and SEPIC Controller

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11

Detailed Description

The MAX16807/MAX16808 LED drivers include an

internal switch-mode controller that can be used as

boost or buck-boost (SEPIC) converters to generate the

voltage necessary to drive the multiple strings of LEDs.

These devices incorporate an integrated low-side dri-

ver, a programmable oscillator (20kHz to 1MHz), an

error amplifier, a low-voltage (300mV) current sense for

higher efficiency, and a 5V reference to power up

external circuitry (see Figures 1a, 1b, and 1c).

The MAX16807/MAX16808 LED drivers include a 4-wire

serial interface and a current-mode PWM controller to

generate the necessary voltage for driving eight open-

drain, constant-current-sinking output ports. The drivers

use current-sensing feedback circuitry (not simple cur-

rent mirrors) to ensure very small current variations over

the full allowed range of output voltage (see the

Typical

Operating Characteristics). The 4-wire serial interface

comprises an 8-bit shift register and an 8-bit transpar-

ent latch. The shift register is written through a clock

input, CLK, and a data input, DIN, and the data propa-

gates to a data output, DOUT. The data output allows

multiple drivers to be cascaded and operated together.

The contents of the 8-bit shift register are loaded into

the transparent latch through a latch-enable input, LE.

The latch is transparent to the shift register outputs

when high and latches the current state on the falling

edge of LE. Each driver output is an open-drain, con-

stant-current sink that should be connected to the cath-

Pin Description

PIN

NAME

FUNCTION

1, 13, 28

N.C.

No Connection. Not internally connected. Leave unconnected.

2

AGND

Analog Ground

3

OUT

MOSFET Driver Output OUT. Connects to the gate of the external n-channel MOSFET.

of a 0.1µF and a higher value ceramic capacitor.

5

REF

5V Reference Output. Bypass REF to AGND with a 0.1µF ceramic capacitor.

6–9

OUT4–OUT7

LED Driver Outputs. OUT4–OUT7 are open-drain, constant-current-sinking outputs rated for 36V.

10

OE

Active-Low Output Enable Input. Drive OE low to PGND to enable the OUT0–OUT7. Drive OE high to

disable OUT0–OUT7.

11

DOUT

Serial-Data Output. Data is clocked out of the 8-bit internal shift register to DOUT on CLK’s rising

edge.

12

SET

14

V+

LED Driver Positive Supply Voltage. Bypass V+ to PGND with a 0.1µF ceramic capacitor.

15, 16

PGND

Power Ground

17

DIN

Serial-Data Input

18

CLK

Serial-Clock Input

19

LE

Latch-Enable Input. Data is loaded transparently from the internal shift register(s) to the output

latch(es) while LE is high. Data is latched into the output latch(es) on LE’s falling edge, and retained

while LE is low.

20–23

OUT0–OUT3

LED Driver Outputs. OUT0–OUT3 are open-drain, constant-current-sinking outputs rated for 36V.

24

COMP

Error-Amplifier Output

25

FB

Error-Amplifier Inverting Input

26

CS

PWM Controller Current-Sense Input

27

RTCT

—EP

Exposed Paddle. Connect to the ground plane for improved power dissipation. Do not use as the

only ground connection for the part.