Datasheet

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Detailed Description

The MAX6979 LED driver comprises a 4-wire serial

interface driving eight constant-current sinking open-

drain output ports. The outputs drive LEDs in either sta-

tic or multiplex applications (Figure 1). The constant-

current outputs are guaranteed for current accuracy

not only with chip-supply voltage variations (5V ±10%

and 3V to 5.5V), but also over a realistic range of driver

output voltage drop (0.5V to 2.5V). The drivers use cur-

rent-sensing feedback circuitry (not simple current mir-

rors) to ensure very small current variations over the full

allowed range of output voltage (see the

Typical

Operating Characteristics

MAX6979

16-Port, 5.5V Constant-Current LED Driver with

LED Fault Detection and Watchdog

6 _______________________________________________________________________________________

Pin Description

PIN NAME FUNCTION

1 GND Ground

2 DIN Serial-Data Input. Data is loaded into the internal 16-bit shift register on CLK’s rising edge.

3 CLK Serial-Clock Input. Data is loaded into the internal 16-bit shift register on CLK’s rising edge.

4LE

Load-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.

5–20

OUT0–

OUT15

LED Driver Outputs. OUT0 to OUT15 are open-drain, constant-current-sinking outputs rated to 5.5V.

21 OE

Output Enable Input. High forces outputs OUT0 to OUT15 high impedance without altering the contents of

the output latches. Low enables outputs OUT0 to OUT15 to follow the state of the output latches.

22 DOUT Serial-Data Output. Data is clocked out of the 16-bit internal shift register to DOUT on CLK’s rising edge.

23 SET LED Current Setting. Connect SET to GND through a resistor (R

SET

) to set the maximum LED current.

24 V+ Positive Supply Voltage. Bypass V+ to GND with a 0.1µF ceramic capacitor.

SERIAL-TO-PARALLEL SHIFT REGISTER

LATCHES

OUT0

OUT1

OUT2

DOUT

DIN

CLK

OUT15

CONSTANT-CURRENT SINKS

OUT13

OUT14

POWER-ON

RESET

V+

CURRENT

REFERENCE

V+

GND

D0 D15

SET

MAX6979

FAULT DETECTION

WATCH-

DOG

Figure 1. MAX6979 Block Diagram