Applications Information

LED Output Current

LED current for outputs OUT0–OUT15. The minimum

Ω, which sets the output

is 5k

Ω. The reference value, 360Ω, sets the output cur-

rents to 50mA. To set a different output current, use the

formula:

Computing Power Dissipation

MAX6971 is determined by the following equation:

where:

V+ = supply voltage

drive current into N outputs

DUTY = PWM duty cycle applied to OE

N = number of MAX6971 outputs driving LEDs at the

same time (maximum is 16)

LED(s)

Dissipation example:

5.25V

+82°C/W from the Absolute Maximum Ratings), the

Overtemperature Cutoff

The MAX6971 contains an internal temperature sensor

that turns off all outputs when the die temperature

exceeds approximately +165°C. The outputs are

enabled again when the die temperature drops below

approximately +140°C. Register contents are not

affected, so when a driver is overdissipating, the exter-

nal symptom is the load LEDs cycling between on and

off as the driver repeatedly overheats and cools, alter-

nately turning the LEDs off and then back on again.

Power-Supply Considerations

The MAX6971 operates with a chip supply V+, and one

or more LED supplies. Bypass each supply to GND

with a 0.1µF capacitor as close to the MAX6971 as pos-

sible. This is normally adequate for static LED driving.

For multiplex or PWM applications, it is necessary to

add an additional bulk electrolytic capacitor of 4.7µF or

more to each supply for every 4 to 16 MAX6971s. The

necessary capacitance depends on the LED load cur-

rent, PWM switching frequency, and serial-interface

speed. Inadequate V+ decoupling can cause timing

problems, and very noisy LED supplies can affect LED

current regulation.

Chip Information

PROCESS: BiCMOS

16-Port, 36V Constant-Current LED Driver

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