Q: TLC5940 - Current Limitation by 1140759

We inherited a design from another company which uses the TLC5940 to drive a set of infrared LEDs at high-current. The VCC they are applying to the LEDs and the 5940 chip is 3.6V.

We are setting the current using a 332 ohm resistor on pin 27 (IREF), which should give us approximately 120mA of output current per channel. However, the datasheet states that operating the part at less than 3.6V limits our maximum current to 60mA. Could the part be damaged by this configuration?

If not, where does the 60mA limit come from? Is it possible to drive some of the channels at the full 120mA despite the lower VCC? If so, how many?

A: Re: TLC5940 - Current Limitation by 10449

Powering the TLC5940 with less than 3.6V and trying to sink 120mA will not damage the IC. The 60mA limitation exists becasuse 3.6V input voltage is not enough voltage to fully turn on the internal FETs to sink 120mA.   Although some TLC5940 IC may have outputs that can sink 120mA with Vcc=3.6V, this functionality is not specified to work and may not be repeatable from IC to IC.  Note that you can connect TLC5940 outputs in parallel.  With Vin=3.6V, you can change RIREF to set each output to 60mA and then connect two outputs in parallel to drive a single LED at 120mA.