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TLC5940 LED power supply voltage

Madhu Vatte
Intellectual 835 points
Other Parts Discussed in Thread: TLC5940

Hello,

I was looking at TLC5940 for 4 strings of LEDs with 6 LEDs in each string.  If the forward voltage is 3.3V, total would be 19.8V for each string which is greater than the LED power supply voltage which is up to 17V according to the datasheet.  Can you please explain why there is a limit of 17V, is it the max. power the chip can handle (17V and max. current of 120mA which is around 2W) which is the dissipation rating in page 5?

http://www.ti.com/lit/ds/symlink/tlc5940-ep.pdf

Thanks,

Madhu

  • 0
    Prodigy 5 points

    Madhu, the Vcc rating is 5V, and the output current sinks are rated at 17V.
    With the LEDS all in series the TLC current sink will only see the difference between Vsupply(led) and Vled(string).

    So a 19.8V LED string would perhaps need a 21V source.
    So the TLC driver will see 21 - 19.8 = 1.2V