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  • TI Thinks Resolved

TLC5917: Every time error on the same led

Part Number: TLC5917

Hi,

i have designed the led driver circuit using TLC5917 driving 4 ir leds, one per output from OUT0 to OUT3. The IC is powered by a 3.3V, and the Vled (stated in the ds) has the same supply rail.

I have an issue with the error detection on the least significative led; the error detection on the leds (open or short circuit) is a necessary feature for mine application.

What i have noticed is:

if i light on all the leds simultaneously and then i read the mask error, in absence of errors (short or open) i should read number 15 in the error register.

Since an error is found in the least significative led, the mask error is 14.

if i light on one led per time and then i read the mask error, i do not get any error. Why?

The design example on the ds shows a Vled rail different from the IC supply and the rail should have a voltage greater than the sum of the voltage drop on each led: 4 leds*2.7V=10.8V -> Vled at least = 11V

Why? 

My leds are not cascaded and does not share just one driver output, but each one have its own output.

Thanks

  • Hi, Michele,

    Let me take a look at this and reply you next Monday.

    Thanks.
    Regards,
    Kenneth
  • Hi, Michele,

    Since your LEDs are not cascaded, your Vled should be Vled=Vo+Vf.

    As you say, if lighting one LED per time, you can't read this error.

    Does this happen both for short and open?

    You can also check the voltage on OUT or the current to see whether there's difference between your two situations.

    Let me know your feedback.

    Thanks.
    Kenneth

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