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TLC5940 high current at all channels

Stefan Ludwig
Prodigy 10 points
Part Number: TLC5940

Dear TI-Team,

for my LED circuit I have 122 LEDs individually addressable by using 8 TLC5940 (RHBR). With an IRef sink current ist set to 100mA for each LED. 

Whats the right voltage to power LEDs and have as few power left to dissipate? Can I simply use 3V LED voltage or do I have to add some Volts? 

Is the driver suited to power 16 LEDs at such an current at 100% duty cycle at 100mA?

The logic and driver supply will be on a seperate 5V curcuit.

Thanks

KR
Stefan

  • 0
    TI__Genius 12915 points

    Hi Stefan,

    For VLED value, it need to be above forward voltage of LED Vf, plus saturation voltage on output pin as below image. Taking 100mA as example, to get a table output current, the voltage on output pins need to be above 1.5V. Leaving some margin for LED Vf variation, I think you could also connect VLED to your 5V supply.

    And yes all channels can support 100mA together when Vcc > 3.6V

  • 0 in reply to Hardy Wu
    Prodigy 10 points

    Hi Hardy,

    Thanks for your help.

    Right now Im a bit concerned about Power dissipation. Do you see any thermal issue when sinking remaining 1.5V and 100mA at 100% duty cycle? In the first attempt (at 5V VLED) the drivers have been destroyed.

    Kind Regards

    Stefan

  • 0 in reply to Stefan Ludwig
    TI__Genius 12915 points

    Hi Stefan,

    Do you know what part of the device is destroyed? The device is completely damaged, or just thermal shutdown and can be powered again?

    For thermal concerns, with the 16 channels 100mA setting, we could do a simple calculation by RθJA. The device temperature increases around 16 * 1.5V * 0.1A * 34.3 °C/W = 82°C. In normal room temp (25°C) and ventilation condition, I am afraid that the thermal condition is not good. Did you try using 4.5V supply?

  • 0 in reply to Hardy Wu
    Prodigy 10 points

    Hi Hardy, 

    I think its fatally damaged...

    I will try lowering the voltage.

    Might there be an issue for one LED driver where 6 channels are unused/not connected to any load, as these channels are set to sink current as well?

    KR Stefan

  • 0 in reply to Stefan Ludwig
    TI__Genius 12915 points

    Hi Stefan,

    The outputs are open drain structure. If there is no LED connection, they should also not work.