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TLC59108: TLC59108 thermal calculation

Masayuki Seike
Prodigy 20 points
Part Number: TLC59108

I have a question about the thermal calculation of TLC59108.

Connect Vf = 1.5V LED to all output terminals.
LEDanode = 5V
REXT = 187ohm
Turn on all LEDs.

Please tell me how to calculate the power loss when Duty = 100% under these conditions.

and

Please tell me how to calculate the power loss when Duty = 50% under these conditions.

  • +1
    TI__Genius 12915 points

    Hi Masayuki,

    I do not recommend to use VLED as 5V. With REXT = 187ohm, IOUT is set around 100mA. The voltage dropped on output pins is 5V - 1.5V = 3.5V. So that total power dissipation on output pin is 100mA * 3.5V * 8 = 2.8W. The power consumption by the device own is around 5V * 28mA = 0.14W.

    For TSSOP package (RθJA = 98.9C/W), the device temperature increment is around 98.9 * 2.94W = 291C, which is much above the thermal shutdown threshold and cannot be used.
    For VQFN (RθJA = 39.1C/W), the device temperature increment is around 39.1 * 2.8W = 115C, which is still cannot be acceptable.

    Usually we recommend to leave 1V on output channels, as setting VLED = 2.5V in your case. While setting duty to 50%, you could treat the power consumption as half of duty = 100%

  • 0 in reply to Hardy Wu
    Prodigy 20 points

    Hello Hardy Wu.

    I understand.
    thank you.