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TLC5927: LED power, IC power dissipation, and Heatsinking

Brian Mohlman
Prodigy 70 points
Part Number: TLC5927

Hello,

I have a design which I am using a pair of TLC5927 drivers. I am driving 32 Cree XLMLB LEDs, @ 40mA max each. My first question is how much heatsinking  will I need to provide via the PCB. I am using 2 0Z copper on the board and have an area underneath the drivers that I can connect the power pad to, to provide cooling. My second question is on some other parts the /OE line can be PWM'ed to provide dimming. My question is  can I PWM the /OE (ED2) to do the same on the TLC5927? Maybe get some heat dissipation benefit as well?

Thanks,

  • 0
    TI__Genius 14295 points
    Hi, Brian,

    Usually 2oz is enough and please make the underneath area as large as possible.

    OE pin can be used to provide dimming but since OE is used in special mode, please make sure there's no conflicts.

    BTW, you can also send different SDI to control the dimming.

    If you think this answers your question, please help to click "Resolve".

    Thanks.
    Regards,
    Kenneth
  • 0 in reply to Kenneth Du
    Prodigy 70 points

    Kenneth,

    Thanks for the information, I have included a picture of what I intend to do as far as heatsinking. the vias in the IC center pad are tied to ground. I am driving Cree XLMB cool white LEDs which have a forward voltage max of 3.5V @ 80mA and above. VDD is 3.3V, the LEDs are set 40mA and the forward voltage worst case is 3.5V I am planning on setting the LED voltage to 4 Volts to keep the differential down as much as  possible. Do you see any problems with this approach?

    Best Regards,

    Brian

  • 0 in reply to Brian Mohlman
    TI__Genius 14295 points

    Hi, Brian,

    The thermal performance should be OK.

    I have a little concern: as you can see from figure 1 of datasheet, to keep the Iout = 40mA, Vo=4-3.5=0.5V is a little critical.

    Vout>0.6V should be safe for your application. So you may need to increase Vled to 4.2V.

    If you think this answers your question, please help to click "Resolve".

    Thanks.

    Regards,

    Kenneth