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TPA3255: Attaching Heatsink to the Thermal Pad

Imad Shaham
Prodigy 30 points
Part Number: TPA3255

Hi,

During my design of a TPA3255 amplifier, I ran into a design complication. The four 1 uF 100 V X7R MLCC capacitors connected to PVDD pins of the chip extend to a height of 1.6 mm. The chip itself extends to a maximum height of 1.2 mm according to the datasheet. Therefore considering the capacitors have greater height, how is the heatsink meant to make direct contact with the chip?

Furthermore, wouldn't the heatsink making contact with both pins of all the capacitors cause them to short circuit?

Best Regards and Thanks,

I. Shaham

  • +1
    TI__Mastermind 39830 points

    Hi I. Shaham

        You are correct, we'll need to avoid the heatsink contact other devices.

        Usually we'll suggest customer to build a contact pad on the heatsink in the center, not a entirely flat surface of the heatsink. Like below picture shows an example. Of course the 1.6mm is not enough for our case, we'd better try to make it higher and avoid the capacitors. 

  • 0 in reply to Shadow He
    Prodigy 30 points

    thank you mr.shadow !
    another question please.. is there a recommendation for a specific thermal paste to use it between the thermal pad and the heatsink surface?

  • 0 in reply to Imad Shaham
    TI__Mastermind 39830 points

    Hi I. Shaham

       The distance between heatsink and device's thermal pad would be more important than the specific thermal paste. If the heatsink is well designed could fit closely to the device, the distance would smaller than 0.1mm. In this case, no matter use which thermal paste, won't have large difference. Some customer use thermal silicon pad which may be more than 0.5mm thickness, that would affect the thermal performance a lot.