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TAS5630B DKD package - grounding of heat slug & heatsink

Benjamin Hoogendoorn
Prodigy 10 points
Other Parts Discussed in Thread: TAS5630B, TAS5630

Hello,

I have a question regarding the grounding & thermal interface of the heat slug & heatsink.


I one of the several posts about the TASS5630B,  a TI engineer replied, saying that proper grounding of the heatsink is important because currents flow directly rfom the heat slug into the heatsink. If not grounded properly (impedance/inductance), the chip can get confused.

The datasheet of the TAS5630B says: 

(1) Achievable output power levels are dependent on the thermal

configuration of the target application. A high-performance
thermal interface material between the exposed package heat
slug and the heat sink should be used to achieve high output  power levels.

Most of the thermal interface materials available (greas, films) are NON conductive.
And even if they are conductive, the impedance will never be that low as in mili-ohms, so high swithcing currents can flow freely...

Are there some kind of thin copper foils maybe, that will do both jobs; compensating/filling the roughness of the heat slug & heatsink and thermal conductiviness?

Kind regards,
Benjamin Hoogendoorn
Designing a mono-aplifier with the TAS5630b DKD in PBTL for active subwoofer application

  • 0
    Prodigy 225 points

    I've been testing the difference between graphite-based electrically conductive (though not low resistance) and electrically insulating thermal interface materials with the TAS5630B.

    I've found that provided the heat sink is electrically grounded, there appears to be no problem with using a conventional insulating thermal transfer pad material.  I have seen no anomalous behaviour when doing this, though my application only is providing 120W of output power per BTL channel.

    Note that this was NOT the case with the original TAS5630 (ie, before the 'B' version).  This certainly gave problems as the power output was increased if the metal pad on the top of the package was not earthed.

    Perhaps TI updated rather more on the 'B' version than the data sheets tell?

  • 0
    TI__Mastermind 37045 points

    Hi, Benjamin,

    I would recommend arctic silver ceramique 2.

    This thermal compound has the correct properties for use with our audio power amplifiers.

    Ceramique has high thermal conductivity and high resistance to flow.  In addition, while it is nominally neither conductive nor capacitive, Ceramique can provide both adequate electrical conductivity and capacitance.  In TI systems Ceramique is applied in a layer that is compressed to 1 to 2 mils thick.

    reg,

    Paul Chen

    Audio Applications Engineer

    Dallas TX.

  • 0
    Intellectual 580 points

    we did some tests using thin copperfoil between the pad and the silicon ( isolating) thermal interface material . The copper was soldered direct on the pcb on one side. I saw no measurable difference concearning noise or distortion between the units with foil or without. If you use 4 layer board, ground impedance will be very low if the design is done properly. Besides that, BTL designs are less critical with respect to ground connections, the inductive energy from both output filters cancels eachother during switching cycle instead of flowing back to the supply.

    Beware of the minimum impedance of the 5630 in BTL, at 48V Vdd, 3.6 Ohms is the absolute minimum.

    regards

    Geert