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TAS6584-Q1: Thermal pad ground connection

Matthias Häfner
Prodigy 40 points
Part Number: TAS6584-Q1

Tool/software:

What is a proper way, to realize chassis cooling for the TAS6584?

According to the datasheet Table 5-1, the thermal pad is connected to ground.

Paragraph 11.1.3 states: "Heat-sink mounting screws, E, should be close to the device to keep the loop short from the package to
ground."

In terms of electrical performance, I would consider an anodized heatsink, pressed against the thermal pad with thermal compound in between a very bad and unreliable solution.
Electrically connecting the heatsink to the PCB ground plane with screws that are held by thread in bare aluminum I would consider equally bad.

I also would not want to electrically connect the thermal pad of the amplifier to the chassis in an automotive application. That could lead to uncontrollable ground currents flowing through the device.

So what is the reason behind that statement? Does the ground pad carry any significant current? Or is the gnd connection more like a shield to improve EMC performance?

Can I isolated the thermal pad from chassis ground and still reach the specified performance?

Thanks.

Best regards,

Matthias

  • +1
    TI__Mastermind 45045 points

    Matthias,

    The exposed thermal pad is not used as an electrical conductor.  We want it connected the heatsink to remove heat.  The heatsink should be grounded for safety.  We want the screws to be used for an EMI path from the thermal pad to ground.  A mounting screw is the best method to provide good thermal contact and a path to ground.

    It is normal in automotive audio design to have the ground plane on the pcb electrically connected the heatsink.  The heatsink is typically part of the chassis of the amplifier.

    I do not recommend isolating the thermal pad from chassis ground in an automotive audio amp.  Isolating will not impact performance, but you may have some trouble with mitigating EMI.

    I am assuming this is an automotive amplifier.  Is this for a different market?

    Regards,
    Gregg Scott

  • 0 in reply to Gregg Scott
    Prodigy 40 points

    Hi Gregg,

    thanks for getting back to me.

    Yes, this is an automotive amplifier. But it will be part of a more complex control unit that has additional high current switches on the same PCB.

    So I want to control where the return currents enter and exit the board.
    If I connected the thermal pad electrically to the chassis I would create a ground loop and would risk high currents going through the amplifier.

    We could put kind of a grounded shield on top the amp-IC and only connect that thermally to the chassis. But that would make the design more complex.

    I guess we have to figure out a suitable implementation ourselves.

    The important information for me was, that isolating the pad will not impact performance.

    Thanks a lot.

    Regards,

    Matthias