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TCA9539-Q1: EPAD (Pin25) Electrical Connection to Vcc or GND?

Gary Andrew
Prodigy 50 points
Part Number: TCA9539-Q1

Hello,

I'm considering using the TCA9539-Q1 in a new design.  I've studied the datasheet and can't find any statement on the electrical connection for the Thermal Pad, pin25, for the VQFN & WQFN packages.  On some products, the EPAD connection is GND but some use Vcc.  Please confirm what the electrical connection for the Thermal Pad, pin25, on the TCA9539-Q1 VQFN & WQFN packages.  (When possible, please update the datasheet to include the information.)

Thank you for your assistance!

Gary

  • 0
    TI__Mastermind 46788 points

    Hi Gary,

    I am reviewing the TCA9539-Q1 datasheet and don't see a VQFN or WQFN package option for a thermal pad. Currently, I only see the TSSOP variant of the device. I think you are referring to the non-auto qualified device.

    In general, thermal pad connections are normally labelled as NC (no connect) meaning they have no internal connection to the IC. 

    In most cases for layout, I recommend that the thermal pad either be connected to a large plane such as GND or VCC. The GND plane is more common due to the fact that it is usually a larger plane which allows heat to dissipate from the core of the IC into the metal plane on the PCB, thus many people connect the thermal pad to a GND plane. 

    Another description on this view point can be found in another e2e thread here.

    We would add a description telling customers to connect the "exposed center pad" to GND if it was always true. There are some circumstances where connecting to VCC would make more sense, so we leave this connection up to the customer. 

    Regards,

    Tyler

  • +1 in reply to Tyler Townsend
    Guru 316440 points

    The thermal pad is attached to the substrate, which is at GND (or the negative supply for op-amps). It is not specified whether this attachment is isolated. The pad can be connected to GND or be left floating; see [FAQ] Where do I connect the thermal pad of the logic QFN devices?

  • 0 in reply to Clemens Ladisch
    Prodigy 50 points

    Thank you for your response, Clemens.