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TCA6424 Thermal pad

Breno Rocha
Prodigy 200 points

Other Parts Discussed in Thread: TCA6424A

Hello,

Is the thermal pad of the IO expander TCA6424A electrically connected to GND or some other part of the circuit? The reason of my question is to understand if  I can use my PCB GND plane as the thermal dissipating area for the component. I mean, should I leave the thermal pad floating or can I connect it to GND?

Best regards,

Breno Rocha.

  • 0
    TI__Mastermind 30310 points

    Breno,

    The bond diagram DOES NOT show the Thermal Pad electrically connected to any of the pads on the package. I am checking with the packaging team to make sure this is true.

    Also, I unsure from your question: is it advantageous for your design if the Thermal Pad is electrically connected to GND?

    Regards,

    Brian

  • 0 in reply to Brian Berner
    TI__Prodigy 120 points

    Brian is correct. The device does not require, nor does it have an electrical GND from die to the exposed pad. It would be no advantage or disadvantage to ground your side in the PCB design. The GND from die substrate to pad through die epoxy is weak at best due to silicon oxide on back side of die.

  • 0 in reply to Frank Mortan
    Prodigy 200 points

    Actually, the advantage of connecting it to the ground plane is that I would have a bigger dissipation area of cooper than if I connect it to a floating plane. If possible, it would be good if that information is added to the component's datasheet.

    Thank very much for the help!!!!

    Best regards,

    Breno.

  • 0 in reply to Breno Rocha
    Intellectual 840 points

    At the bottom of the original PDF i found this note

    This package is designed to be soldered to a thermal pad on the board.  Refer to Application Note, QFN/SON PCB Attachment, Texas Instruments Literature No. SLUA271, and also the Product Data Sheets for specific thermal information, via requirements, and recommended board layout.  

    Then this PDF link


    http://www.ti.com/lit/an/slua271a/slua271a.pdf

    I would check the electrical conductivity from the center to each pin to ensure either ground or no pin connects to the center pad. ( as it does not show either way in http://www.ti.com/lit/ds/symlink/tca6424a.pdf )

    It does look like a center pad with through holes to a ground plane would be acceptable.  Particular attention to section 3.5 Solder mask to see with and with out tenting on the through holes.

    Either way, it is quite informative how to handle larger SMD devices in that PDF.

    Hope this helps,

    Eric

  • 0 in reply to Eric Blenner-Hassett
    TI__Prodigy 120 points

    The question was electrical connectivity from exposed pad to PCB GND plane. Not solder connection of exposed package pad to PCB center land. With QFN, you should always solder the exposed pad to the PCB center land.