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AD8643 Thermal Pad Connection

usama.i
on Nov 4, 2015

Hi,

This is a silly question, but what would happen if the AD8643 Thermal pad for LFCSP package is connected to Ground?

I think Pads are often connected to Ground, so while making a PCB design, I mistakenly connected it to Ground instead of V+ as specified in the datasheet.

The amplifiers seem to be working, but I have some issues with the overall circuit that I'm debugging. I wonder if this has any negative effects.

Thank you

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  • 0 on Nov 4, 2015 1:35 PM

    Hi Usama.i,

    Usually most pads are connected to ground for stability and thermal dissipation. But in this case, it is not. When the datasheet specifies that the pad needs to be connected to a particular supply, then most likely the thermal pad is electrically non conductive but not guaranteed.

    Please see this link for the thread similar to your question.

    It is stated there that: "In many cases you will see no difference if you connect the pad to the wrong supply connection but in some of the parts, there will be an electrically conductive path between the substrate and the electrical ground.  When this happens you will see increased leakage and may get unusual behaviour and reliability issues.  Definitely should be avoided in the design!"

    I hope this helps.

    Regards,

    Roel

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  • 0 on Nov 4, 2015 1:35 PM

    Hi Usama.i,

    Usually most pads are connected to ground for stability and thermal dissipation. But in this case, it is not. When the datasheet specifies that the pad needs to be connected to a particular supply, then most likely the thermal pad is electrically non conductive but not guaranteed.

    Please see this link for the thread similar to your question.

    It is stated there that: "In many cases you will see no difference if you connect the pad to the wrong supply connection but in some of the parts, there will be an electrically conductive path between the substrate and the electrical ground.  When this happens you will see increased leakage and may get unusual behaviour and reliability issues.  Definitely should be avoided in the design!"

    I hope this helps.

    Regards,

    Roel

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