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Tie thermal pad of LMP90080 to ground?

Robert Learney
Intellectual 280 points
Other Parts Discussed in Thread: LMP90080, LMP90079

Hi all,

My board design would be so much easier if I could tie the thermal pad of the LMP90080 to ground. Is this possible or would it degrade performance?

Many thanks,

-Rob.

  • 0
    Prodigy 150 points

    Robert,

    I too am looking for this information, but on the LMP90079. The datasheet says on page 5, that the pad should be floating. However, the reference design on page 60 shows the pad tied to ground. I'm not sure which to believe.

    I did discover, through a PCB manufacturing error, that the thermal pad doesn't like being tied to the SPI clock. :)
    The clock was driven by a 3.3 V source, but it would not go above 2.5 volts on the scope. It also had a lot of capacitance.
    I'm sure TI never intended the thermal pad to have a 5 MHz square wave on it.

    Jason Pittenger

  • 0 in reply to Jason Pittenger
    TI__Genius 16890 points
    Hello,

    Yes, the thermal pad should be left floating.

    The picture in the datasheet will need to be corrected.

    Mike
  • 0 in reply to Michael Stout
    Intellectual 280 points

    Interesting - I've tied it to ground in my designs and all seems to be working well :) Certainly makes my design easier anyway instead of punching via chimneys through my internal layers.

    How much heat does this device need to dissipate anyway?

    Cheers,

    -Rob.

  • 0 in reply to Robert Learney
    TI__Genius 16890 points
    It does not dissipate very much heat. You would need to calculate it out for the way you are using it (supply voltage, supply current, current sources on or off, sps rate...) but I have never seen a part in use that was warm.

    We were told by the designers that the pad should be floating. They may be concerned about a parasitic gate being formed in the silicon when it is grounded. But as you mention, it certainly seems to work well in that state.

    Mike
  • 0 in reply to Michael Stout
    Prodigy 150 points

    Mike,

    Thank you for the clarification.

    In our application, we are not using any of the current sources and the part never gets warm.  

    Jason.