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Original question:

UCC28780: ucc28780- exposed pad contact in prototype

UCC28780: ucc28780- exposed pad tests

robin gangopadhya18
Mastermind 6050 points
Part Number: UCC28780

Ulrich

So we had our 3rd proto built up & it  showed exact startup SWS & HVG. 

We pumped fist &  proceeded with further circuitry put in action to go for the PWML...nothing special ..just solder the xmfr .

BUT did not happen. I see  VSWS pin stuck at 2V ...no reason to push higher ..

WHY?

I suspect the exposed pad is cold soldered as it happened last week.

Is here a test we can do before  biasing to test for  exposed pad to PCB pad connection by application of some DC at a strategic node in the controller without any damage?

As it stands now, we have to undo all additions , reflow the pcb hoping to get good solder flow inside.

A test will be highly useful, if it existed.

robin

  • 0
    TI__Expert 8210 points

    Robin

    Our application expert on UCC28780 will reply to you early next week.

    In the meantime we recommend you review this debug app note guide for UCC28780 to help debug your design https://www.ti.com/lit/an/slua982/slua982.pdf 

  • 0 in reply to Eric Faraci
    Mastermind 6050 points

    Eric

    thnx for the information.

    Ulrich had already sent us this document.

    Our issue right now is how the controller behaves if the exposed pad does not get properly soldered. Seems it fails to start yet there is a current through R22- approx 10 mA-- in SLUUBV6 eval kit document.

    Another burning question: does the controller get damaged if the exposed pad is not connected correctly to the ground plane underneath the part during reflow.

    Yeah, Ulrich was waiting for the IC persons to get back with some information.

    Hope to hear back soon.

    -robin

  • 0 in reply to robin gangopadhya18
    TI__Mastermind 26770 points

    Hello Robin,

    Sorry for the delay; I was out-of-office much of last week.

    The designer confirms that there is NO bad behavior of the controller or damage to it if the thermal pad is not soldered to GND.
    But it is recommended to do so anyway. 

    However, lack of soldering will not account for the issues you have been experiencing with VDD stuck at 2V.  I will address that in your other thread, and close out this one concerning pad connection in general.

    Regards,
    Ulrich