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UCC28950: No output for new PCB version

FRANK1
Expert 8535 points
Part Number: UCC28950

Hi Team,
 
Customer has a problem when he is using UCC28950PWR,
The old version PCB board can work normally, but the PWM output pin of the new board has no output and cannot work normally.

The pins 1, 5, 6, 7, 8, 9 and 10 of the old PCB version that can work normally are all high level in different degrees (pins 1 and 5 are high 5V level, and other pins are 2.5V level),

The ripples of these pins in new PCB version that cannot work properly are shown in the attachment.

[P1 Vref ripple]

[P5 SS/EN ripple]

The schematic diagram and PCB layout of the new and old PCB boards are the same,

[Schematic]

[PCB compare]

VDD supply voltage is 12V (measured is 11.86v).

I don't know where there is a problem.
can you give me some suggestion for the reason?

thank you!

  • +1
    TI__Guru* 85676 points

    Hello,

    If your SS pin is cycling more than likely the design has an OCP fault or something is loading down the the SS pin.

    I would start by studying the voltage amplifier output, CS, SS, Vout and VDD.  Evaluating this pin should help you determine what is going on and how to fix.

    It also seems like the customer had one version of there design working.  You might want to ask them what changed between versions of the design.

    The following link will bring you to the user's guide for the UCC28950 EVM.  It has waveforms that the customer could study and compare to there design to help see what may be different in there design.  They may also want to order one of these EVMs to evluate.

    https://www.ti.com/lit/ug/sluub02a/sluub02a.pdf

    You and the customer may find the following application note helpful.  It goes throughs a detail design process of the UCC28950 and even how to properly set the ZVS timeing. https://www.ti.com/lit/an/slua560c/slua560c.pdf

    Regards,