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UCC2895: Shoot-Through Issue with OUTA/OUTB on UCC2895

Conor
Guru 12115 points
Part Number: UCC2895

Tool/software:

Hi,

We are currently evaluating the UCC2895 in a prototype phase-shifted full-bridge power supply circuit.
During testing under light or no-load conditions, we have observed an issue where the MOSFETs connected to OUTA and OUTB experience shoot-through (arm short-circuit condition).

We are currently uncertain whether the root cause lies in insufficient phase margin in the voltage regulation loop or inadequate measures against MOSFET self turn-on.

As a countermeasure, we have attempted the following:

  • Slowed down the gate drive for the OUTB-side MOSFET (e.g., by adding series gate resistance)

  • Added a capacitor between gate and source of the OUTA-side MOSFET to suppress self turn-on

However, despite these efforts, the gate waveform on OUTA still shows a condition that overlaps with OUTB, resulting in a shoot-through event.

Would you be able to advise on possible causes or recommended countermeasures for this behavior?

If needed, we can provide oscilloscope waveforms and partial schematics for further analysis by private message.

Best regards,
Conor

  • 0
    TI__Genius 12795 points

    Conor,

    Please provide the schematic and corresponding waveforms.

    Thanks

  • 0 in reply to Ning Tan
    Guru 12115 points

    Hi Ning,

    I would like to send you the schematics of a custom board via private message, would you please allow me to do so?

    Thanks,

    Conor

  • 0 in reply to Conor
    TI__Genius 12795 points

    Conor,

    Mike will help from here. 

    Is there any reason why you cannot post here?

    If you'd like to share privately, I'd suggest to go through our FAE channel.

    Best,

    Ning

  • 0 in reply to Ning Tan
    TI__Guru* 86016 points

    Hello,

     

    The UCC2895 uses a turn-on delay to achieve ZVS on outputs A through D, you should not be seeing shoot through issues on the H Bridge.

     

    If you are using SRs your timing may be off causing what looks to be shoot through.  If you are using SRs you can verify this by disabling them to see if the issue goes away.

    If the issues is not with the SRs you might want to look at Out A, Out B, QBg and QAg to see if these FETs are being driven correctly with respect to Out A.  There may be a delay in your drive circuitry causing your shoot through issues as well.

     

    The following link will bring you to a reference design using the UCC2895 that show a schematic of how-to setup an application with SRs.  You can use this to compare to your schematic to see if there are any differences that could lead to y our shoot through issues.

     

    https://www.ti.com/lit/ug/sluu109b/sluu109b.pdf

     

    Regards,