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TPS23757EVM: Diode SPEC

Julian Chen
Expert 2550 points
Part Number: TPS23757EVM
Other Parts Discussed in Thread: TPS23757, TPS23758, TIDA-00617,

Hi E2E,

We use TPS23757 EVM to design.

Could you let me know what key SPEC  of diode?

  • 0
    TI__Mastermind 41770 points
    Hi Julian,

    Note the square wave from the gate2 pin is capacitively coupled to the data transformer then to the gate of the FET. U5 will clamp the negative pulse to close to secondary ground. The diode should at least be rated 2x the bias winding voltage and 200-300mA. It's forward voltage should be fairly low as well. We have used BAV99 in past designs as well if looking for an alternative part.

    For a 5V output though, I recommend looking at the TPS23758 which is a PSR synch solution. It will reduce your BOM
  • 0 in reply to Darwin Fernandez
    Expert 2550 points

    Hi Darwin,

    Thanks for you reply.

    Our customer Design follow TPS23757 EVM. they use BAT54S to replace BAV99
    (BAT54S Datasheet: https://www.diodes.com/assets/Datasheets/ds11005.pdf)

    After thet change to BAT54S, they get customer retun and find Q2 MOS and U5 diode overheat maybe lead to VOUT abnormal.

    My question is:

    Could BAT54S replace BAV99??
     

  • 0 in reply to Julian Chen
    TI__Mastermind 41770 points
    Hi Julian,

    We have used BAT54 in past designs with a slightly different gate drive design. Please see TIDA-00617. We have an extra series element. I recommend modifying your board to be similar to this design if wanting to use the BAT54. Otherwise, I recommend sticking to the exact same design as the EVM.

    Thanks!
  • 0 in reply to Darwin Fernandez
    Expert 2550 points

    Hi Darwin,

    Thanks for your reply.

    Could you let us know which parameter is critical point?
    We find the GAT2 waveform is abnormal at all. (Please refer the picture as below)

    Our customer want to know it! Thanks!

    Wavform: pin7 of IC(TPS23757 GAT2) with BAT54

    Wavform: pin 7 of IC(TPS23757 GAT2) with BAV99

  • 0 in reply to Julian Chen
    TI__Mastermind 41770 points
    Hi Julien,

    Note the difference in gate drive topology with the TIDA-00617 (using the BAT54) vs the TPS23757EVM (using the BAV99). The TIDA-00617 has a series element to drop the voltage at the diode. I either copying the same approach; otherwise, I recommend sticking with the BAV99 which will need a higher rated diode.