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TPS51215A: Ringing of high side MOSFET VGS and VDS

Tim Chen
Prodigy 10 points
Part Number: TPS51215A

For the high side MOSFET(PDC3908AZ) of the synchronous buck application(TPS51215A), we found that Vds and Vgs are ringing as output load is increasing. The amplitude of the ringing waveform at heavy load is bigger than at light load. But there is no ringing by using other MOSFET(NTTFS4C10N). Does the ringing syndrome relate to any MOSFET parameters?

The waveform is showed as below:

No load

Max load

  • 0
    TI__Expert 4670 points

    Hi Tim,

    I just checked the datasheet that you provided. Is there any external resistor added between the high side driver signal and the MOSFET? If yes, I would suggest to replace with 0ohm and try it again with MOSFET PDC3908AZ at heavy load.

    Also, could you try to increase the V5IN voltage to 5.2V and try it again with PDC3908AZ (recommended ABS max is 5.25V) at heavy load? I have some suspect on which parameters could affect based on the provided datasheet. I think those two experiments above can help to verify if my suspect is correct.

    Another thing is that the waveform attached is unclear... I could get little message from it.

    Thanks,

    Andrew

  • 0 in reply to Andrew Xiong
    Prodigy 10 points

    Hi Andrew, 

    There is 2.2ohm extenal resistor between MOSFET and high side gate. We also replace with 0ohm and it is also ringing. But we use PDC3908AZ as high side MOSFET and NTTFS4C10N as low side MOSFET and this combination is no ringing.

    Ringing waveform(Ch1: High side Vgs, Ch2: High sideVds)

    No ringing waveform(Ch1: High side Vgs, Ch2: High sideVds)

  • 0 in reply to Tim Chen
    TI__Expert 4670 points

    Hi Tim,

    Thanks for providing the clue. Could you help to measure the low side Mos Vgs and high side Mos Vgs at the same time when there is the ringing?

    Thanks,

    Andrew