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DRV8350: MOSFET high temp. break down in high duty cycle

Yishan Chen
Intellectual 1380 points
Part Number: DRV8350

Tool/software:

Hi Team,

Customer now use DRV8350 in their e-bike application. Some issue happened, please see description below:

  • Working condition
  1. GHA duty cycle=98%, GLA duty cycle unnormally
  2. switching frequency=20K
  3. 3xPWM mode
  • Issue
  1. Low side MOSFET high temperature break down, the impendence to ground=7ohom
  • Waveform

(Green:GHA,Blue:GLA.RED:Phase voltage)

Could you please give us some insight about potential results?

Thank you,
Yishan Chen

  • 0
    TI__Mastermind 24616 points

    Hi Yishan,

    Today is a holiday in the US, but we will aim to provide a response soon.

    Regards,

    Anthony Lodi

  • 0 in reply to Anthony Lodi
    TI__Intellectual 1380 points

    Hi Anthony,

    Thank you for your respond.

    Could you please provide a answer by today?

    Thank you

    Yishan Chen

  • 0
    TI__Mastermind 24616 points

    Hi Yishan,

    It is possible that the low side MOSFET will never turn on at 98% duty cycle due to deadtime insertion needing to be taken into account as well as propagation delay. The waveform you provided is plausible given those factors, however I do want to point out that it looks like there is significant voltage coupling into the low side gate during high side MOSFET switching, which could potentially cause shoot through if the coupling is large enough. The phase voltage rise time is extremely fast, so I am not surprised there is coupling. I would recommend significantly reducing the IDRIVE to slow down MOSFET switching and reduce coupling into the low side. Additionally, adding Cgs capacitance can also help to reduce coupling. 

    When you mention low side MOSFET high temperature break down where the impedance to ground is 7 ohms, are you referring to the MOSFET gate to source impedance? Or drain to source? If you replace the MOSFET does the board work again? 

    Regards,

    Anthony Lodi

  • 0 in reply to Anthony Lodi
    TI__Intellectual 1380 points

    Hi Anthony,

    Thank you for your response.

    The low side FET refers to the push-pull driver inside of DRV8350.

    The external power mos is working just fine.

    Thank you

    Yishan Chen

  • 0 in reply to Yishan Chen
    TI__Mastermind 24616 points

    Hi Yishan,

    Thanks for the clarification! This is likely due to a GLx or SLx abs max violation on the low side driver that caused damage internal to the driver. looking at the waveform it appears that the rise and fall times for the MOSFET switching is quite fast and could be introducing significant overshoot/undershoot that could be violating the device specifications. In the waveform you provided, during high side MOSFET turnoff we see GLx drop below ground by about 2V due to dV/dt coupling, which could be stressing the pull down MOSFET. I would strongly recommend slowing down switching speeds to reduce transients. You could also consider adding some external Cgs and Cgd capacitance to further tune the switching. 

    Regards,

    Anthony Lodi