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DRV8350: VCP Ripple and Unknown Faults

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Replies: 3

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Part Number: DRV8350

Hello, 

We are designing a BLDC motor drive with DRV8350 and transistors CSD19538Q2. We are supplying VDRAIN at 60V and VM at 10V with an external regulator. We drive the transistors at 300/600 mA (IDRIVE = Hi-Z).

We are switching at 40 kHz.

At a current of 2 A we see an unexpected FAULT (VDS overcurrent protection is set at 0.7V, around 14 A). A few cycles before the fault, we see a high ripple on VCP voltage (it swigns from 9V to 7 V with an average frequency of 2kHz).

Is there any known issue with the Charge Pump when supplied from external 10V supply? Could exist any relation between the gate current and the charge pump?

Thanks for your help!

  • Ricard,

    The FET mentioned has a Very low Qgd which is the dominating factor in deciding the IDRIVE setting. I would say that this IDRIVE setting is way too high given the Qgd of that FET. 

    Are you using any gate resistors in your design?

    What is your needed SHx rise and fall time?

    Please check this FAQ I've made which discusses deciding IDRIVE settings: https://e2e.ti.com/support/motor-drivers/f/38/t/796378

    In the past we have seen VCP getting pumped up which results in excess gate voltage and potentially device faults. The reason for this is that when IDRIVE is too high the gates and switch node tend to ring/overshoot/oscillate which can trip the VDS or VGS protection.

    If you lower the IDRIVE the problem will likely be fixed.

    Regards,

    -Adam

  • In reply to Adam Sidelsky:

    Ricard,

    Please also share your schematic if possible.

    Regards,

    -Adam

  • In reply to Adam Sidelsky:

    Hello Adam,

    Thanks for your answer and the FAQ information (very interesting!).

    We have reduced the IDRIVE current and the problem has been solved. 

    Best Regards,

    Ricard

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