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DRV8711 Overcurrent Faults

Christopher Daily1
Intellectual 400 points
Other Parts Discussed in Thread: DRV8711, DRV8302

Hello TI E2E Team,

I have a customer that is running into some overcurrent phase faults using the DRV8711.  I read through most of the forum discussions but couldn't seem to find what my customer is running in to.  The motor can run for some amount of time before the faults triggers, seconds to minutes depending on current settings and motor loads and resonance. They have put together a very detailed summary of their issue in the attachment.  Any expert advise or assistance would be much appreciated!

Thanks Team!

Overcurrent Issue DRV8711.docx

  • 0
    TI__Mastermind 26065 points

    Hi Christopher

    Thank you of the description.

    Did customer read back the faults register? Just want to make sure the fault reported was overcurrent or PDF(predriver fault)?

    We will investigate this with the similar conditions and get back later.

    Best regards,

  • 0
    TI__Guru** 114905 points
    Hi Christopher,

    A few questions prior to digging deeper:
    1) How are Vmain and VBUS connected? Is there any voltage drop between the two signals?
    2) If the OCP fault only appears on the B side, is there something different about the layout that could cause this?
  • 0 in reply to Wilson Zuo
    Intellectual 400 points
    Hello Wilson,

    Thanks for the quick reply. They did read the Faults register and BOCP bit was on.

    Christopher
  • 0 in reply to Rick Duncan
    Intellectual 400 points
    Hello Rick,

    Thanks for the quick reply. The customer's response is below...

    Answers:
    1) There is a diode between them because a keep alive power supply can also power VMain when Vin power is lost, this keeps board logic alive. Vmain powers our voltage regulators. Vbus powers the FETs. We have had issue with our previous board using DRV8302 and on this board DRV8711 where if the keep alive power supply voltage happens to be even 1V above Vin the we get erratic behavior from the driver chip noticeable on the motor.
    and

    2) We tried to keep the layout clean because we have experienced crosstalk of processor PWM signal using the DRV8302. I can look closer if you see something happening in the screenshots.


    Thanks,
    Christopher
  • 0 in reply to Christopher Daily1
    TI__Guru** 114905 points
    Hi Christopher,

    Please ask the customer to compare the VM pin of the DRV8711 with the xOUTn pins when the fault occurs. It could be that VBUS is dropping while VM is remaining much higher.

    OCP is comparing the DRV8711 VM voltage with the xOUTn pin to determine the voltage across the high side FETs.

    If it is determined this is the reason, changing to a schottky from VBUS to Vmain (if a standard diode is used) may help. Beyond that, minimizing the voltage difference between VBUS and VMain when running the motor is key.
  • 0 in reply to Rick Duncan
    Intellectual 400 points
    Hello Rick,

    It was a voltage difference issue between Vbus and Vmain. Thanks so much for your help.

    -C
  • 0 in reply to Christopher Daily1
    TI__Guru** 114905 points
    Hi Christopher,

    Thanks for the followup. Glad that we could be of assistance.
  • 0 in reply to Rick Duncan
    Intellectual 400 points

    Hello Rick,

    There is one more thing the motor team could help assist with.  The same customer is trying to perform the same fix on their Servo driver. It uses the DRV8302 chip. They are trying to power the buck converter power supply from Vin through a diode to PVDD1, and power the gate driver PVDD2 pins using Vin directly. This way the Keep Alive input can power the 5V Buck regulator connected to board logic without powering the VBUS (PVDD2 and FETs).

    When they only connect power to PVDD1 the regulator does not work. It seems like it needs power on PVDD2 also to run. Is this correct? Or should this work method work?

  • 0 in reply to Christopher Daily1
    TI__Mastermind 21305 points

    Hi Chris,

    They have it flipped. PVDD1 powers the gate driver. PVDD2 powers the buck regulator. We have clarrified this in the next datasheet revision. It is OK for these power supplies to be at different voltage potentials.