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DRV8323RS: Vm swicthed off while vdrain is powered and high siede is on

Frank Matheis
Prodigy 20 points
Other Parts Discussed in Thread: DRV8323

Hello,

we are using the DRV8323RS Driver in several products and plattforms. To ensure a very low power consumation when electronic is turned off we also switch vm line of Driver while power Bridge and vdrain pin is supplied.

In some cases it happens that two high side Fets are turned on by Software and we switch of the vm line. I added a scope where you can see that vm line is slowly decreasing from 18V down to 10V (red line). Also I added the math function of gate voltage of high side by measuring gate voltage and substract the Phase voltage (blue line). Math result is shown in Purple line.

We see now that gate voltage also slowly decrease down to 2V Ugs until we make a disable of Driver.

Now our Question: Can any strange Situation happen in this Situation? we know from DRV8703 that VM must be in the same range than Vdrain. We checked datasheet of DRV8323 again but didn't find any Special Topic About.

Hope you can help us….

  • 0
    TI__Guru 61380 points

    Frank,

    We have cases where VM being higher than VDRAIN by more than 5-10V could cause issues but with VDRAIN being higher than VM, I don't think there will be an issue.

    I will confirm with design and get back to you.

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 20 points

    Dear Adam,

    thanks for your answer. We know About Problems when VM is getting higher you can get into Trouble.

    We have done a lot of measurements and found a strange Situation:

    When VM is decreasing while vdrain is stable and high side is turned on, on a voltage round About 20,5V we can switching glitches when are unwanted. Below 20,5V everything is fine and even if we rise voltage higher than 23V it gets also fine.

    I added a scope where you can see in red the VM line, blue is Phase node, yellow is gate voltage of high side and in purple the math calculation of gate voltage - Phase node.

    You can see two times switching of high side gate bevor Driver is disabled. This switching is unwanted switching and not performed from µController.

    Hope we can get an answer how we can colve this Situation.

    Frank

  • 0 in reply to Frank Matheis
    TI__Guru 61380 points

    Frank,

    Are you seeing any FAULTs during this time frame? Have you checked the VCP voltage and VM voltage near the DRV during this time?

    I suspect there is an undervoltage or charge-pump issue.

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    TI__Guru 61380 points

    Frank,

    I have seen no update on this thread, did your issue get resolved?

    I will mark this thread as closed for now but please post again if you need further assistance.

    Regards,

    -Adam