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DRV8412 - DRV8432 RESET pin behavior

Michael Bech
Prodigy 30 points
Other Parts Discussed in Thread: DRV8412

Hi,

I plan to use the RESET pins of the DRV8412 / 8432 to force the controller into high-Z state in order to get this kind of operation:

1. Set up PWM duty cycles; Enable chip using RESET pins; run variable duty cycle PWM @ approx 100 kHz switching frequency for about 2 ms;
2. Disable chip using RESET pins to force all output MOSFET's to the off state; keep chip in off state for 20 ms
3. Go back to state 1

Basically,  the missing information about the RESET pin latency is answered by Rick in this post https://e2e.ti.com/support/applications/motor_drivers/f/38/p/449494/1616134  where 50 ns has been measured.

However, the chip was most likely not intended for the kind of operation that I need, so my basic question is whether or not the described operation will work  - or do my planned use of RESET add some extra stress to the device that can lead to malfunction?

Thanks,
-Michael

  • 0
    TI__Guru** 114905 points
    Hi Michael,

    This should work, although there are a few items to watch for.

    Depending on the amount of current in state 1, disabling the outputs could cause PVDD to spike. Please ensure there is enough capacitance to prevent this.

    Are you PWM'ing the RESET pins during the 2ms? If you are, this can generate extra heat in the DRV8412 because the current is flowing through the body diodes.

    What is the planned voltage and current for the system?
  • 0 in reply to Rick Duncan
    Prodigy 30 points

    Hi Rick,

    Thanks for your quick reply - appreciated!.

    We plan to control the current to zero before disabling the device, but of course you are right that the voltage on PVDD needs to monitored carefully.

    The main reason for toggling between enabled and disabled is that we need to measure a back-emf generated by the load - which in turn requires all half-bridges to be in the off state. The RESET pins will not be PWM'ed during the 2 ms where the device is enabled.

    The peak current is around 7 A during the 2 ms period - so the average current is quite small compared to the ratings of the device. DC link voltage is 40 V.

    Hopefully, I'll get the setup completed in lab next week to test the drivers, but it's good to know that there is no major immediate risks.

    Kind regards,

    -Michael