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DRV8432: Is switching G_VDD a good idea ?

Nicolas LAISNEY
Prodigy 30 points

Part Number: DRV8432

Hello,

I am using a DRV8432 to drive a 24V DC motor.

For safety reasons, the 24V is externally switched so that I can guarantee there is no power delivered when it is not required.

I use the same switch control for the G_VDD rail (12V).

We ran some endurance tests and the 12V rail eventually when shorted to ground. When disconnecting the G_VDD pins from the 12V rail, the 12V came back to normal so the conclusion is that the DRV8432 is burnt.

Is this a bad idea to switch the G_VDD off ?

Would it be better not to switch the G_VDD (keep it to 12V all the time even when the P_VDD if off) ?

Thanks,

Nicolas

  • 0
    TI__Guru** 114905 points
    Hi Nicholas,

    What are the inputs during this endurance test? Are you using the recommendation of section 9.3 System Power-up and Power-down Sequence of the datasheet?

    When the device is operational, what is the PWM frequency and the BST_x capacitor values? Do they conform with section 7.3.2.1 Bootstrap Capacitor Undervoltage Protection of the datasheet?
  • 0 in reply to Rick Duncan
    Prodigy 30 points
    Hi Rick,

    thank you for considering my issue.

    During the test, the sequence is as follows:
    - Cold start :
    - Reset hold low (device inactive);
    - G_VDD and P_VDD are 0;
    - Mode set to 0 (Dual full bridge with CBC);
    - PWM frequency is 50kHz;
    - G_VDD and P_VDD are activated (12V and 24V respectively).

    Start of sequence :
    1. Forward sequence :
    - PWM ratio set to 75% on PWM_A (and 25% on PWM_B, to be complimentary)
    - Release Reset AB
    - Run for ~1min
    - Little pause : Assert Reset AB (device inactive), for ~30sec
    2. Backwards sequence
    - PWM ratio set to 25% on PWM_A (and 75% on PWM_B, to be complimentary)
    - Release Reset AB
    - Run for ~1min
    - Little pause : Assert Reset AB (device inactive), for ~30sec
    Repeat this all night (at least, tried).

    I'm not sure, but there could be a little delay between actual Reset state change and PWM change since it is done through an I²C device which is not as fast and deterministic as an MCU GPIO.

    We suppose this is not due to overheating since the device is protected and we experienced this when we did not have our heatsink yet.
    Same for overcurrent, we had to raise the OC resistor to 24k instead of 39k after changing the motor.

    BST_x caps are 100nF.

    Nicolas