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DRV8350: High_Side FET turn ON when disabled

Guru 10320 points
Part Number: DRV8350

Hello E2E,

Our customer is using the DRV8350 for new product. They during to work H/W debug now.
They setted the device diable, they rotae the motor forced 2-turns by hand. The VM has rise to about 12V that 3 high_side FEAs became turn ON, like a shorted breaking operation.

Questions;
- When setted to disable, does internal CP-circuit has stop? or operating for continuously?
- When setted to disable, do protection features have stop? or operating for continuously?
- Does TI have any information for similar case with it?

Regards,
ACGUY

  • ACGUY,

    Thanks for your post!

    We do not recommend rotating the motor externally since the BEMF can damage the gates and source pins. Some of our customers disconnect the SH and GH/GL from the FET bridge when the motor is back driven to avoid this damage.

    Is your DRV8350 disabled or powered down?

    All logic and protection are disabled when the device is disabled or unpowered.

    Can you show a waveform of VM and the FET gates that are "on"?

    Regards,

    -Adam

  • Hello Adam,

    Thank you for reply.
    The VM was inputted, and the device was disabled settings.

    I thought that like a shorted braking operation is FETs protection function when conducted reverce current on body diode from S to D.
    Is this idea wrong?
    Please let me know the reason why FETs are turned ON under this condition.

    Best regards,
    ACGUY

  • Hello Adam,

    I confirmed conditions.
    Vin(Vvm) : Off
    Device : Disabled

    I tried items following;
    Case-1, Remove the TI IC ⇒ Phenomenon does not occur
    Case-2, Remove the gate resistance between TI's IC and drive FET ⇒ Phenomenon does not occur
    Case-3, Always set ENABLE of TI IC to DISABLE ⇒ Phenomenon occurs

    I obvserved a gate voltage of high_side FET by oscilloscope.
    The voltage is about 0.2V, not rise to Vth of FET.

    So, I anticipated ​that voltage rised up of gate for voltage wraps around the Gate by counter voltage.

    Question;
    Does this device have any root for counter voltage wraps around to the Gate?

    Please let me know your opinion.

    Best regards,
    ACGUY

  • ACGUY,

    Unfortunately the device does not have any automatic features to limit the gate or source current when the driver is unpowered or disabled.

    Some of our customers add a MOSFET in line with the gates and source connections so that they can disconnect them in cases where backdrive is needed.

    Another option could be to add a small FET to pull the gates and source lines to GND when they are not in use.

    Regards,

    -Adam

  • Hello Adam,

    Could you please use TI to reproduce the phenomenon that the High side FET turns on when the motor is forcibly rotated?
    Customers are in a hurry. Measures are required.

    Regards,
    ACGUY

  • ACGUY,

    We do not have enough information to recreate your setup.

    Please send an email to me about this and we can setup a conference call.

    Regards,

    -Adam

  • Hi Adam,

    I applied for friendship to you.

    Regards,

    ACGUY