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DRV8873: Current through Body diode by BEMF

masahiko shimizu
Guru 11235 points
Part Number: DRV8873

Hi,

Back EMF can be an issue if the motor turns while the IC is not powered.
About Phase node output pin, Abs Max Ratings is VM+1V in datasheet.
For example, BEMF is 12V by the motor turns while the IC is not powered.
Then, VM pin is up to 11.2V. This cause is to supply power by BEMF through body diode of internal high side FET.
0.8V is forward voltage of body diode(12V-0.8V=11.2V).

Here, I have a question.
Body diode of internal high side FET can be too hot at this time.
Can TI show the abs max ratings of body diode current?
How can we define acceptable body diode current of this IC at this time?

Best regards,
Shimizu

  • 0
    TI__Guru** 114905 points
    Hi Shimizu-san,

    We will investigate and reply by the Friday.

    The body diodes of the DRV8873 are designed to handle the peak re-circulating currents.
    If the current continues to flow, the junction temperature will increase.

    How long will the motor turn while the IC is not powered?
    How much RMS current will flow through the diode?
    What is the ambient temperature?
  • 0 in reply to Rick Duncan
    Guru 11235 points

    Hi Rick,

    Thank you for your support.
    I answer below.

    How long will the motor turn while the IC is not powered?
    →Approxy 0.6s.

    However, it depends on the situation. It might increase.
    How much RMS current will flow through the diode?
    →Peak current is 2.1A, RMS is 0.5A upto 1.0A.

    What is the ambient temperature?
    →MAX temperature will be 50C.

    Could you refer to the attachment file “20181205_DRV8873H-Q1.PNG”?
    We assume that the device doesn’t damage within TJ(MAX)=150C.
    So, as the conclusion, does it depend on heat dissipation?
    Is our recognition correct?

    Best regards,
    Shimizu

  • 0 in reply to masahiko shimizu
    TI__Guru** 114905 points

    Hi Shimizu-san,

    This condition should be OK as long as the device absolute maximum or minimum specifications are not violated.