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DRV8881: Driving a heater module

TJ Cook
Prodigy 30 points

Part Number: DRV8881P

So, we have a board that uses a bank of DRV8881Ps to drive a number of motors without issue.  Now, we are looking to reuse the same board to drive some resistive patch heaters (with pwm from our controller).

However, according to testing performed when we first brought up the boards, it looks like there are some issues when we try to drive a purely resistive load.  It seems to want to engage current-limiting mechanisms or something along those line despite never actually reaching overcurrent.
So, we can't find any specification in the datasheet which indicates a failure or limiting mode at high di/dt.  Is that a hidden spec?  If so, is there any hope for reusing this part to drive our heaters, or do we move on?

  • 0
    TI__Guru** 114905 points

    Hi TJ,

    What is the resistance of the load?

    What is the supply voltage, VREF, and current sense resistor?

    Are you monitoring nFAULT? If so, is nFAULT asserting?

  • 0 in reply to Rick Duncan
    Prodigy 30 points
    Hi Rick,
    The information I'm working with is a bit second-hand and was only documented in memory. I have enough confidence in the tester, that the setup was configured appropriately to not actually exceed the designed current limit. Nonetheless, I'll be checking back on those specifics you ask, and also try to replicate the test on my side.

    In the meantime, are you aware of any precedent for driving resistive loads on this part or others in its family?
  • 0 in reply to TJ Cook
    TI__Guru** 114905 points
    Hi TJ,

    Others in the family have driven resistive loads. Typically it is not a problem as long as the current does not exceed the chopping level. If the current exceeds the chopping level, the outputs will typically turn on for the blanking time (900ns to 1.8us) and then immediately enter current regulation.
  • 0 in reply to Rick Duncan
    Prodigy 30 points
    Hi Rick,

    Apparently my trust in the knowledge of others has been misplaced. I managed to dig out an evaluation board, and it appears it can drive resistive heaters without issue after all.