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Isolating two DRV8711 for redundancy

Nathan Smith
Intellectual 620 points
Other Parts Discussed in Thread: DRV8711

I am working on a design that requires redundant motor driver circuits. One circuit will be energized (driving a stepper motor with 24V) while the other is not. This second circuit is located on a second circuit board which is not powered. However, both circuits are connected to the motor drive lines (AOUT1, AOUT2, BOUT1, BOUT2). Because of the clamping diodes on these pins of the DRV8711, the motor drive signals from the powered circuit are back-feeding into the power nodes of the unpowered circuit and causing problems. Would it be possible to put a buffer op-amp (or two in parallel) on each of these lines to help isolate them? The op-amps of the unpowered board would be unpowered and therefore not pass the undesired signal to the unpowered DRV8711, but the op-amps on the powered board would virtually invisible as long as the proper part were chosen.

Is this a viable solution?

  • 0
    TI__Guru** 114905 points
    Hi Nathan,

    Can you provide a little more information? When one board is back feeding VM through the body diodes of the power FETs, what problem(s) are you experiencing?

    We will investigate and reply soon.
  • 0 in reply to Rick Duncan
    Intellectual 620 points
    The node connected to VM is also used as the input voltage to lower voltage power supplies, which try to turn on, which in turn try to turn on other chips that they power. The unpowered board becomes partially powered which interferes with the operation of the intentionally powered board since there are several redundant circuits like this one. Outputs are fighting with each other, dogs and cats living together, mass hysteria.
  • 0 in reply to Nathan Smith
    TI__Guru** 114905 points
    Hi Nathan,

    Thanks for the clarification. If the control logic remains unpowered, would that solve the problem?

    If so, your main supply on one board could be split into two rails. One rail would power the control logic and the second rail would power the motor. The second rail would be behind a FET that is switched on when the control logic is powered. The control logic would then generate a signal to turn on the FET.

    There may be other problems to find.
  • 0 in reply to Rick Duncan
    Intellectual 620 points
    I am attempting to isolate VM and GND for the motor circuit behind some SSRs. I will check back in with the result.