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DRV8850 PWM micro pin count

Ian Barnes68507
Prodigy 210 points
Other Parts Discussed in Thread: DRV8850

Hello,

I am looking at designing in 2x DRV8850 into a product to replace an Allegro A3906. I need more current drive and the inbuilt LDO would be good too. The A3906 has 2 inputs (IN1, IN2) to control each full bridge, brake, coast, fwd, rev. A lot of similar drivers use this approach, or a DIR and PWM input. I am driving two DC motors in my product.

One problem I have is the DRV8850 requires 4 lines to control each FET on the bridge, this would be 8 lines from my micro instead of the current 4. This is a problem as space is at a premium on the layout. I wouldn't be able to use external logic to invert control signals.

I guess my question is, is there an elegant way to drive the DRV8850 with only two IO lines (both capable of PWM) to achieve forward, reverse and brake?

Kind regards,
Ian.

  • 0
    TI__Guru** 114905 points
    Hi Ian,

    Unfortunately, there is not an elegant way to drive the DRV8850 with two IO lines. There may still be a less elegant method.

    Are you using both DRV8850 devices at the same time? If not, can you set one DRV8850 in sleep mode and use 4 IO lines to control the other?
  • 0 in reply to Rick Duncan
    Prodigy 210 points

    Thanks Rick, in this case I cannot do that. But it was a great idea :-)

    If I am driving the 4 lines with PWM signals, does the device itself take care of deadtime? Is there an advantage to controlling the deadtime myself, or is it better to let the device manage it?

    Kind regards,

    Ian.

  • 0 in reply to Ian Barnes68507
    TI__Guru** 114905 points
    Hi Ian,

    The device does manage deadtime when switching. The combination of a minimum deadtime plus the slew rate resistor allows adjustment of deadtime.

    In general, there is no advantage to controlling deadtime yourself. In some instances, it can create more heat in the device as the current flows through the body diodes.