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DRV8832: Unable to drive motor

ed schriek
Prodigy 20 points
Part Number: DRV8832

Dear all,

I'm using a DRV8832 to drive a simple 3V brushed DC motor. The chip works as expected, I've connected LEDs to both outputs to verify the bridge control functionality. 

Now as soon as the motor is attached to the ouputs, things get a little weird, hence the reason I am here.
Lets say IN2=vss, IN1=vdd, i.e. forward. Indeed without motor, OUT1 is at vdd, OUT2 at vss.
With the motor connected OUT2 jumps to slightly below vdd voltage, hence very little current flows between OUT1 and OUT2, insufficient to drive the motor.

I've tried playing with VSET by connecting a potentiometer to it, allowing any VSET voltage between vss and vdd. This was without succes.
Furthermore the current limit feature is disabled (connected to gnd) and the fault pin is never triggered.

Any insight would be useful, note that I dont have access to voltage/current meters (I used a ADC on a stellaris launchpad to readout the voltage)

Thanks

  • 0
    TI__Guru** 114905 points
    Hi Ed,

    Do you have a scope? Capturing the outputs will help determine what the device is doing.

    VSET should vary between 0 and VREF, not VDD. Please make this change.
  • 0 in reply to Rick Duncan
    Prodigy 20 points

    Hi Rick, thanks for your reply

    I do not have a scope, I'm using an 12 bit ADC to read the voltage at the output.
    I made the adjustment, VSET is now between VSS and VREF, but no change.

    However, I might have discovered the problem; the chip is soldered on a MSOP-10 to DIP adapter.
    This adapter has no vias or whatever connection to the PPAD GND.
    I figured that the small GND pin resistance is too high for the current that the motor draws, causing ground bounce.
    I'll try to drill a hole in the adapter without destroying the chip and get back with the result.