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DRV8886AT: Continuity check of stepper motor windings and H bridge failures

Part Number: DRV8886AT

We are using the DRV8886AT stepper motor driver in a fairly critical application.
The stepper motor may be in sleep/disable mode for long periods of time but when we do need to drive the stepper motor we need to be fairly confident it will work.

To this end we have included a pullup resistor (10k) on AOUT1 and a pull down resistor (10K) on AOUT2, the same is done for BOUT1 and BOUT2.
What I was expecting while in sleep mode or disable mode is, the output drivers will be switched off and the voltage on the windings (AOUT and BOUT) to be VM/2.
The pullup/pulldown will allow us to confirm continuity of the stepper motor windings and none of the H bridge drivers have failed short circuit.

However, the output voltage in either sleep or disable mode is limited to between 6V and 8V rather than VM/2
This is not a problem as it will still allow us to achieve our BIT confidence check.
What I would like to know is; the voltage is as result of a known characteristic of the DRV8886AT and that it is very unlikely to change significantly from one part to the next and that this characteristic will not change throughout the life of the part.

Your help with this will be very much appreciated

  • Pete,

    I would think this is a known behave. The internal high side gate drive circuit has a pull-down resistor on the FET's gate to make sure the high side FET is off during the sleep or disable mode. The pull-down resistor could change the external resistor divider output voltage if there is a Zener between the FET gate and FET's source (xOUT).  If I remember correctly, the resistor could be tens kiloohm (BTW, we can estimate according to the VM voltage and the xOUT voltage). So, if the external pullup and pulldown resister is 10kohm, the voltage variation should be not very much.