Hi Rick,
Thank You. We don't understand why it is working the way it is. The question we keep coming back to is what generates the timebase on the DRV8711. There are a lot of timing related functions on the chip but nothing about a clock in the block diagrams.
The maximum 1ms time for the current to decay seems to be a limitation for us. If we slow the step rate the current charges the motor coil more and takes longer to decay. If we limit the current we don't get our full motor torque. It has taken quite a bit of work to get it marginal.
Here is a trace of the same thing on a good board.
