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DRV10866EVM: Start-up sequence intermittent

Part Number: DRV10866EVM
Other Parts Discussed in Thread: DRV10866

Hi,

I am using the DRV10866EVM as a debug setup for my motor control. I am having start-up issues with one of two motors. The first motor has a phase-phase resistance of about 6.3 ohms and no center-tap. I am using a wye connection on the motor leads using 1.6k each to form a pseudo center-tap. When I used 3.2k the start-up wasn't as reliable.

Now for the problem motor. I am using the same driver setup with the same wye connection using 1.6k ohms. The phase-phase resistance was only 2.4 Ohm so I added 2 ohms to each motor lead to get 6.4 ohms phase to phase. The start-up is very erratic. It 'jogs' around in a full revolution and does this about 3 times before it "takes off" and starts spinning normally. The problem motor has an inertia about 1.5x the first motor.

The trace below catches a good startup on the problem motor. I'm triggering on Fg (Yellow). The center-tap is Purple 2v/div. The blue is one of the phase winding's. The time is 4ms/div.

The high frequency on the winding's is about a 6us period, which I assume is the DRV10866 processor (?). The PWM, not shown, is 25 kHz, 50% duty cycle.

*** Any suggestions to get reliable spin-up on first try?

*** Do I need AC filtering on the pseudo center-tap?