I have not designed with that chip, and you haven't provided much detail, so take these as suggestions of places to look not as any sort of Gospel:
- Measure your supply current. If there's a bad fault it may spike right before shutdown.
- Check that the Hall output from the motor is hooked up correctly (there's six ways to hook it up; one is right).
- Check that the flavor of the Hall output matches the flavor expected by the controller chip. I can't remember which is which, but there are two popular ones; using the wrong one is -- wrong.
- Verify that you have no shorts to ground or power. Or anywhere else for that matter.
- Verify that your PWM is a good frequency. It needs to be high enough so that the coil current is limited by the coil inductance, but not so high that you're effectively shorting the output with the inter-turn capacitance of the coil. At a guess, 10kHz should work but that is a total wild-ass guess and is absolutely, positively not guaranteed.
- "PWM coming two phases at a time" is not unreasonable, if by that you mean that at any given time one phase is open-circuit and the other two are being driven by your PWM signal with opposite duty cycles.
I Have removed MODE=0, then the motor is rotating fine. but now the problem is, sometimes motor is not rotating. when i spin it with hand then it is rotating. the solution is there for A3931 but i am using A3930. please help me to find solution.
Maybe... instruct the controller to spin the motor very slowly; then instruct the controller to spin the motor slightly faster; then the same sequence till you're at the desired speed. Once again, maybe...
That would certainly be the appropriate thing to do if the motor is taking a while to spin up -- I don't know how that chip deals with speed commands that are way higher than the motor can do, or with over current events.