DRV8308: Hall Sensor Override

Hi John,

Is 111b a valid condition for this motor?
I am assuming it is not based on the description of the problem. So why are the halls reading 111b?

Hio Rick,

The customer has let me know:

In a nutshell, due to hysteresis in the motor's Hall sensors, in some cases, they can be susceptible to external magnetic fields and therefore initially read an invalid Hall state of 111b (which *should* never occur, but in some cases with our physical configuration, it does during startup). As soon as the motor moves even slightly, the Hall sensors start working correctly again and the motor runs fine, but because the initial reading is sometimes an invalid one, the DRV8308 does not try to force the motor to move, and so we're stuck. So we'd like to forcibly move it, even though we don't have a valid Hall sensor reading, because as soon as we move it, the Hall sensor will begin functioning correctly. You could think of it as being a similar problem to using back-EMF for commutation feedback - you can't sense the position until it's rotating, so you initially run it open-loop.

Regards,
~John

Hi John,

There may be a way to force the device with additional circuitry.

Some type of circuit to monitor for a 111b condition and momentarily override a hall during startup is required. This could be a mcu or dedicated logic.

If the halls are being monitored by an mcu and a 111b state is seen, the mcu can override one hall to create a valid state. This should cause the motor to move when enabled. After moving, the mcu can release the hall.

Hi Rick

Thank you for your quick responses and feedback on this.

Unfortunately, the customer has tried this and it doesn't work in their situation. They are continuing to look into other ways to fix this issue.

Regards,

~John