Controlling duty cycle of regenerative braking with MP6532 + Hall sensored BLDC

Hi there,

The MP6532 has a brake function that turns on all the low side fets. In my understanding this would cause the maximum braking torque to be applied to the motor. However we would like to vary the torque.
For decent low speed performance our application requires a hall sensored motor.

This seems to be possible with the controllers (MP6570 or 6710 for example), however I am unable to find how this would work with a hall capable pre-driver like the MP6532.

Any ideas on what components would work best together in this use-case?

Edit: the commutation table implies that changing the direction and modulating the PWM while the motor is running in the reverse direction could accomplish the same result. Is this correct?
Kind regards,

Julian

Hi Julian,

Thank you for contacting the MPS Forum. I am looking into this for you and should have an update for you soon.

Thanks,
Brendan Schoemehl
Field Applications Engineer
Monolithic Power Systems | MPS Now

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Hi Julian,

for Your decent low speed a sensor with a higher resolution makes sense:
Do You have discrete UVW block commutation Hall sensors?
or
Do You have a Hall based encoder for sensor?

Please check also our MPS position sensors: https://www.monolithicpower.com/en/products/sensors/angular-position-sensors.html
The MA102 https://www.monolithicpower.com/en/products/sensors/angular-position-sensors/ma102.html is a single device discrete Hall replacing sensors and the MA3xx https://www.monolithicpower.com/en/products/sensors/angular-position-sensors/ma302.html family does provide additional ABZ + SPI signals to the classic UVW signals.

Best regards,

Marko BDM sensors, EMEA

Hi Marko,

Thanks for your response.

With ‘higher’ resolution I assume you mean higher than sensorless (EMF based commutation)?

The motor has discrete UVW hall sensors (the traditional off the shelf variety included with industrial motors, NanoTec is the brand in this case), sadly we’d rather not change that right now so we have to deal with the hardware setup as is. Also our company prefers off the shelf components, so changing the hall sensors to a specific model is not preferred and custom ordering would incurr additional costs. What we would like is the ability to vary braking torque with a traditional hall sensor setup, that would be best. Changing the sensors is currently plan B.

Edit: or am I missing somtehing here and are you talking about a discrete device that is on the PCB not inside the stator?

Kind regards,

Julian Rutten

Hi Julian,

When Brake is active, the braking torque cannot be adjusted because brake logic (all low side FETs ON) is embedded. To brake the motor with variable torque, you can drive a PWM duty cycle that’s slower than the speed of the motor. The bigger the delta between real speed and applied PWM, the bigger the braking torque.

About the method of changing the direction and modulating the PWM:
You should not PWM in opposite direction while the motor is still spinning. It will overstress the driver.

Kind Regards,

Ling Han

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