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DRV8234: How can I implement sensorless position control for BDC?

Jennifer Jordan
Intellectual 1076 points
Part Number: DRV8234
Other Parts Discussed in Thread: DRV8214, ,

Hello,

I’m trying to do implement position control with a BDC motor but hall sensors are expensive and I can’t fit it in my mechanical design, do you have any motor drivers that can help with that?  

Maybe something that can drive a brushed DC motor like a stepper motor with precise position control without a sensor? I saw that there are a couple devices that might work, DRV8214 or DRV8234 but not sure how it works. 

  • +1
    TI__Mastermind 23421 points

    Hey Jennifer,

    Our new driver the DRV8234 or DRV8214 have exactly what you describe - Sensorless Position Control.  This is based on ripple counting.  When a brushed DC motor spins the brushes momentarily short out two adjacent commutators, and this short causes a rise in the motor current.  This periodic rise looks like a ripple on the steady-state brushed DC motor current waveform, and our devices can detect this small rise and track it.  This means our devices basically can replace an incremental encoder.  

    For precision, the accuracy depends on the motor construction.  Many small (<2A) BDC motors have 3 commutator segments and 2 brushes, which will result in 6 ripples per 1 full rotation.  Thus 60 degrees accuracy.  Often BDC motors have a gearbox so this accuracy is more than enough.  The accuracy also is best over longer motor runs - the device might miss 1 or 2 ripples on startup or slowdown, but during steady state it should track the motor position perfectly.  

    I recommend you order a DRV8234EVM to start playing around with it yourself! See the DRV8234 datasheet or the EVM User guide for details on how to configure the device/EVM and other options or features of the device.

    Regards,

    Jacob

  • 0 in reply to Jacob Thompson
    Prodigy 30 points

    I saw in the ripple detection section of the DRV8234 specification sheet that the attached figure introduces the integration of ADC devices inside the chip, but I did not find relevant indicators in the specification sheet. Can you provide an explanation of the dynamic performance parameters of current sampling and ripple detection? Thank you!

  • 0 in reply to Ryunosuke Akutagawa
    TI__Mastermind 23421 points

    Hey Ryunosuke,

    Could you elaborate on what parameters or performance description you're looking for? 

    And could you point me to where the reference is missing? I looked in the datasheet but couldn't find it.

    Best,

    Jacob