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INA296A: High side current sensing in the H-bridge and recirculation

Benyuan Liu
Prodigy 93 points
Part Number: INA296A
Other Parts Discussed in Thread: INA296B,

Hi, I am using DRV8432 (PWM switching frequency is 500KHz) to drive a voice coil and plan to sensing the current in the high side (as it is recommended in the datasheet).

Due to motor stop and brake, there might be recirculation current flowing inversely. 

Is it safe to use a unidirectional INA in this scenario (reduce the cost) or stick to use the bidirectional one (i.e., INA296) for HS current sensing? How should I calculate the safe margin during brake or slow decay?

  • +1
    TI__Mastermind 29530 points

    Hello Benyuan,

    The INA296 can have a negative input voltage if using it in unipolar configuration. The only thing is you may have to wait for it to recover from a saturated output.  This may not be much time but you need to be aware.  If you can tolerate a bipolar output you may change the VREF voltage to give you some room for you to use.  There is a lower cost option in the INA296B.  The speed of this device will also help in the recovery when then input is beyond its linear range.  

  • 0 in reply to Javier Contreras4
    Prodigy 93 points

    Thank you for your reply. I may not clearly describe my question.

    1, I found that in this article, The art of stopping a motor – VM pumping - Industrial - Technical articles - TI E2E support forums, Figure 2, during motor brake, there is an inverse or recirculation current flows from motor to PVDD. If I placed an CSA + Shunt at high side, the CSA we choose should be bidirectional rather than unidirectional, right? If so, the choice we had, BW>1MHz, bidirectional, only two CSAs left, INA241 and INA296.

    2, in order to get the bidirectional current from INA296A, I should adjust the REF as figure 8-6 in the datasheet. During recirculation (negative current), PVDD will rise from 40V to 50V, but the common mode voltage over the high side shunt resistors is still positive, and within the range of -5V to 110V, so it is safe to use INA296. Please correct me if I am wrong.

  • 0 in reply to Benyuan Liu
    TI__Mastermind 29530 points

    Hello Benyuan,

    Yes this is still able to be used.  The part I was warning about is using the INA241 or INA296 and using it in a unipolar mode and getting a negative Vsense.  This would cause the output to saturate to 0V when the current is negative and would take time to recover.  If you adjust Vref like you mentioned above this would be an issue.