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INA296AEVM: Low duty operation

Youhei Miyaoka
Expert 4635 points
Part Number: INA296AEVM


Tool/software:

Hi team,

My customer noticed that the FB result did not follow the current waveform at low duty. (Waveform distortion occurred below Duty4% at 1kHz operating frequency)

They think root cause is, the FB of the current monitor is output after judging the current direction (+/-) since it is a bi-directional type. Can you confirm customer thought is correct or not?
Is unidirectional current sense amplifier recommended in such situation?

Regards,

Youhei MIYAOKA

  • 0
    TI__Mastermind 32790 points

    Hello Youhei-san

    Can you please show scope shots?  Also a schematic of how they using it would help.

    How are they driving the reference?  The schematic will help with this.

    I don't understand why the output with lower duty cycle unless it is due to the VCM transition.  If this is the case I would suggest the INA241 which has the PWM rejection.

    Regards,

    Javier

  • 0 in reply to Javier Contreras4
    TI__Expert 4635 points

    Hello Javler,

    Thank you for your support. My customer shared me schematic and its waveform. Can you refer attached excel sheet and give feedback to them please?

    Regards,

    Youhei

    INA296A2-Q1動作確認.xlsx

  • 0 in reply to Youhei Miyaoka
    TI__Mastermind 32790 points

    Hello Youhei,

    The issue here is that the INA296 reaches the saturation at the output (swing low) and recovering from that is the issue. 

    • There are a few ways to fix this.  One is apply a reference voltage larger than the swing low value.  
    • Apply a negative voltage on the GND pin of the INA296 and leaving the Ref pins at GND.
    • Purposely create and offset by adding a resistor on the negative input pin.  (not recommended)

    Regards,

    Javier

  • 0 in reply to Javier Contreras4
    TI__Expert 4635 points

    Hi Javler, 

    Thank you for sharing workaround for this issue. 

    Can you explain why this saturation occurs? Sorry I can't understand this phenomena mechanism. 

    Regards,

    Youhei

  • 0 in reply to Youhei Miyaoka
    TI__Mastermind 35140 points

    Hi Youhei,

    Saturation occurs when the input differential voltage is equal to or below 0V. Under these conditions, the output will try to go to 0V and below as well, but clipped to close to ground due to physical limitations.

    As input differential reverses direction, the output will come back, initially slowly (relatively speaking) but then often overshoot. This appears to be the situations here.

    Customer could apply a fixed voltage to REF1/2 pins, such as 1V, to see if the problem improves.

    Regards

    Guang