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INA216: About maximum capacitive load

Toshiyuki
Mastermind 7075 points
Part Number: INA216

Hi,

I'd like to confirm about maximum capacitive load for the output of INA216. Our customer's board has a low pass filter, R=1kΩ and C=1nF for the output pin.Then, an oscillation problem has occurred.Should we put nothing on the output?

Best Regards,

Toshiyuki

  • 0
    TI__Mastermind 26620 points
    Hello Toshiyuki,

    Is the customer driving anything else with the INA216? Is it driving an ADC? What does the oscilliation look like?

    In the meantime here is a new application note on stability with current shunt monitors that could explain what customer is seeing.
    www.ti.com/.../slya029.pdf


    Best,
    Peter Iliya
    Current Sense Applications
  • 0 in reply to Peter Iliya
    Mastermind 7075 points

    Hi Peter - san,

    Thank you for your reply. Our customer is driving the CMOS gate of anything. So far, I haven't got the oscillation data. Anyway, should we replace either larger resistance or smaller capacitance for the low pass filter?

    Best Regards,

    Toshiyuki

  • 0 in reply to Toshiyuki
    TI__Mastermind 26620 points
    Hey Toshiyuki-san,

    The CMOS gate could contain significant capacitance adding onto the 1nF. Also is the current being measured changing or being modulated? Or is this low-pass filter on the ouput for noise?

    Sincerely,
    Peter Iliya
  • 0 in reply to Peter Iliya
    Mastermind 7075 points

    Hi Peter - san,

    I apologize for the delay in replying to you. This low-pass filter is used on the output for no reason. If customer use 1k ohm for low-pass filter on the output, which capacitor should be  selected? 

    Best Regards,

    Toshiyuki

  • 0 in reply to Toshiyuki
    TI__Mastermind 26620 points

    Hi Toshiyuji-san,

    You can use a 1nF or 100nF. I measured the output with 1kOhm/0.1uF using our EVM and there was no oscillation. I applied a 171.8mV differential on top of a 5V common-mode to the INA216A1 (gain=25V/V) and got a 4.28V ouput. The peak-to-peak noise is a noisy probe, but clearly there is clearly no oscillation.

    I would need more information regarding the circuit to understand why you are seeing the oscillation, but the Maximum Capacitive load specification in the INA216 datasheet (750pF) is meant for a purely capacitive load and no resistor on the output. So once you add in this 1kOhm resistor you can dramatically increase the load capacitor to ground without destabilizing your device.

    Sincerely,

    Peter Iliya

    Current Sense Applications