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INA219: schematic design

David Zhao
Intellectual 1820 points
Part Number: INA219
Other Parts Discussed in Thread: INA210

Hi

My customer is adopting INA219 solution.  VIN+ is 12V from DC-DC, switching frequency is 250KHz. RSHUNT is 2mohm. Is it necessary to add filter circuit in input of INA219? If yes, what is required R and C value? Thanks!

Regards

David

  • 0
    TI__Mastermind 26750 points
    Hey David,

    I assume that the Vin+ input of the INA219 is connected to the power rail after the power IC's compensation circuit. If not and INA219 is inside the compensation circuitry of the power chip, then you do want to be careful with these filter values and know that our part probably would not work in this situation.

    Anyway with the INA219 outside of this compensation circuitry, it is most likely is not necessary to add the input filter. You can read this in the datasheet Section 8.4.1, but the input filter is only really necessary if transients of 1MHz or other greater harmonics of the 500kHz ADC sampling frequency are expected in the current you are measuring.

    What is the magnitude of the 250kHz switching frequency ripple? There is a tradeoff of error here. If you do not add an input filter, then your accuracy could suffer from the CMRR of the part at 250kHz, which is not listed in the datahseet, but should defintely not be lower than 40dB at 250kHz. However, if you add the input filter, then your accuracy will suffer since the input bias current will interact with the series resistors to create a larger input voltage offset. This is why we generally recommend these resistors be less than 10Ohms. Section 7.4.1 of INA210 explains this error analysis well if you would like to look there.

    Peter Iliya
    Current Shunt Monitor Applications