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AMC1302: About LPF for input

Guru 10555 points
Part Number: AMC1302

Hello E2E,

If added RC-LPF on input side, the gain will decrease. I want to be able to calculate the gain when with used input LPF.
Does TI have referenceable documentation for it?

Regards,
ACGUY

  • Hi ACGUY,

    When adding an RC filter, there will be a voltage drop across the filter resistors as they are inline with the differential input impedance of the device. For example, if your RC filter consists of 2 10ohm resistors and a 10nF differential capacitor and you are using the AMC1302 which has a typ differential impedance of 4.9kohm, the expect voltage drop would be Vin*20/4920 and the expect voltage at the inputs would be Vin*4900/4920. 

    Another thing to consider is the frequency of the input signal and the cutoff frequency of the RC filter. RC filters start to attenuate (decrease) gain long before their -3dB point. I've attached a TINA simulation that can be used to illustrate this point. RC_Filter.TSC

  • Hi Alex,

    Thank you for answer.
    Could you provide min/max value of differential input resistance?
    It does not have to be a guaranteed.

    BR,
    ACGUY

  • Hi ACGUY,

    Happy to help! 

    +/-15% from typical is a good estimation. Also, if you have not seen it already, please take a look at our AMC voltage sensing calculator