Error due to CMR for current sense amp

Discussion in 'The Projects Forum' started by RamaD, Mar 28, 2014.

  1. RamaD

    Thread Starter Active Member

    Dec 4, 2009
    254
    33
    AD8206 current sense amplifier has a min. CMRR of 76dB (6310) and a fixed gain of 20. If my common mode voltage is 13.6V, then the worst case error due to CMR is

    13.6V/6310 = 2.16mV, referred to the input, or
    2.16mV * 20 = 43.2mV at the output.

    Will it be this high? Or am I calculating wrongly?
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    That sounds correct. Other current sense amps, such as this, have higher CMRRs if that's a problem.
     
  3. RamaD

    Thread Starter Active Member

    Dec 4, 2009
    254
    33
    Thank you Crutschow.
    Actually there was a problem with a uC based charger being designed by a friend. The current was 0.7A(!) when the charger breaker was off, though the shunt was on the battery side connected to the uC.
    I managed to get a pin compatible INA282, with 120dB CMRR, though the gain is 50. Thanks again.
     
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