Q: What is the input impedance of the MAX4372 current sense amplifiers?
A: The MAX4372 doesn't have a constant input impedance, but rather draws a fairly constant input bias current, so long as the input voltage remains above 2V. An effective input impedance can be calculated if you know the common mode voltage at the input of the device, simply by dividing the common mode voltage by the bias current. For instance, with a 20V common mode input, RS+ has a bias current of 1uA (max), so input impedance into that pin is 20MOhm (min). RS- has a bias current of 2uA (max), so under 20V it would appear to have an input impedance of 10MOhm (min).