Other Parts Discussed in Thread: AMC3330, AMC1300, AMC1200
Because of its capability of galvanic isolation, I wanted to use AMC3301 in a design for isolated shunt measurement.
However, I have to support two measurement ranges which should be facilitated by switching between two very different values of shunt resistors (one range would use a small mOhm shunt, the second range a rather high shunt resitor value in the range on hundreds of ohms.
Now, I found that the bias current of AMC3301 is very high which leads to a high offset voltage for the range using the high-valued shunt resistor. That leads to the necessity of calibrating offset out which would be fine when just done once but acutally If I switch between the shunts, I would of course have to do a calibration anytime I switch between ranges which is very user unfriendly. The dirty solution would be to duplicate the amplifier part and select the proper frontend but that is unfeasible because of the high price of the AMC parts.
So I checked the AMC3330. There is no free lunch, and the AMC3330 has very small input bias current which solves the problem using high-ohm shunt resistor but is a bad solution for small shunt resistances because the offset error of the AMC which dominates in this case.
Which made me think of how I could solve the problem of the high input bias currents of the AMC3301. I may overlook something obvious but how about placing a high-impedance In-Amp just before the AMC input. That would allow "buffering" of the shunt voltage? I am aware that I may loose some benefits of the AMC, but at the moment I do not see a better solution. Of course, selection of the "pre-amp" may be tricky and I would have to provide supply for the buffer amplifier which I gues cannot be provided my the AMC´s integrated DC/DC so I may have to switch to AMC1300 or AMC1200 (reinforced isolation is not required).
What do you think about this approach?
