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AMC1300: Isolated Voltage Sensing with AMC1303x25x vs. AMC1300B

Part Number: AMC1300
Other Parts Discussed in Thread: AMC1303, AMC1100, TEST, AMC1303E0510


The AMC1303x25x recommends the use of an extra resistor in series with the AINN input to minimize the error caused by the input bias current, when using the amplifier for isolated voltage sensing (R3' in Fig. 55 of AMC1303 datasheet). Other isolated shunt amplifiers, specifically AMC1300B and AMC1100, do not mention this requirement.The AMC1300B datasheet doesn't actually discuss isolated voltage sensing at all, except for recommending the AMC1311B for (unipolar) dc link voltage sensing. The AMC1300's Functional Block Diagram in the datasheet looks identical to the AMC1303's Functional Block Diagram.

I tested the AMC1303E0510 with a resistor divider of approximately 1.2MOhm and 1k, and found that the extra 1k in series with AINN was highly necessary. Note: I realize that the AMC1303x05xx isn't recommended for resistor divider voltage sensing, but that was the one I had at the time for a test board, and I'll use the 250mV version in the future.

So, my question is: is the extra resistor in series with AINN necessary on the AMC1300B (like what is recommended for the AMC1303x25xx)?



  • Hi Andrew,

    Thanks for your post!

    When doing resistor divider measurements such as these we recommend the extra resistor for devices with low input impedance, including the AMC1300B. Devices with low input impedance are typically used for current monitoring across shunt resistors, but they can be used for voltage sensing as well.