INA180: Can voltage dividers be used to extend the common mode range of a current sense amplifier?

Hi Randall,

this question is asked very frequently. The answer is: No. Manufacturing tolerances, uneven temperature drifts and long term drifts of voltage divider resistors will totally ruin the high common mode rejection of INA180. And even with a perfect match of voltage divider resistors any imbalance of input impedances of both inputs of INA180 will also ruin the common mode rejection.

The INA180 is designed to have a very small shunt between the two inputs. With this configuration both inputs see (almost) identical impedance "situations" and the common mode rejection will still be very high.

Kai

Thank you, Kai. Is there a similar part with a higher common mode voltage?

Randall,

We do have several parts that extend a higher common mode voltage. Our highest level of support today is the INA290, which supports up to 120Vcm. What level of voltage are you looking to support in the application?

Thank you, Carolus. The application requires 34 V, just a bit higher than the INA180.

Hi Randall,

only to show what CMRR has to be expected with real world voltage divider resistors. +/-0.1% manufacturing tolerances, +/-0.1% temperature drift and +/-0.1% long term drift is assumed in the following simulation. 1k resistors were just chosen for simplicity:

randall_ina180.TSC

This is only the effect of imperfect resistors. Not shown is the additional imbalance introduced by the slightly uneven inputs of INA180 and/or layout imbalance, which only have an impact on CMRR when adding such a voltage divider. The CMRR of naked INA180, on the other hand, would be about 110dB.

Kai