TIDA035 October 2020
The operational amplifier is considered to be ideal in the above calculations. That is to say, the op-amp is assumed to be perfect with two main characteristics. The first one is that it has infinite input impedance resulting in ‘No current flowing into either of its two inputs’. The other one is that it has infinite open-loop gain resulting in ‘Two input voltages are equal without any offset’. However, real op-amps are non-ideal and have finite open-loop gain, finite input impedance, non-zero input voltage offset, etc. These non-ideal characteristics will affect the op-amp output voltage accuracy measured by ADC, as well as the insulation resistance calculation error. The errors of ISO_POS and ISO_NEG sampled by ADC determine the ultimate calculated insulation resistance error.