TIDUEZ8 May 2021
The conditioning can be done through the calculation tool Isolated Amplifier Voltage Sensing Excel Calculator. The tool offers a detailed worst-case error analysis across temperature considering gain error and drift, and offset error and drift, and nonlinearity drift. Note that the error analysis is output referenced.
Hence, the errors in the analog front end, come mainly from the offset voltages of the AMC ( ) and the TLV6001 ( ), and the gain error in the internal gain of the AMC ( ) and in the gain set by the resistors in the differential-to-single-ended conversion ( ):
The results in Section 3.4 show that with the actual signal chain and resistive bridge, asymmetrical faults are detected with less than 3% error, symmetrical faults with less than 5% error, asymmetrical warnings with less than 3% error and symmetrical warnings with less than 3% error. If higher accuracy is desirable, precision op amps can be used for the differential-to-single-ended conversion, such as the TLV6001 pin-to-pin compatible OPA320 (Voffset 0.15 mV).If even higher accuracy on the isolation voltage readings is needed, a stand-alone precision ADC out of TI’s family can be used for this application. A differential input ADC could be used for this purpose, as there would be no need for a differential-to-single-ended pre-stage. Moreover, in this reference design the internal 12-bit ADC in the TMS320F280049C was used, which leads to a step size of 0.8 mV. Higher accuracy ADCs with 16-bits could be used for better precision.
The aim of this reference design was to show that good accuracy can be achieved with a cost-efficient solution.