The third design is based isolated ADC, reference Figure 3-3. TI had released several isolated ADC to meet market requirements for measure high voltage or current with high common voltage safely. AMC131M01 is one of the parts as an excellent choice to meet current sensing for negative power supply. The benefits of AMC131M01 is that it integrated an isolated power supply and then simple the design, cost down and reducing total PCB area. Customers do not need to ever add another isolated power supply. The AMC131M01 also features an integrated programmable gain amplifier (PGA) that provides gains of 1, 2, 4, 8, 16, 32, 64, and 128. The internal reference voltage is 1.2V. Assume ADC result is D, gain of PGA is G, sensing resistor is R. Then the load current I is:

Figure 3-3 Current Sensing for Negative Power Supply Based Isolated ADC