The output voltage to drive superconductor coils generally in range of 0 approximately 10V. for get 0.1% precision, the resolution of ADC can be better than 5mV in worst case for a 5V full range ADC. The output data can vary 66 for a 16-bit ADC with 5V full input range if input voltage vary 5mV. This is designed to meet 0.1% precision requirement. A single end input ADC was proposed in here since full differential ADC driver has DC-bias error. The large current capacity MOSFET has slow switch time than small capacity MOSFET, so the switching frequency in this specific application less than 300KHz in generally. Then a 1MHz sampling ADC is fitted for this application.

ADS8329 is a low-power, 16-bit, 1-MSPS analog-to-digital converter (ADC) with a unipolar input and excellent DC performance. The ±1 dB INL allows customers to monitor DC output voltage with high precision. The device includes a 16-bit capacitor-based SAR ADC with inherent sample-and-hold and uses an external reference. This allows customers to use external precise references and get better precision. The SPI of ADS8329 can be implemented with a daisy chain to save SPI. Refer Figure 3-3. Thus 4 SPI of TMS320F28384D is designed to drive 6 ADS8329.

A resistor divider potential need adopted since the maximum output voltage is 10V and beyond ADC full input range. Then a buffer has to be inserted to drive ADC. OPA182 is an ultra-high precision amplifier with zero-drift: 0.003μV/°C and ultra-low offset voltage: 4μV (maximum). This helps in keeping the controller to monitor output voltage with high-precision. The high-output current is also designed to drive the ADC directly and reduce the cost.