Hi Ben, This reference design can measure voltage or current signal. When the input is current signal(4-20mA or 0-20mA), the host controller commands TCA6408A to turn on or off the 200ohm resistor, switching TLP3123 by TCA6408A can connect 200ohm resistor to ground and convert 4-20mA current signal to 0-4V voltage signal which can be accepted directly by ADS8688 . If you do not measure current signal, you will not need the TLP3123. +5V_ISO is provided for DVDD of ADS8688 , the SGND is the ground for ADS8688 as well, and this ground is different from the ground on host controller side. This TIDU365 is an isolated reference design, please refer to below block diagram. Please check the schematic in Figure 37. Best regards Dale
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