10.2.2 Detailed Design Procedure for Remote Ground Tracking

In order to make the DAC outputs follow the remote ground, the best approach is to level shift the reference input. Figure 67 depicts a method wherein both the REF and REFGND inputs are level shifted with respect to DUTGND. However, as the DAC doesn’t allow the REFGND to become negative compared to GND, an offset voltage of 300mV needs to be applied as shown. This method requires an external 2.5V reference and a way to generate a stable 300-mV reference. A dual opamp U1 is used to shift both REFGND and REF by (DUTGND + 300-mV offset). Table 24 provides the nodal analysis of the circuit. As evident, the DAC outputs track the DUTGND with an offset of 300mV. This offset can be easily compensated in software. Note that the absolute max values between REFGND and GND must be respected. When the absolute max values are reached, they should only be for a transient period and not for sustained amount of time.