Texas Instruments MSC1210 - Manual (Page 161)

Ratiometric Measurements
12-25
Analog-to-Digital Converter
12.16.1 Differential V
REF
One application would be a system where the measurement and the ADC are
on different grounds. Normally, you might have a voltage source that connects
to a sensor, and the bottom of the sensor connects to the reference resistor.
However, with two grounds, that can be different by more than 0.3V—that does
not work. In such a case, you will need to connect the reference resistor from
the power supply to the sensor, and then connect the sensor to GND2. Now
you can still use the reference resistor to set the reference voltage, even
though the voltages are between 2.5V to 4.5V.
The differential reference inputs, however, can be used for both grounded and
non-grounded applications. For example, you might have a sensor that must
be grounded (because of mechanical mounting). In that case the excitation
could go through the reference resistor before the sensor.