Can I drive a bridge sensing circuit with a voltage reference?

Question

On the specification sheet there is this application circuit where the sensing bridge circuit is driven by the same voltage reference IC that sets the voltage reference (REFP) of the ADC.

I remembered being told that any voltage reference IC should not be driving any circuit with it, and its sole purpose is the set a voltage with minimal output current (e.g. setting REFP of an ADC). I did a quick search on voltage reference IC. Most VREF IC I found can output at least 10-25mA of current - more than sufficient to power a simple bridge circuit that worths a few hundred Ohms or more. So I don't understand the argument that the bridge has to be separately excited.

Is it a common practice to drive a bridge setup with the same voltage reference IC that sets REFP of an ADC to lower component counts?

Answer 1

Yes, it's ideal to use the same reference (with or without a buffer) in a bridge measurement. That way the reference voltage cancels out in the ADC reading.

As far as not drawing current from a reference- if you want the maximum performance you want to minimize the current draw and to have it steady (since the die temperature variations will affect the reference voltage and the load regulation will not be perfect). However, it's not always necessary to get the maximum performance, maybe you can meet specifications with a simpler circuit. So it might be a rule of thumb, but such rules are made to be broken, with due consideration and knowledge.

In this case, drift in the voltage reference actually cancels out. Using two independent references would mean you are also measuring the differential drift of the two references, which is not ideal.