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DRV425: using external reference and single-ended measurement vs internal reference voltage and differential A/D measurement

Part Number: DRV425

Your precision measuring circuit examples all recommend using a differential A/D measurement to subtract the (potentially drifting) internal reference voltage from the signal voltage.
Would a dedicated external precision reference voltage source, fed to the REFIN pin, and not using the internal reference, be potentially just as good and allow single-ended voltage measurement with comparable accuracy ? Or is it essential/required based on the architecture, current draw etc. to always measure the field and field changes as a function of (Vout - Vref), no matter if external or internal reference voltage is used ?

  • Hello Alexander,

    You could use a precision reference to deal with the potential drift that comes from the .  Since you are looking at more precision than what is given by the internal reference please also look at section 7.3.2 of the datasheet for the gain error as well.  Make sure your reference can drive the ~40kΩ load and understand the load will change depending on the input.  

  • Thanks. Thanks for pointing out the gain error as well. I need more "stability" than "absolute precision", so as long as an external precision reference with adequate current drive capability could do "better" than the internal reference. I am a bit constrained on differential inputs and if I can eliminate the drift of the reference with a more precise external one and thus use single-ended A/D, my life would be easier. I saw in a quick bench setup the reference change with field strength, and I assume this was indirectly caused by a larger current needed for the larger field compensation. I guess I will test and see....looks like your answer suggest I could do improve the drift a bit and thus maybe end up being able to use Single ended A/D.