Can you measure a floating voltage with a differential ADC

floating voltage reliably with it? Or are things going to drift and get unp redictable?

ltages for any pin are 0.3V above Vcc and below ground.

...

+2.5 volts to - 2.5 volts can be applied to the ADC. There is no reference to ground at any point from the source to the input and this includes all c omponents between including op amps. Nothing can be referenced to ground on the input side of the ADC in the full differential mode. The exception her e is the use of a "fully differential" op amp used as a buffer between your source the final input to the ADC. But you must be meticulous with this bu ffer to be sure there is no ground reference after the buffer." 20ADC.html

w its working with the source just floating in space and not being tied bac k to the ADC's common point in any way.....

Floating does not mean isolated. The differential voltage must be defined r elative to ADC COM.

** Really ?

When speaking of a signal source, the terms are normally synonymous.

If "floating" does not equal isolated then do enighten us as to what it does.

** Just as ambiguous as your first unsupported assertion.

... Phil

** A "floating source" has no conducting path to anything so references itself to whatever it is connected to.

Usually, the source is electrically shielded to prevent static charge build up or capacitive coupling of unwanted voltages that might harm the receiving amplifier's differential inputs or exceed their common mode range.

If need be, a leakage path to ground form each input can be created with a pair of high value resistors.

Similarly, a "floating measurement" is made when the test instrument has no conducting path to anything - like a battery operated DMM.

... Phil

It's probably a "flying-cap" circuit, so as long as the signal doesn't go above/below rails, it's fine... and the ESD diodes provide the leakage to ensure that condition with a floating source. ...Jim Thompson

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When you state you have a -2.5V floating voltage source, you fail to indicate the common mode of the signal.

What this "website" should write is "In the fully differential mode, any differential voltage from +2.5V to -2.5V can be applied." Note that you can't violate the common mode range of the inputs. That is each input can't exceed the rail by 0.3V. In this case, I am not referring to a differentially applied voltage, but rather the voltage on each pin.

If the part truly needs a dedicated website, well something must be lacking in the data sheet. [I'm not saying that is the case since the manufacturer's data sheet was clear regarding the limits of the analog inputs. There could be other issues that the supplemental website clears up.] However this supplemental website caused more confusion than it solved in this particular instance.

There are no floating ADC inputs, so the moment you connect the floating voltage source, it's clamped (at least) to the ADC chip's rails. It would be best (because your ADC might have some small common-mode sensitivity) to terminate at the ADC input, to some middle-of-common-mode-range potential. Things ARE unpredictable outside that range, and only get predictable again outside the absolute-limit range (you won't like the prediction!).

It would also be prudent to protect the expensive parts against static discharge from the originally-floating system, when it gets plugged in. This could be as simple as a plug-operated shunt switch (as found in many audio jacks).