TMS320F28377D: Can you use the 16-bit differential mode sensors on the F2837xD for single-ended inputs?

Joel Holland said:

If you are working with an application that requires 16-bit resolution to accurately measure an output voltage, can you use differential mode ADC to measure it even if it is not floating?

Please define floating with respect to this question.

Joel Holland said:

Is there anything wrong with just connecting the negative input of the differential mode ADC to analogue ground, such that you can measure 16-bit accuracy for a ground referenced signal?

This would violate the datasheet:

Hi,

Thanks for your reply. By not floating, I just mean that my source is single-ended in that it is a voltage measurement referenced to a ground. 

Is there any way at all to use the 16-bit differential mode to measure signals that are referenced to ground, without connecting the negative pin of the ADC to ground? Possibly by creating a small offset from zero and subtracting this value from the ADC measurement? This could be done by having say a 5V supply which is very well regulated, and using a potential divider to create a smaller voltage. Then the value is not zero and can be used in the differential mode?

From the document sent above, using 3V as VREFhi and 0V for VREFlo, Vcommon = 1.50V. With 50mV deviation either way, this gives a range of 1.45-1.55V. 
Does this mean that the sensor can only measure within this range? If you take 1.5V from 3V, you get 1.5V, and 1.5V above ground is also 1.5V. Surely the differential measurement cannot only accept values within this very small range of values?

Regards,
Joel

Joel Holland said:

By not floating, I just mean that my source is single-ended in that it is a voltage measurement referenced to a ground.

No, the differential mode requires both P and N references to be driven.

Joel Holland said:

Is there any way at all to use the 16-bit differential mode to measure signals that are referenced to ground, without connecting the negative pin of the ADC to ground?

Ground is not an acceptable N reference because it violates the common-mode voltage requirement that is centered around (V_REFCM).

Joel Holland said:

This could be done by having say a 5V supply which is very well regulated, and using a potential divider to create a smaller voltage. Then the value is not zero and can be used in the differential mode?

The Amplifiers Forum should be able to provide recommendations for converting a single-ended signal into a differential signal with a fixed common-mode voltage.

Joel Holland said:

From the document sent above, using 3V as VREFhi and 0V for VREFlo, Vcommon = 1.50V. With 50mV deviation either way, this gives a range of 1.45-1.55V. 
Does this mean that the sensor can only measure within this range? If you take 1.5V from 3V, you get 1.5V, and 1.5V above ground is also 1.5V. Surely the differential measurement cannot only accept values within this very small range of values?

Please see the TRM for details of ADC operation: