FRDM-K22F 16-bit ADC output format in differential mode

[davepfaltzgraff]

I'm using the 16-bit ADC on a FRDM-K22F board to measure a differential signal. If the ADC references are 0V and Vcc, and the DADM0 pin is tied to Vcc/2, then I would expect the result of any conversion would fall between -32768 (0x1000) and 32767(0x7FFF). If Vcc is 3.3V, this is what I would expect with the voltage per bit being about 50uV/bit.

If, however, the DADM0 is tied to a voltage other than Vcc/2, what can I expect of the differential voltage is greater than Vcc/2. For example, if DADM0 = 0.8V and DADP0 is greater than 2.4V (0.8V + Vcc/2), what can I expect after the conversion? Will it just top out at the maximum of 0x7FFF, or will the result be indeterminant?

Thanks.

[david_diaz]

Hello David,

The differential ADC will measure the voltage difference between two pins, DADPx and DADMx, no matter if one input is different to Vcc/2.

In this case the DADPx is acting as the ‘sign bit’. If DADPx voltage is larger than DADMx, sign bit doesn't be set; otherwise, if DADPx voltage is smaller than DADMx, sign bit is set.

I hope this information will be useful for you. In case you still have questions, please let me know. I will be glad to help.

Have a great day. :smileyhappy:

David