Hello,
If I were to set A_SYS_CFG to 0x60 which enables the external reference but then don't connect an external reference, what voltage would I expect to see on REFP?
Thanks,
Michael
Michael,
If there's no input on the external reference, then I believe this is an indeterminate voltage. Basically, this is how the reference in the device is set up:
The reference input is gained up by the op-amp and the output drives REFP. However if you look the alternate setting of the internal reference it uses the same opamp for the reference input shown here:
At the (+) input of the opamp, there's an input mux that's used for selecting the reference input. The problems is that the + input could be ballasted by the charge in the cap or there could be some leakage into that node that pulls it to positive or negative supply. This could also change with temperature depending on the amount of leakage.
I don't think that you could determine a specific voltage at the output REFP that's consistent, unless a leakage current at the opamp caused the output to rail.
Joseph Wu
