After exiting power down mode the conversion result is incorrect?
There are timing specifications to adhere to when exiting power down mode. The
internal circuitry in the AD7091R takes 100us to power up from power down mode.
This is the minimum time that must be maintained between exiting power down
mode and starting the next conversion. Additionally if the on-chip reference is
used it should be ensured that the external reference capacitor is charged to
the correct potential to obtain a correct result. The time to recharge the
reference capacitor is dependent on the charge remaining in the reference
capacitor when the AD7091R exits power down mode.