impedance is 52 kohms. Based on my measurements and calculations it is 25
kohms. In my experiment, VP3 is connected through 100kohm resistor to 5V.
Voltage at VP3 pin is 1.0 V, so there is 4V over the 100kohm resistor,
therefore the impedance must be 25kohm. (5V/125k)*25k = 1V. Can you please
check this value ?
The input impedance on the VPX pins is specified as typically 52kOhms in the
datasheet, but no min/max is given there. In practice, the values of the input
impedance can vary from ~22kOhm up to ~70 k Ohms depending on process
variations - so your measurement of 25kOhm is not surprising at all.