The maximum impedance is limited by the input voltage range of the ADC and the drive current. With the minimum PGA gain of 10 V/V, the lower drive current of 8uA, and the ADC's input voltage range of 1V, the maximum measureable impedance is 12.5 kOhms. To measure larger impedances, a resistor can be placed in parallel with the measured impedance such that the parallel combination is less than 12.5 kOhms. After measuring the impedance, the larger impedance can be back-calculated.