SNIU028D February 2016 – September 2020 UCD3138 , UCD3138064 , UCD3138064A , UCD3138128 , UCD3138A , UCD3138A64
Except for the external and internal RC values, the initial charge V0 on the S/H capacitor also affects the time needed to charge the S/H capacitor to the desired voltage level. If the source impedance is high, there is a large time constant for the S/H capacitor to discharge. Thus the voltage remaining on the S/H capacitor will affect the next conversion.
Generally, for UCD3138, several ADC channels are used for different monitoring purposes. When designing the ADC input circuit, it is highly recommended to avoid high impedance node, because high impedance node may result in extra impedance roll-offs due to crosstalk.