31.3.3.5.3 Analog Input Circuit

The figure below illustrates the analog input circuit. An analog source connected to an analog input (AINn) is subject to the pin capacitance and input leakage of that pin (represented by I_H and I_L). When the input is selected, the source must also drive the Sample-Hold capacitor (C_IN) through the combined resistance of the input path (represented by R_IN). Refer to the Electrical Characteristics section for details on the input characteristics of the ADC.

Figure 31-2. Analog Input Schematic

If a source with high impedance is used, the sampling time may need to be increased. The required sample time will depend on how long the source needs to charge the C_IN capacitor and can be configured using the Sample Duration (SAMPDUR) bit field in the Control E (ADCn.CTRLE) register.