Figure 7-2 shows an equivalent circuit for one of the input channels of the ADC128S102-SEP. Diodes D1 and D2 provide ESD protection for the analog inputs. The operating range for the analog inputs is 0 V to V_A. Going beyond this range causes the ESD diodes to conduct and results in erratic operation.

Capacitor C1 in Figure 7-2 has a typical value of 3 pF and is mainly the package pin capacitance. Resistor R1 is the ON-resistance of the multiplexer and track-and-hold switch and is typically 500 Ω. Capacitor C2 is the ADC128S102-SEP sampling capacitor, and is typically 30 pF. The ADC128S102-SEP delivers best performance when driven by a low-impedance source (less than 100 Ω). This source is especially important when using the ADC128S102-SEP to sample dynamic signals. Also important when sampling dynamic signals is a band-pass or low-pass filter, which reduces harmonics and noise in the input. These filters are often referred to as antialiasing filters.

Figure 7-2 Equivalent Input Circuit