ZHCSH75A September 2017 – December 2017 ADS7142
PRODUCTION DATA.
Figure 39 shows a small-signal equivalent circuit for the analog input pins. The device includes a two-channel analog multiplexer with each input pin having ESD protection diodes to AVDD and GND. The sampling switches are represented by ideal switches SW1 and SW2 in series with resistors Rs1 and Rs2 (typically 150 Ω). The sampling capacitors, Cs1 and Cs2, are typically 15 pF. The multiplexer configuration is set by the CHANNEL_INPUT_CFG register.
During acquisition, switches SW1 and SW2 are closed to allow the input signal to charge the internal sampling capacitors.
During conversion, switches SW1 and SW2 are opened to disconnect the input signal from the sampling capacitors.
The analog input of the device are optimized to be driven by high impedance source (up-to 100 kΩ) in Autonomous Modes or in High Precision Mode mode with low power oscillator. It is recommended to drive the analog input of the device with an external amplifier when in Autonomous Modes or in High Precision Mode mode with High Speed oscillator. Figure 30 and Figure 31 provide the analog input current for CH0 and CH1 of the device.
Figure 40, Figure 41 and Figure 42 provide a simplified circuit for analog input for input configurations described in Two-Channel, Single-Ended Configuration, Single-Channel, Single-Ended Configuration and Single-Channel, Pseudo-Differential Configuration respectively. The analog multiplexer supports following input configurations (set by writing into CHANNEL_INPUT_CFG register).