JAJSEG5A January 2018 – October 2018 ADS112U04
Figure 45 shows the flexible input multiplexer of the device. Either four single-ended signals, two differential signals, or a combination of two single-ended signals and one differential signal can be measured. The multiplexer is configured by four bits (MUX[3:0]) in the configuration register. When single-ended signals are measured, the negative ADC input (AINN) is internally connected to AVSS by a switch within the multiplexer. For system-monitoring purposes, the analog supply [(AVDD – AVSS) / 4] or the currently selected external reference voltage [(VREFP – VREFN) / 4] can be selected as inputs to the ADC. The multiplexer also offers the possibility to route any of the two programmable current sources to any analog input (AINx) or to the dedicated reference pins (REFP, REFN).
Electrostatic discharge (ESD) diodes to AVDD and AVSS protect the inputs. The absolute voltage on any input must stay within the range provided by Equation 3 to prevent the ESD diodes from turning on:
If the voltages on the input pins have any potential to violate these conditions, external Schottky clamp diodes or series resistors may be required to limit the input current to safe values (see the Absolute Maximum Ratings table). Overdriving an unused input on the device can affect conversions taking place on other input pins.