The ADS124S0x incorporates two integrated, matched current sources (IDAC1, IDAC2). The current sources provide excitation current to resistive temperature devices (RTDs), thermistors, diodes, and other resistive sensors that require constant current biasing. The current sources are programmable to output values between 10 μA to 2000 μA using the IMAG[3:0] bits in the excitation current register 1 (06h). Each current source can be connected to any of the analog inputs AINx as well as the REFP1 and REFN1 inputs for the ADS124S06. Both current sources can also be connected to the same pin. The routing of the IDACs is configured by the I1MUX[3:0] and I2MUX[3:0] bits in the excitation current register 2 (07h). In three-wire RTD applications, the matched current sources can be used to cancel errors caused by sensor lead resistance (see the Typical Application section for more details). Figure 75 details the IDAC connection through the input multiplexer.
The internal reference must be enabled for IDAC operation. As a current source, the IDAC requires voltage headroom to the positive supply to operate. This voltage headroom is the compliance voltage. When driving resistive sensors and biasing resistors, take care not to exceed the compliance voltage of the IDACs, otherwise the specified accuracy of the IDAC current may not be met. For IDAC compliance voltage specifications, see the Electrical Characteristics table.