SBAS925A August 2018 – November 2018 ADS1119
The ADS1119 can measure single-ended signals ranging from AGND to VREF / Gain. In order to monitor voltages up to 2 V, the device is configured to use the internal 2.048-V reference and gain = 1.
Equation 6 details the relationship between output codes of the ADS1119 and the input voltage on AIN3.
An external voltage reference must be provided on the external reference inputs of the device in case larger voltages than 2.048 V are to be monitored. The device can measure input signals up to the positive analog supply voltage in case AVDD is used as the positive reference input (REFP) and AGND as the negative reference input (REFN). However the ADS1119 cannot monitor its own supply voltage in that case. As described in Equation 6, when using VAIN3 = AVDD and VREF = AVDD, the device will always output a positive full-scale code irrespective of the value of AVDD. To monitor the supply of the ADC, use a resistor divider instead to divide the supply voltage down to below 2.048 V and measure the voltage using the internal reference.
The input-referred peak-to-peak noise of the ADC is ideally a factor smaller than the required measurement accuracy of ±0.5 mV. At 90 SPS using gain = 1 the ADS1119 offers an input-referred noise of 62.5 µVPP, which meets this requirement.