ZHCSMK4A september 2022 – july 2023 ADS131B26-Q1
PRODUCTION DATA
In addition to the dedicated supply monitors, all supplies (APWR, DPWR, AVDD, IOVDD, and DVDD) can also be measured back internally through ADC2A or ADC2B. Resistor dividers are integrated in the device to attenuate the supply voltages to within the input voltage range of ADC2A and ADC2B. See the Electrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical Characteristics table for the according attenuation factors. Use the SEQ2y_STEPx_CH_P[3:0] bits to configure an ADC2y sequence step for any of the supply voltage measurements.
The supply voltage measurement accuracy depends on two factors:
The large resistor divider values used internally to divide the supply voltages down together with the internal filter capacitor lead to a large RC filter time constant. The input signal therefore needs considerable time to settle when the ADC2y multiplexer selects one of the supply voltage measurements. Increasing the multiplexer delay time provides more time for the input signal to settle after the multiplexer change before ADC2y starts converting. Setting the multiplexer delay time equal to or greater than 256 × tMCLK provides sufficient time for the input signals to settle when measuring the supply voltages.
If increasing the multiplexer delay time is not possible, because the delay time affects all sequence steps equally, configure multiple consecutive sequence steps for the same supply voltage measurement. Then disregard the initial sequence step readings where the conversions are not settled yet.
The input impedance of ADC2y changes with the selected conversion time, see the Electrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical Characteristics table. The impedance of the resistor divider interacts with the input impedance of ADC2y leading to a gain error. Increasing the ADC2y input impedance by increasing the ADC2y conversion time reduces the gain error for the supply voltage measurements.
See Figure 7-32 for details on how the supply voltage measurement accuracy changes with the multiplexer delay time and the ADC2y conversion time.