JAJSN92 December 2022 AFE78101 , AFE88101
PRODUCTION DATA
In addition to the ADC offset, the two external monitoring inputs, and the temperature sensor, the ADC of the AFEx8101 has five other internal inputs to monitor the reference voltage, the power supplies, a static voltage, and the DAC output. These five voltages measurements are part of the self-diagnostic multiplexer (SD0 to SD4) measurements of the ADC, and are reported in the ADC_SD_MUX register at 27h; see also Section 7.6.
Channel 4 (SD0) measures the reference voltage of the device. The ADC measures the reference voltage through a resistor divider (divide by two). Be aware that all ADC measurements are a function of the reference; using SD0 to measure the reference is not revealing as a diagnostic measurement. The data rate for this conversion is 2560 Hz and the range of the ADC is set to VREF.
Channel 5 (SD1) measures the PVDD power supply of the device. The ADC measures the PVDD voltage through a resistor divider (divide by six). The data rate for this conversion is 2560 Hz and the range of the ADC is set to VREF.
Channel 6 (SD2) measures the VDD power supply of the device. When channel 6 is selected, the ADC measures the VDD voltage through a resistor divider (divide by 2). The data rate for this conversion is 2560 Hz and the range of the ADC is set to VREF.
Channel 7 (SD3) is a ZTAT (zero temperature coefficient) voltage. This internal voltage is nominally 0.6 V with a low temperature drift and does not depend on the reference voltage. An ADC measurement of ZTAT voltage can be useful to determine the state of the reference voltage. The data rate for this conversion is 2560 Hz and the range of the ADC is set to VREF.
Channel 8 (SD4) measures the VOUT of the DAC. The ADC measures the VOUT voltage through a resistor divider (divide by two). The data rate for this conversion is 2560 Hz.
The input range for the DAC voltage monitoring input is scaled from either 0-V to 2.5-V or 0-V to 1.25-V, depending on PVDD voltage. As soon as the PVDD voltage exceeds 2.7 V, the input range for the DAC voltage monitoring automatically switches to the 0-V to 2.5-V range. The DAC voltage conversion values are stored in straight-binary format in the ADC registers. The ADC resolution for these channels is computed by Equation 7.