One slot, the AUX MUX output slot, is assigned in the AUX ADC round robin cycle for the AUX channels (differential AUXn–1 – AUXn, where n = 1 to 4) measurement because these channels are multiplexed to a single input to the AUX ADC multiplexer. For a single AUX channel measurement, it takes multiple round robin cycles because the device has to wait for the AAF settling time as well.

Because of the need to wait for the AAF to settle, the AUX ADC would only measure AUX channels that are active and are selected by the MCU; inactive or unselected channels are skipped.

MCU can control which AUX channels to be measured through the AUX ADC. The ADC_CTRL2[AUX_IN_SEL4:0] gives the options to run through all the active AUX channels or to lock to a single AUX channels. Figure 8-5 shows the example of how the AUX slot is implemented with different [AUX_IN_SEL4:0] setting.

It is recommend to run AUX ADC in continuous mode and all AUX ADC to measure through all the AUX channels once. This enables the device to reduce the common mode error in AUX ADC measurement. MCU shall perform this procedure before running ADC comparison related diagnostic or locking to a single AUX channel measurement.

There is no post-ADC LPF in the AUX ADC path. When the AUX ADC measurements are used during diagnostics, the AUX channel measurements are compared against the Main ADC prefiltered measurements.

The device makes the AUX channel measurement available to read only when the [AUX_IN_SEL4:0] bits are set to lock on a single AUX channel. The measurement is reported in the AUX_HI (high-byte) and AUX_LO (low-byte) registers. The result registers will be updated after the AAF settling time is passed. When cycling through AUX inputs (not in AUX lock mode) , data from round robin cycles 5 through 16 should be disregarded.

Figure 8-7 AUX MUX Output Slot with Different [AUX_IN_SEL4:0] Setting