8.3.6.3 CB_DONE, OVUV, and OTUT Built-In Self Test (BIST)

The CBDONE, OVUV and OTUT comparators contain a BIST function for diagnostic purposes. When enabled, the BIST tests each of the individual comparators. The BIST is enabled for the OVUV comparators using the DIAG_CTRL1[OVUV_MODE] and DIAG_CTRL1[OTUT_MODE] bits. There are three options: Perform the round-robin with BIST enabled, perform the round robin with BIST disabled, and single channel mode, where the comparators remain fixed on a selected input. When the BIST is enabled (DIAG_CTRL1[OVUV_MODE] = 0b00, DIAG_CTRL1[OTUT_MODE] = 0b00), the BIST is run on every other round robin cycle. This ensures that the BIST is run within two times t_CYCLE.

The comparator is tested by comparing a diagnostic DAC voltage (generated from REF2) to the selected threshold. The diagnostic DAC voltage is switched from 2 LSB below the threshold to 2 LSB above the threshold and the output of the comparator is checked to ensure it switches. If the comparator does not switch, the corresponding bit is set as follow:

• For OV comparator: OVUV_BIST_FAULT[OVCOMP]
• For UV comparator: OVUV_BIST_FAULT[UVCOMP]
• For OT comparator: OTUT_BIST_FAULT[OTCOMP]
• For UT comparator: OTUT_BIST_FAULT[UTCOMP].

The VCBDONE comparator BIST follows the same process and is enabled by the DIAG_CTRL1[OVUV_MODE] bits. If the BIST fails during the VCBDONE comparator BIST test, the SYS_FAULT3[CB_VDONE] bit is set. All signals during BIST are deglitched by t_BISTDG.