BQ76PL455APFCT datasheet(38/125 Pages) TI1

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bq76PL455A

SLUSCL0A – SEPTEMBER 2016 – REVISED OCTOBER 2016

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7.3.12.4.1

Special Considerations in Unlatched Fault Mode

In unlatched mode, when the FAULT_2UV and FAULT_2OV registers sense and record secondary protector

(window comparator) faults and one or more other analog die faults (that is, VP_FAULT, VDIG_FAULT, or

VM_FAULT) are present, none of the mentioned faults will clear until all have been cleared, even if the cause of

the fault has gone away. That is, they may appear latched until all these faults are clear.

If these faults (FAULT_SYS[VP_FAULT, VP_CLAMP, VM_FAULT, or VDIG_FAULT]) are present, it is

reasonable to assume that the comparators may not be functioning properly and/or may have stopped reporting

a fault because they stopped functioning rather than the fault condition having gone away.

7.3.12.5 Fault Status and Fault Reset

The following registers can read or reset the fault status individually or in groups:

•

STATUS—Sum of all faults plus stack fault conditions are in this register, some fault information bits are reset

here. This register is at the top of the fault hierarchy.

•

FAULT_SUM—Groups of faults are summarized by single flags in this register and may be either read or

reset here. This is level 2 of the fault hierarchy.

•

FAULT_UV—Undervoltage VSENSE ADC limit exceeded. This is level 3 of the fault hierarchy.

•

FAULT_OV—Overvoltage VSENSE ADC limit exceeded. This is level 3 of the fault hierarchy.

•

FAULT_AUX—Programmable AUX threshold in AUXn_UV or AUXn_OV exceeded. This is level 3 of the fault

hierarchy.

•

FAULT_2UV—Undervoltage VSENSE secondary protection comparator limit exceeded. This is level 3 of the

fault hierarchy.

•

FAULT_2OV—Overvoltage VSENSE secondary protection comparator limit exceeded. This is level 3 of the

fault hierarchy.

•

FAULT_SYS—System level faults: power supplies, over temperature, communications timeout, and reset.

This is level 3 of the fault hierarchy.

•

FAULT_GPI—GPIO (programmable) logic input level triggered a fault. This is level 3 of the fault hierarchy.

•

FAULT_COM—Communication faults. This is level 3 of the fault hierarchy.

•

FAULT_DEV—Device faults. This is level 3 of the fault hierarchy.

7.3.12.6 Checksum Faults

To discover changes to registers, the bq76PL455A constantly runs a background check on their contents by

computing a checksum and comparing it to a stored value. The bq76PL455A detects changes approximately

every two microseconds. The changes can be intentional (that is, a change written by the microcontroller),

unintentional (due to an unexpected device or system fault), or, in some cases, the result of an automated

operation (expiration of the balancing timer). The test runs against the registers in both a TI space and USER

space. This includes most registers with changes that come from the microcontroller; consult Register Summary

for an exact list of included locations.

The CSUM_RSLT register holds the currently computed checksum value. It compares this value against the

stored checksum value in register CSUM. To update the stored value, read the current value in CSUM_RSLT

and write it back to the CSUM register or compute the value as shown in Computing User Checksum. A

checksum saves to CSUM in EEPROM by setting MAGIC1 and MAGIC2 appropriately, then setting

DEV_CTRL[WRITE_EEPROM]. The appropriate values for MAGIC1 and MAGIC2 definitions are in the Register

Details section of this document in the bit description field for the WRITE_EEPROM bit.

When CSUM and CSUM_RSLT do not match, the FAULT_DEV[USER_CKSUM_ERR] flag will be set until the

condition is corrected. This fault flag is unlatched and will self-clear when a mismatch no longer occurs.

Continuous monitoring of the TI EEPROM space occurs in a similar fashion, concurrently with the monitoring of

the USER space. If a register change is detected, the FAULT_DEV[FACT_CKSUM_ERR] flag is set. If this ever

occurs, the user firmware should perform a soft RESET of the part. This fault flag is not self-clearing. Write a 1 to

the bit to clear it. If a soft reset does not correct the issue, do not use the device.

BQ76PL455APFCT Datasheet(PDF) 38 Page - Texas Instruments

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