The BQ76905 includes several measurements and checks for diagnostic purposes. Some of these trigger a protection fault, but they generally do not include an alert phase with programmable delay period. They immediately trigger a fault when they are detected. They are not all autonomously recoverable, but some can be manually recovered using a subcommand sent by the host. For more details on each diagnostic, see the BQ76905 Technical Reference Manual.

VREF1 vs. VREF2 Check—The device performs a regular comparison of the two internal voltage references and can trigger a fault if the result is outside an acceptable range. This is implemented using a measurement of the internal 1.8 V LDO voltage (which is based on VREF2) with the ADC using VREF1 for its reference.

VSS Check—The device also includes a regular measurement of the VSS voltage as part of the measurement loop, comparing the resulting value to the expected value, in order to implement the VSSF Diagnostic Protection.

Stack Check—The device includes a regular measurement of the top-of-stack (TOS) voltage as part of the measurement loop. This measurement can be used by the host to compare with the sum of the individual differential cell voltage measurements, with a significant difference possibly indicating some type of malfunction.

REGOUT Check—The REGOUT LDO generates a flag if an error is detected, such as the regulator is in short circuit current limit. When detected, the device triggers the REGOUT Diagnostic Fault and can disable FETs based on settings.

LFO Integrity Check—The device integrates a special hardware block that monitors if the LFO stops oscillating or drops significantly in frequency versus its expected value. If this is detected, the device immediately transitions into SHUTDOWN mode.

Internal Factory Trim Check—The device includes a check of the digital trim and setting information within the device at initial power up or after any full reset. If an error is detected during this check, the device immediately transitions to SHUTDOWN mode.

Hardware Overtemperature Detector—The device integrates a hardware overtemperature detection circuit, which determines when the die temperature passes an excessive temperature of approximately 120°C. If this detector triggers, the device automatically begins the sequence to enter SHUTDOWN, based on the configuration setting.