SLUUCJ0 November 2023 BQ76907
The BQ76907 device integrates a regular measurement of the VSS voltage as part of the measurement loop, comparing the resulting value to the expected value, to implement the VSS Measurement Diagnostic Protection. If the ADC mux were to malfunction and remain fixed on one particular input, whether that being a cell voltage input, a thermistor, or a diagnostic measurement, this measurement of VSS helps ensure this condition is detected. When detected, the device triggers the VSS Diagnostic Protection Fault and sets 0x03 Safety Status B()[VSS], if enabled, and the device can disable FETs based on Settings:Protection:Both FET Protections B[VSS]. The fault can be recovered by the host sending the 0x009B PROT_RECOVERY()[DIAGREC] subcommand. The expected 16-bit measurement of VSS in 16-bit codes is 0. The diagnostic protection alert is triggered whenever the 16-bit measurement result is beyond ±1625, which is approximately 99 mV / VREF1 × 3 / 5 × 32767. The diagnostic protection status fault is triggered when this occurs for two consecutive VSS measurements.