ZHCSMR2B December 2020 – December 2021 BQ76942
In rare cases, an invalid Cell 1 Voltage() reading has been observed to occur in some devices taken during SLEEP mode.
While the device is in SLEEP mode, each result obtained from reading the Cell 1 Voltage() must be validated before it can be considered valid. During SLEEP mode, current is below programmable thresholds, so the pack is typically not being charged or discharged with any significant level of current. Thus, the cell voltages will generally not be changing significantly.
In order to determine if a measurement of Cell 1 Voltage() taken during SLEEP mode is valid, it is necessary to compare each measurement to measurements taken before and after the particular measurement. It is important that these three readings represent three separate measurements for the Cell 1 Voltage(). If the reading is significantly different from the separate readings taken before and after, then that reading is considered invalid and should be discarded.
In order to ensure the three measurements read from the device are truly separate measurements, the host can read the measurements at intervals exceeding Power:Sleep:Voltage Time while the device is in SLEEP mode. This is necessary to avoid the host reading an existing measurement multiple times, before a new measurement has been taken and is available for readout.
An invalid Cell 1 Voltage() reading may result in an SUV PF Alert being set but does not result in an SUV PF status fault if the SUV Delay is set to 1 second or longer. It also does not trigger a Cell Undervoltage (CUV) Protection alert or status fault, since this protection uses a comparator for its detection. If a reading reported by Cell 1 Voltage() is below the Protections:CUV:Threshold level and the CUV protection is enabled, but the CUV Alert is not triggered, this also can be used as an indication the reading is invalid.
This validation process is necessary to ensure that valid Cell 1 Voltage() results are measured.