SLUUBT5C November 2018 – June 2021 BQ40Z80
The BQ40Z80 device provides overtemperature and undertemperature protections, based on cell temperature measurement and FET temperature measurements. The cell temperature based protections are further divided into a protection-in-charging direction and discharging directions. This section describes in detail each of the protection functions.
For temperature reporting, the device supports a maximum of four external thermistors and one internal temperature sensor. Unused temperature sensors must be disabled by clearing the corresponding flag in Settings:Temperature Enable[TS4][TS3][TS2][TS1][TSInt].
Each of the external thermistors and the internal temperature sensor can be set up individually as a source for cell temperature or FET temperature reporting. Setting the corresponding flag to 1 in Settings:Temperature Mode[TS4 Mode][TS3 Mode][TS2 Mode][TS1 Mode][TSInt Mode] configures that temperature sensor to report for FET temperature. Clearing the corresponding flag sets that temperature sensor to report for cell temperature. The Settings:DA Configuration[FTEMP] enables users to use the maximal (setting the corresponding flag to 0) or the average (setting the corresponding flag to 1) of the source temperature sensors for FET temperature reporting.
The Settings:DA Configuration[CTEMP1][CTEMP0] enables users to define which temperature sensor's output is displayed by the SBS Temperature() command (a setting of 1, 0 allows the temperature sensor with the lowest temperature to be displayed, while a setting of 0, 1 displays an average of all the sensors, and a setting of 0, 0 displays the temperature sensor with the highest temperature). Cell temperature protections will work automatically such that for the under temperature check, only the MIN cell temperature will be used, while for over temperature check only the MAX cell temperature will be used.
The Temperature() command returns the cell temperature measurement. The MAC and extended command DAStatus2() also returns the temperature measurement from the internal temperature sensor, the external thermistors TS1, TS2, TS3, and TS4, and the cell and FET temperatures.
If set, the Settings:SBS Configuration[SMB_CELL_TEMP] bit enables the host to write via the MAC command 0x3008 to the temperature register (this is the register from which the Temperature() command returns a read). On power up, if [SMB_CELL_TEMP] = 1, the temperature register is written to 293 K (that is, 20°C). When this feature is used, the temperature must be written in 0.1 K. Additionally, since the gauge’s TS inputs are not being used, then the TS1 through TS4 settings (in register Temperature Enable) are irrelevant (as are CTEMP1 and CTEMP0). This feature is helpful on PCBs that do not have the area or height to include thermistors, but do have a host that is capable of using its own onboard measurement of cell temperature (as well as bypassing the gauge’s cell temperature inputs, TS1 through TS4, and setting it using an SMBus command).
The cell temperature based overtemperature and undertemperature safety provides protections in charge and discharge conditions. The battery pack is in CHARGE mode when BatteryStatus()[DSG] = 0, where Current() > Chg Current Threshold. The overtemperature and undertemperature in charging protections are active in this mode. BatteryStatus()[DSG] is set to 1 in a non-CHARGE mode condition, which includes RELAX and DISCHARGE modes. The overtemperature and undertemperature in discharge protections are active in these two modes. See Section 8.3 for detailed descriptions of the gas gauge modes.