SLUUCP8 June 2024 BQ41Z50
The BQ41Z50 device provides overtemperature and undertemperature protections, based on cell and FET temperature measurements. The cell temperature-based protections are further divided into CHARGE and DISCHARGE conditions. This section describes in detail each of the protection functions.
The device supports four external thermistors and one internal temperature sensor for measuring temperature. Unused temperature sensors must be disabled by clearing the corresponding flag in Settings:Temperature Enable[USER_TS][TS4][TS3][TS2][TS1][TSInt].
Each of the temperature sensors can be used as a source for cell or FET temperature measurement. Setting the corresponding flag in Settings:Temperature Mode[USER_TS Mode][TS4 Mode][TS3 Mode][TS2 Mode][TS1 Mode][TSInt Mode] configures the sensor to measure FET temperature. Clearing the corresponding flag configures the sensor to measure cell temperature.
The average temperature among the sensors set for FET measurement is used when Settings:DA Configuration[FTEMP] is set. The maximum temperature is used when [FTEMP] is cleared.
Under cell temperature protections use the minimum cell temperature sensor. Over cell temperature protections use the maximum cell temperature sensor.
The Temperature() command returns the cell temperature measurement. Setting Settings:DA Configuration[CTEMP1][CTEMP0] to 1, 1 uses the smart temperature sensor. Setting Settings:DA Configuration[CTEMP1][CTEMP0] to 1, 0 uses the lowest cell temperature sensor. Setting [CTEMP1][CTEMP0] to 0, 1 uses the average of the sensors. A setting of 0, 0 uses the maximum cell temperature sensor.
Smart temperature sensor scheme [CTEMP1][CTEMP0] = 1, 1 determine the cell temperature as:
ManufacturerBlockAccess() command DAStatus2() returns all the temperature measurements.
The Settings:Temperature Mode[USER_TS] bit enables the host to write the user temperature with the MAC command WriteTemp(). When this feature is used, the temperature must be written in 0.1°K. 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. If [USER_TS] = 1, like other [TS4 Mode][TS3 Mode][TS2 Mode][TS1 Mode] options cell or FET temperature is selected as per Settings:DA Configuration[CTEMP1][CTEMP0] settings. To enable writing the temperature with MAC command WriteTemp(), first a two-word override MAC sequence is required. The two-word key is programmable using ManufacturerAccess() 0x0035 Security Keys. Both keys must be sent within 4 seconds of each other. Once the correct two-word MAC sequence is received, ManufacturerAccess() 0x3008 WriteTemp() can be used.
The cell-based overtemperature and undertemperature safety provides protections in CHARGE and DISCHARGE conditions. The battery pack is in CHARGE mode when Current() > Chg Current Threshold and BatteryStatus()[DSG] = 0. The overtemperature and undertemperature in CHARGE 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 6.3 for detailed descriptions of the gas gauge modes.