SLUUBY1B December 2020 – April 2022 BQ76942
The BQ76942 device supports both a series configuration and a parallel configuration for the protection FETs in the system, as well as a system which does not use one or both FETs. If the device FET drivers are not used at all, the charge pump should be disabled by clearing Settings:FET:Chg Pump Control[CPEN] and clearing Settings:FET:FET Options[FET_CTRL_EN]. The Settings:FET:FET Options[SFET] configuration bit should be set when FETs are used in a series configuration, and should be cleared if FETs are used in a parallel configuration. If the system will only use a single FET (such as a CHG FET with no DSG FET), the device can be configured for parallel configuration with the DFETF Permanent Fail disabled.
When a series FET configuration is used, the BQ76942 device provides body diode protection for the case when one FET is off and one FET is on. This situation might occur in SLEEP mode (when the DSG FET is on and the CHG FET may be off) or in a cell undervoltage fault condition, when the DSG FET may be off, but the CHG FET may still be on.
If the CHG FET is off, the DSG or PDSG FET is on, and a discharge current greater in magnitude thanSettings:Protection:Body Diode Threshold (that is, a significant discharging current) is detected, the device will turn on the CHG FET, to avoid current flowing through the CHG FET body diode and damaging the FET. When the current rises above the threshold (that is, less discharge current flowing), the CHG FET will be turned off again if the reasons for its turn-off are still present. |
If the DSG FET is off, the CHG or PCHG FET is on, and a current in excess of +Settings:Protection:Body Diode Threshold (that is, a significant charging current) is detected, the device will turn on the DSG FET, to avoid current flowing through the DSG FET body diode and damaging the FET. When the current falls below the threshold (that is, less charging current flowing), the DSG FET will be turned off again if the reasons for its turn-off are still present. |
When a parallel configuration is used (Settings:FET:FET Options[SFET] = 0), the body diode protection is disabled.