SLUUBY1B December 2020 – April 2022 BQ76942
The BQ76942 device integrates a broad suite of protections for battery management and provides the capability to enable individual protections, as well as to select which protections will result in autonomous control of the FETs. The Settings:Manufacturing:Mfg Status Init[FET_EN] configuration bit determines whether the device is in autonomous control mode (when set) or in FET test mode (when cleared). The FET test mode is primarily for use on a customer production line, to test individual FETs. The autonomous control mode is recommended for field operation, which still allows the host to disable FETs through serial communications or using the CFETOFF and DFETOFF pins, and block their re-enabling by the device until the host allows.
The individual protections can be enabled by setting the related Settings:Protection:Enabled Protections A – C configuration registers. The protections controlled by Settings:Protection:Enabled Protections A are comparator-based, while those in Settings:Protection:Enabled Protections B and C are firmware-based.
Each protection that has been enabled can also be controlled regarding whether it will disable a particular FET or not by setting related configuration bits. The bits in Settings:Protection:CHG FET Protections A – C determine which protections will trigger the CHG FET being disabled, while those in Settings:Protection:DSG FET Protections A – C determine which will trigger the DSG FET being disabled. Note: protections which are configured to disable the CHG FET will also disable the precharge FET when it is enabled. Similarly, protections configured to disable the DSG FET will also disable the predischarge FET when it is enabled.
Most protections involve the device checking for a violation of a particular condition, such as a voltage or current threshold. As soon as a violating condition is detected for an enabled protection, a safety alert is set. Flags showing which safety alerts may be present are available through the 0x02 Safety Alert A, 0x04 Safety Alert B, and 0x06 Safety Alert C commands, and their presence can generate an interrupt to a host processor on the ALERT pin.
Most protections also include a delay, such that if the violating condition persists for some time interval, a safety fault is triggered. Flags showing which safety faults may be present are available through the 0x03 Safety Status A, 0x05 Safety Status B, and 0x07 Safety Status C commands, and their presence can generate an interrupt to a host processor on the ALERT pin.
The format of the safety alert and safety status commands is shown below.
Bit | Name | Description |
7 | SCD | Short Circuit in Discharge safety alert is present |
6 | OCD2 | Overcurrent in Discharge 2 safety alert is present |
5 | OCD1 | Overcurrent in Discharge 1 safety alert is present |
4 | OCC | Overcurrent in Charge safety alert is present |
3 | COV | Cell Overvoltage safety alert is present |
2 | CUV | Cell Undervoltage safety alert is present |
1 | RSVD | Reserved |
0 | RSVD | Reserved |
Bit | Name | Description |
7 | SCD | Short Circuit in Discharge safety fault is present |
6 | OCD2 | Overcurrent in Discharge 2 safety fault is present |
5 | OCD1 | Overcurrent in Discharge 1 safety fault is present |
4 | OCC | Overcurrent in Charge safety fault is present |
3 | COV | Cell Overvoltage safety fault is present |
2 | CUV | Cell Undervoltage safety fault is present |
1 | RSVD | Reserved |
0 | RSVD | Reserved |
Bit | Name | Description |
7 | OTF | FET Overtemperature safety alert is present |
6 | OTINT | Internal Die Overtemperature safety alert is present |
5 | OTD | Overtemperature in Discharge safety alert is present |
4 | OTC | Overtemperature in Charge safety alert is present |
3 | RSVD | Reserved |
2 | UTINT | Internal Die Undertemperature safety alert is present |
1 | UTD | Undertemperature in Discharge safety alert is present |
0 | UTC | Undertemperature in Charge safety alert is present |
Bit | Name | Description |
7 | OTF | FET Overtemperature safety fault is present |
6 | OTINT | Internal Die Overtemperature safety fault is present |
5 | OTD | Overtemperature in Discharge safety fault is present |
4 | OTC | Overtemperature in Charge safety fault is present |
3 | RSVD | Reserved |
2 | UTINT | Internal Die Undertemperature safety fault is present |
1 | UTD | Undertemperature in Discharge safety fault is present |
0 | UTC | Undertemperature in Charge safety fault is present |
Bit | Name | Description |
7 | OCD3 | Overcurrent in Discharge 3 safety alert is present |
6 | SCDL | Latched Short Circuit in Discharge safety alert is present |
5 | OCDL | Latched Overcurrent in Discharge safety alert is present |
4 | COVL | Latched Cell Overvoltage safety alert is present |
3 | PTOS | Precharge timer is suspended due to current below Protections:PTO:Charge Threshold |
2 | RSVD | Reserved |
1 | RSVD | Reserved |
0 | RSVD | Reserved |
Bit | Name | Description |
7 | OCD3 | Overcurrent in Discharge 3 safety fault is present |
6 | SCDL | Latched Short Circuit in Discharge safety fault is present |
5 | OCDL | Latched Overcurrent in Discharge safety fault is present |
4 | COVL | Latched Cell Overvoltage safety fault is present |
3 | RSVD | Reserved |
2 | PTO | Precharge Timeout safety fault is present |
1 | HWDF | Host watchdog safety fault is present |
0 | RSVD | Reserved |