SLUUCA6 October 2021 BQ27Z746
To minimize power consumption and avoid draining the battery, the device can be configured to shut down at a programmable cell voltage threshold, Shutdown Voltage. If Shutdown Voltage is configured above the cell undervoltage thresholds, the delay to enter SHUTDOWN may be longer than Shutdown Time, because the voltage on the PACK terminal takes time to drain (assuming a charger is not attached) once the DSG FET turns off. The time to drain the PACK terminal depends on the load attached.
In a test environment, it is possible to quickly drop the cell voltage below Shutdown Voltage. Even if Shutdown Voltage is configured below the cell undervoltage thresholds, the PACK terminal may take extra time to drain, especially if PACK+ is floating. However, this should not be a concern with a system load attached with sufficient voltage margin between the Shutdown Voltage and the DSG FET turning off.
Status | Condition | Action |
---|---|---|
Enable | Cell voltage < Shutdown Voltage | OperationStatus()[SDV] = 1 |
Trip | Cell voltage continuous < Shutdown Voltage for Shutdown Time | Turn DSG FET off |
Shutdown | Voltage at PACK terminal < Charger Present Threshold AND Current() ≤ 0 AND ENAB pin is high | Send device into SHUTDOWN mode |
Exit | Voltage at PACK terminal > VSTARTUP OR ENAB pin pulled low OR Cell voltage > Shutdown Voltage if not in SHUTDOWN mode | OperationStatus()[SDV] = 0 Return to NORMAL mode |
The device goes through a full reset when exiting from SHUTDOWN mode, which means the device reinitializes. On power up, the gauge checks certain special memory locations. If the memory checksum is incorrect, or if the watchdog was triggered, the gauge does a full reset.
If the memory checksum is good (for example, in the case of a short power glitch), the gauge does a partial reset. The initialization is faster in a partial reset, and certain memory data is not reinitialized (for example, all SBS registers, last ADC and CC readings, safety alerts, and statuses, and so on) and so a partial reset is usually transparent to the host. After a partial reset, the FETs remain off until the hardware-based cell undervoltage protection, HCUV, is able to complete detection. Once HCUV detection finishes, the FETs turn on or remain off based on this result and the other restored safety statuses.
The configuration options for SHUTDOWN are in the following data flash.
Class | Subclass | Name | Type | Min | Max | Default | Unit | Description |
---|---|---|---|---|---|---|---|---|
Power | Shutdown | Shutdown Voltage | I2 | 0 | 32767 | 2150 | mV | Cell based shutdown voltage trip threshold |
Power | Shutdown | Shutdown Time | U2 | 0 | 255 | 10 | s | Cell based shutdown voltage trip delay |
Power | Shutdown | Charger Present Threshold | I2 | 0 | 32767 | 100 | mV | PACK terminal voltage threshold |