SLUUCH2 March 2021 BQ40Z50-R2
The system can signal the gas gauge via the PRES pin to open the CFET and DFET, disconnecting the battery power to the host. This feature is only enabled for an embedded pack configuration (that is, [NR] = 1). For a removable battery pack configuration (that is, [NR] = 0), the original PRES pin function remains as a system-present detection. The internal pullup of the PRES pin is enabled for this feature. Entry to the SYSTEM DISCONNECT mode occurs when the gas gauge detects a high-to-low transition of the PRES pin (PRES pin debounce is used). The gauge opens the CFET and DFET in SYSTEM DISCONNECT mode. The OperationStatus()[DISCONN] = 1.
Because the system is shut down in this mode, the gas gauge enters SLEEP mode after a bus timeout. Regardless if the [SLEEPCHG] flag sets, the CFET and DFET will remain off in the SYSTEM DISCONNECT mode.
The PRES pin state is sampled in 250-ms intervals. A “low” is detected by receiving SYS_PRES Delay consecutive low samples. The debounce time ranges from SYS_PRES Delay –1 samples (if the pin state is changed just before a sample is taken) to SYS_PRES Delay samples (if the pin state is changed just after a sample is taken). It exits from the SYSTEM DISCONNECT mode when:
The gauge then returns to NORMAL mode and closes the CFET and DFET.