SLUUCA6 October 2021 BQ27Z746
Firmware cannot override any hardware based protection. The firmware protections are used to signal impending hardware protection. This can allow a host system to respond to conditions before hardware protection opens a FET. Some of the firmware protection can be programmed to open a FET. Every firmware protection has two associated signals. When a threshold violation is detected the associated status bit is set. Each threshold has an associated timer. If the timer expires an associated status bit is set. If the status bit has an active associated FET control action, that action will be taken when the status bit is set. All firmware based protections have an associated recovery threshold.
When the protection is triggered, charging and/or discharging is disabled. This is indicated by the OperationStatus()[XCHG] = 1 when charging is disabled (the CHG FET is turned OFF), and/or the OperationStatus()[XDSG] = 1 when discharging is disabled (DSG FET is turned OFF). Once the protection is recovered, charging and discharging resume. All firmware-based protections can be enabled or disabled under Settings:Enabled Protections A, Settings:Enabled Protections B, Settings:Enabled Protections C, and Settings:Enabled Protections D. All hardware-based protections are either enabled or disabled, which is based on the configuration image stored in secure memory.
To protect the DSG FET body diode, the DSG FET will always be closed when Current() ≥ Chg Current Threshold, including when OperationStatus()[XDSG] = 1. Likewise, to protect the CHG FET body diode, the CHG FET will always be closed when Current() ≤ (–)Dsg Current Threshold, including when OperationStatus()[XCHG] = 1. Setting FET Options[IWAKE_FET] = 1 configures the device to protect the body diode of the CHG FET during low power modes such as SLEEP and SHIP when the hardware-based IWAKE threshold is surpassed. This is because the IWAKE threshold can only be configured to detect discharge current.
When the protections are triggered, BatteryStatus()[TCA][TDA][FD][OCA][OTA] is set according to the type of safety protections. Section 12.10 provides a summary of the various alarms flags' set conditions.
Delay settings with 1-s granularity can have an average trigger delay equal to the delay setting plus 1.8 s.