SLUSE14A December 2020 – February 2021 BQ76942
An extensive protection subsystem is integrated within the BQ76942 device, which can monitor a variety of parameters, initiate protective actions, and autonomously recover based on conditions. The device also includes a wide range of flexibility, such that the device can be configured to monitor and initiate protective action, but with recovery controlled by the host processor, or such that the device only monitors and alerts the host processor whenever conditions warrant protective action, but with action and recovery fully controlled by the host processor.
The primary protection subsystem includes a suite of individual protections that can be individually enabled and configured, including cell undervoltage and overvoltage, overcurrent in charge, three separate overcurrent in discharge protections, short circuit current in discharge, cell overtemperature and undertemperature in charge and discharge, FET overtemperature, a host processor communication watchdog timeout, and PRECHARGE mode timeout. The cell undervoltage and overvoltage, overcurrent in charge, overcurrent in discharge 1 and 2, and short circuit in discharge protections are based on comparator thresholds, while the remaining protections (such as those involving temperature, host watchdog, and precharging) are based on firmware on the internal controller.
The device integrates NFET drivers for high-side CHG and DSG protection FETs, which can be configured in a series or parallel configuration. An integrated charge pump generates a voltage that is driven onto the NFET gates based on a host command or the on-chip protection subsystem settings. Support is also included for high-side PFETs used to implement a precharge and predischarge functionality.
The secondary protection suite within the BQ76942 device can react to more serious faults and take action to permanently disable the pack by initiating a Permanent Fail (PF). The secondary safety provides protection against safety cell undervoltage and overvoltage, safety overcurrent in charge and discharge, safety overtemperature for cells and FETs, excessive cell voltage imbalance, internal memory faults, and internal diagnostic failures.
When a Permanent Fail occurs, the BQ76942 device can be configured either to simply provide a flag, to indefinitely disable the protection FETs, or to assert the FUSE pin to permanently disable the pack. The FUSE pin can be used to blow an in-line fuse and can monitor if a separate secondary protector IC has attempted to blow the fuse.