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.
11.2 Primary Protections
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. See the
BQ76942 Technical Reference Manual
for detailed descriptions of each protection function.
The primary protection features include:
• Cell Undervoltage Protection
• Cell Overvoltage Protection
• Cell Overvoltage Latch Protection
• Overcurrent in Charge Protection
• Overcurrent in Discharge Protection (Three Tiers)
• Overcurrent in Discharge Latch Protection
• Short Circuit in Discharge Protection
• Short Circuit in Discharge Latch Protection
• Undertemperature in Charge Protection
• Undertemperature in Discharge Protection
• Internal Undertemperature Protection
• Overtemperature in Charge Protection
• Overtemperature in Discharge Protection
• Internal Overtemperature Protection
• FET Overtemperature Protection
• Precharge Timeout Protection
• Host Watchdog Fault Protection
11.3 Secondary Protections
The BQ76942 device integrates a suite of secondary protection checks on battery operation and status that
can trigger a permanent fail (PF) if conditions are considered so serious that the pack should be permanently
disabled. The various PF checks can be enabled individually based on configuration settings, along with
associated thresholds and delays for most checks. When a permanent fail has occurred, the BQ76942 device
can be configured to either simply provide a flag, or 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 also can
monitor if a separate secondary protector IC has attempted to blow the fuse.
Since the device stores permanent fail status in RAM, that status would be lost when the device resets.
To mitigate this, the device can write permanent fail status to OTP based on configuration setting. OTP
programming may be delayed in low-voltage and high-temperature conditions until OTP programming can
reliably be accomplished.
SLUSE14B – DECEMBER 2020 – REVISED DECEMBER 2021
Copyright © 2021 Texas Instruments Incorporated
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