11 Primary and Secondary Protection Subsystems
11.1 Protections Overview
An extensive protection subsystem is integrated within BQ769142, 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 which 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 which is driven onto the NFET
gates based on 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 BQ769142 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 has occurred, the BQ769142 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.
11.2 Primary Protections
The BQ769142 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
BQ769142 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
SLUSE91A – SEPTEMBER 2020 – REVISED FEBRUARY 2021
40
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