SLUUCF2 User guide

SLUUCF2C January 2021 – May 2022 BQ769142

5.2.4 Cell Overvoltage Protection

The BQ769142 device integrates Cell Overvoltage Protection (COV), monitoring the voltage of every cell using a comparator-based circuit, and triggering a COV alert or fault when a cell voltage exceeds the COV threshold. The COV threshold is programmable from 1.012 V to 5.566 V in 50.6 mV steps and is set by the Protections:COV:Threshold configuration register. The COV protection is enabled using the Settings:Protection:Enabled Protections A:[COV] configuration bit.

The COV circuitry triggers an alert signal when an overvoltage event is first detected, then will trigger a fault after a programmable detection delay, COV_DLY, which can be set from 10 ms to 6762 ms in units of 3.3 ms, with the actual delay being 3.3 ms × (2 + setting). The setting 0x0 disables the protection. The delay is set by the Protections:COV:Delay configuration register.

When a COV fault is triggered, it will recover if the maximum cell voltage drops below the COV threshold by a COV_HYS hysteresis level, which is programmable from 100 mV to 1 V in steps of 50 mV, for Protections:Recovery:Time. The COV_HYS hysteresis level is set by the Protections:COV:Recovery Hysteresis configuration register.

When an COV fault is triggered, the device will turn off the CHG FET if configured for autonomous FET control based on setting in Settings:Protection:CHG FET Protections A[COV] (the DSG FET remains enabled if already enabled). The device will recover (if configured for autonomous FET control) based on all cell voltages being below COV threshold – COV_HYS for Protections:Recovery:Time.

The BQ769142 device also includes a Cell Overvoltage Latch (COVL) protection, which can create a fault if multiple COV failures occur within a programmable time window. Whenever a COV fault is triggered, the COVL latch counter is incremented. After the device recovers, it will decrement the COVL counter after a programmable recovery time window (given by Protections:COVL:Counter Dec Delay) if no further COV faults are detected. If the COVL counter reaches a programmable latch limit (given by Protections:COVL:Latch Limit), it will trigger a COVL fault.

The COVL protection recovers after a programmable delay given by Protections:COVL:Recovery Time, but it is important that Protections:COVL:Counter Dec Delay be set shorter than Protections:COVL:Recovery Time, otherwise COVL would immediately trip again after recovery, since the COVL counter would not have decremented yet. The COVL protection is enabled using the Settings:Protection:Enabled Protections C:[COVL] configuration bit. Table 6-10 provides further details.

Note: Timing on COV changes while cell balancing is active, as described in Cell Balancing Loop Slow-down Setting.

Table 5-10 Overvoltage Protection Operation

Status	Condition	Action
Normal	Max cell voltage < *Protections:COV:Threshold*	Safety Alert A()[COV] = 0 Decrement COVL counter by one after each *Protections:COVL:Counter Dec Delay* period if COVL counter > 0
Alert	Max cell voltage ≥ *Protections:COV:Threshold*	Safety Alert A()[COV] = 1
Trip	Max cell voltage ≥ *Protections:COV:Threshold* for *Protections:COV:Delay* duration	Safety Alert A()[COV] = 0 Safety Status A()[COV] = 1 Alarm Raw Status()[XCHG] = 1 if autonomous FET control is enabled Increment COVL counter
Recovery	Safety Status A()[COV] = 1 and Max cell voltage < *Protections:COV:Threshold–Protections:COV:Recovery Hysteresis* for *Protections:Recovery:Time*	Safety Status A()[COV] = 0 Alarm Raw Status()[XCHG] = 0 if autonomous FET control is enabled
Latch Alert	COVL counter > 0	Safety Alert C()[COVL] = 1
Latch Trip	COVL counter ≥ *Protections:COVL:Latch Limit*	Safety Status C()[COVL] = 1 Safety Alert C()[COVL] = 0 Alarm Raw Status()[XCHG] = 1 if autonomous FET control is enabled
Latch Reset	SafetyStatus()[COVL] = 1 for *Protections:COVL:Recovery Time* duration	Safety Status C()[COVL] = 0 Alarm Raw Status()[XCHG] = 0 if Safety Status A()[COV] = 0 and autonomous FET control is enabled

When a COV fault is triggered, a snapshot of all cell voltages is captured and can be accessed through the 0x0081 COV_SNAPSHOT() subcommand, which has the format shown in Table 6-11.

Table 5-11 0x0081 COV_SNAPSHOT() Subcommand Format

Subcommand Address	Bytes Within Block	Name	Unit
0x0081	0–1	Cell 1 Voltage at COV	mV
	2–3	Cell 2 Voltage at COV	mv
	4–5	Cell 3 Voltage at COV	mV
	6–7	Cell 4 Voltage at COV	mV
	8–9	Cell 5 Voltage at COV	mV
	10–11	Cell 6 Voltage at COV	mV
	12–13	Cell 7 Voltage at COV	mV
	14–15	Cell 8 Voltage at COV	mV
	16–17	Cell 9 Voltage at COV	mV
	18–19	Cell 10 Voltage at COV	mV
	20–21	Cell 11 Voltage at COV	mV
	22–23	Cell 12 Voltage at COV	mV
	24–25	Reserved	‒
	26–27	Cell 13 Voltage at COV	mV
	28–29	Reserved	‒
	30–31	Cell 14 Voltage at COV	mV