SLUUCF2 User guide

5.2.5 Cell Undervoltage Protection

The BQ769142 device integrates Cell Undervoltage Protection (CUV), monitoring the voltage of every cell using a comparator-based circuit, and triggering a CUV alert or fault when a cell voltage falls below the CUV threshold. The CUV threshold is programmable from 1.012 V to 4.048 V in 50.6 mV steps and is set by the Protections:CUV:Threshold configuration register. The CUV protection is enabled using the Settings:Protection:Enabled Protections A:[CUV] configuration bit.

The CUV circuitry triggers an alert signal when an undervoltage event is first detected, then triggers a fault after a programmable detection delay, CUV_DLY, which can be set from 10 ms to 6765 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:CUV:Delay configuration register.

When a CUV fault is triggered, the fault will recover if the voltage rises above the CUV threshold by a value of CUV_HYS, which is programmable from 100 mV to 1 V in steps of 50 mV, for Protections:Recovery:Time. This hysteresis level is set by the Protections:CUV:Recovery Hysteresis configuration register.

When CUV is triggered, the device turns off the DSG FET if configured for autonomous FET control, based on the setting in Settings:Protection:DSG FET Protections A[CUV] (the CHG FET remains enabled if already enabled). The device recovers (if configured for autonomous recovery), based on all cell voltages being above CUV threshold + CUV_HYS. Table 6-12 provides further details.

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

Table 5-12 Undervoltage Protection Operation

Status	Condition	Action
Normal	Min cell voltage > *Protections:CUV:Threshold*	Safety Alert A()[CUV] = 0
Alert	Min cell voltage ≤ *Protections:CUV:Threshold*	Safety Alert A()[CUV] = 1
Trip	Min cell voltage ≤ *Protections:CUV:Threshold* for *Protections:CUV:Delay* duration	Safety Alert A()[CUV] = 0 Safety Status A()[CUV] = 1 Alarm Raw Status()[XDSG] = 1 if configured for autonomous FET control
Recovery	Safety Status A()[CUV] = 1 and Min cell voltage > *Protections:CUV:Threshold* + *Protections:CUV:Recovery Hysteresis* for *Protections:Recovery:Time*	Safety Status A()[CUV] = 0 Alarm Raw Status()[XDSG] = 0 if configured for autonomous FET control

When a CUV fault is triggered, a snapshot of all cell voltages is captured and can be accessed through the 0x0080 CUV_SNAPSHOT() subcommand, which has the format shown below.

Table 5-13 0x0080 CUV_SNAPSHOT() Subcommand Format

Subcommand Address	Bytes Within Block	Name	Unit
0x0080	0–1	Cell 1 Voltage at CUV	mV
	2–3	Cell 2 Voltage at CUV	mV
	4–5	Cell 3 Voltage at CUV	mV
	6–7	Cell 4 Voltage at CUV	mV
	8–9	Cell 5 Voltage at CUV	mV
	10–11	Cell 6 Voltage at CUV	mV
	12–13	Cell 7 Voltage at CUV	mV
	14–15	Cell 8 Voltage at CUV	mV
	16–17	Cell 9 Voltage at CUV	mV
	18–19	Cell 10 Voltage at CUV	mV
	20–21	Cell 11 Voltage at CUV	mV
	22–23	Cell 12 Voltage at CUV	mV
	24–25	Reserved	‒
	26–27	Cell 13 Voltage at CUV	mV
	28–29	Reserved	‒
	30–31	Cell 14 Voltage at CUV	mV