Datasheet

- - VC6 VC5 VC4 VC3 VC2 VC1
COV_FAULT
- -
I_
FAULT
FORCE
POR CRC CUV COV
FAULT
AR FAULT ALERT -
ECC_
COR
UVLO CBT DRDY
STATUS
COVT Filter
ANALOG TRANSLATION
FAULT _S
FAULT _H
FAULT _N
Latch
+
–
COVCOMPARATOR
(onepercell)
+–
PROTECTOR
REFERENCE
CONFIG_COV[]
VC6
LEVEL
SHIFTER
TRIP
SETPOINT
VSS
bq76PL536-Q1
www.ti.com SLUSAB1 –MAY 2011
A separate timer is provided for each fault source (cell overvoltage, cell undervoltage, overtemperature) to
prevent false alarms. Each timer is programmable from 100 µs to more than 3 s. The timers may also be
disabled, which causes fault conditions to be sensed immediately and not latched.
The clearing of the FAULT or ALERT flag (and pin) occurs when the respective flag is written to a 1, which also
restarts the respective fault timer. This also clears the FAULT_S (_H) or ALERT_S (_H) pin. If the actual fault
remains present, the FAULT (ALERT) pin is again asserted at the expiration of the timer. This cycle repeats until
the cause of the fault is removed.
On exit from the SLEEP state, the COV, CUV, and OT fault comparators are disabled for approximately 200 µs
to allow internal circuitry to stabilize and prevent false error condition detection.
Using the Protector Functions With 3-5 Cells
The OV/UV condition can be ignored for unused channels by setting the FUNCTION_CONFIG[CNx] bits to the
maximum number of cells connected to the device. If fewer than 6 cells are configured, the corresponding OV/UV
faults are ignored. For example, if the FUNCTION_CONFIG[] bits are set to xxxx 1000, then the OV/UV
comparators are disabled for cells 5 and 6. Correct setting of this register prevents spurious false alarms.
Cell Overvoltage Fault Detection (COV)
When the voltage across a cell exceeds the programmed COV threshold for a period of time greater than set in
the COV timer (COVT), the COV_FAULT[] flag for that cell is set. The bits in COV_FAULT[] are then ORed into
the FAULT[COV] flag, which is then ORed into the DEVICE_STATUS[FAULT] flag, which causes the FAULT_S
(_H) pin also to be asserted. The COV flag is latched unless COVT is programmed to 0, in which case the flag
follows the fault condition. Care should be taken when using this setting to avoid chatter of the fault status. To
reset the FAULT flag, first remove the source of the fault (i.e., the overvoltage condition) and then write a 1 to
FAULT[COV], followed by a 0 to FAULT[COV].
The voltage trip point is set in the CONFIG_COV register. Set points are spaced every 50 mV. Hysteresis is
provided to avoid chatter of the fault sensing. The filter delay time is set in the CONFIG_COVT[] register to
prevent false alarms. A start-up deglitch circuit is applied to the timers to prevent false triggering. The deglitch
time is 0–50 µs, and introduces a small error in the timing for short times. For both COVT and CUVT, this can
cause an error greater than the 10% maximum specified for delays <500 µs.
Figure 6. COV FAULT Simplified Logic Tree
Copyright © 2011, Texas Instruments Incorporated 21