BQ76PL536PAP datasheet(20/58 Pages) TI

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VC6

VC5

VC4

VC3

VC2

VC1

COV_FAULT

FAULT

FORCE

POR

CRC

CUV

COV

FAULT

ALERT

ECC_

COR

UVLO

CBT

DRDY

STATUS

COVT Filter

FAULT _S

FAULT _H

FAULT _N

Latch

–

COVCOMPARATOR

(onepercell)

–

PROTECTOR

REFERENCE

CONFIG_COV[]

VC6

LEVEL

SHIFTER

TRIP

SETPOINT

VSS

bq76PL536

SLUSA08A – DECEMBER 2009 – REVISED JULY 2010

www.ti.com

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 CUVT, and CUVT, this can

cause an error greater than the 10% maximum specified for delays <500 µs.

Figure 6. COV FAULT Simplified Logic Tree

Cell Undervoltage Fault Detection (CUV)

Cell undervoltage detection operates in a similar manner to the COV protection. When the voltage across a cell

falls below the programmed CUV threshold (CONFIG_CUV[]) for a period of time greater than CUVT

(CONFIG_CUVT[]), the CUV_FAULT[] flag for that cell is set. The bits in CUV_FAULT[] are then ORed into the

FAULT[CUV] flag, which is then ORed into the DEVICE_STATUS[FAULT] flag, which causes the FAULT_S (_H)

pin also to be asserted. The CUV flag is latched unless CUVT 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[CUV], followed by a 0 to FAULT[CUV].

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