bq20z80-V101
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SLUS625D–SEPTEMBER 2004–REVISED OCTOBER 2005
Charge and Zero-Volt Charge FET Fault Protection
If the bq20z80 has at any time attempted to turn off the CHG or ZVCHG FETs, or AFE.OUTPUT [CHG] is set,
and a level of charge SBS.Current( ) continues to flow that is ≥ DF:FET Fail Limit for a period of DF:FET Fail
Time, then a CHG FET fault is reported.
When the first occurrence of excessive level of charge SBS.Current( ) is detected, SBS.PFAlert( ) [CFETF] is set,
and the bq20z80 attempts to turn off the CHG and ZVCHG FET again. SBS.PFAlert( ) [CFETF] is cleared if at
any time before the expiration of DF:FET Fail Time, the current is measured below the DF:FET Fail Limit
threshold.
If DF:Permanent Fail Cfg [XCFETF] is set, the SAFE pin is driven low and the SAFE pin is driven high. If DF:FET
Fail Time is set to 0, this feature is disabled.
NAME
CLASS / SUBCLASS
FORMAT
VALID RANGE
0 to 500
SIZE (BYTES)
UNITS
mA
DEFAULT VALUE
20
FET Fail Limit
FET Fail Time
2
1
2nd Level Safety /
FET Verification (18)
Integer
0 to 30
s
0 (2 typical)
Discharge FET Fault Protection
If the bq20z80 has at any time attempted to turn off the DSG FET, or AFE.OUTPUT [DSG] is set, and a level of
discharge SBS.Current( ) continues to flow ≥ (-) DF:FET Fail Limit for a period of DF:FET Fail Time, then a
DSG FET fault is reported. If DF:FET Fail Time is set to 0, the feature is completely disabled.
When the first occurrence of excessive level of discharge SBS.Current( ) is detected, SBS.PFAlert( ) [DFETF] is
set, and the bq20z80 attempts to turn off the DSG FET again. SBS.PFAlert( ) [DFETF] is cleared if at any time
before the DF:FET Fail Time times out, the current is measured below the (-) DF:FET Fail Limit threshold.
If DF:Permanent Fail Cfg [XDFETF] is set, the SAFE pin is driven low and the SAFE pin is driven high. If DF:FET
Fail Time is set to 0, this feature is disabled.
AFE Communication Fault Protection (AFE_C)
The bq20z80 continuously validates its read and write communications with the bq29312A. If either a read or
write verify fails, an internal AFE_Fail_Counter is incremented. If the AFE_Fail_Counter > DF:AFE Fail Limit, the
bq20z80 reports a permanent failure. If the DF:AFE Fail Limit is set to 0, this feature is not disabled, but reports a
permanent failure after only one AFE communication fault. An AFE_C fault could also be declared if after a full
reset the initial offset values read from the AFE cannot be verified. These values are A-to-D readings of the
bq29312A VCELL output. The bq29312A offset values are verified by reading the values twice and confirming
that the readings are within acceptable limits. If the offset value verification fails an AFE_C fault is declared.
The internal AFE_Fail_Counter is decremented by one count each DF:AFE Fail Recovery Time.
If DF:Permanent Fail Cfg [XAFE_C] is set, the SAFE pin is driven low and the SAFE pin is driven high.
SIZE
(BYTES)
NAME
CLASS / SUBCLASS FORMAT
VALID RANGE
UNITS
DEFAULT VALUE
AFE Fail Limit
2nd Level Safety /
AFE Verification (20)
0 to 255
0 to 255
1
1
counts
s
10
20
Integer
AFE Fail Recovery Time
23
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