bq20z80-V101
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SLUS625D–SEPTEMBER 2004–REVISED OCTOBER 2005
Overtemperature Protection
The bq20z80 has overtemperature protection for both charge and discharge conditions. In either case, if
SBS.Temperature( ) is ≥ the protection threshold for a period ≥ the protection delay time, then action is taken.
However, if the delay time is set to 0, then the feature is disabled.
SBS.SAFETYALERT( )
SBS.SAFETYSTATUS( )
DF CLEAR
THRESHOLD
DF THRESHOLD
DF TIME
FET
Charge
Over Temp Chg
Over Temp Chg
OT Chg Time
OT Dsg Time
CHG
DSG
OTC
OTD
OT Chg Recovery
OT Dsg Recovery
Discharge
During the period between detection of excessive temperature and the expiration of the timer, the respective
SBS.SafetyAlert( ) bit is set. If the timer expires or SBS.Temperature( ) returns within the normal operation range,
the SBS.SafetyAlert( ) bit is cleared.
If SBS.SafetyStatus( ) [OTC] becomes set and if DF:Operation Cfg B [OTFET] is set, the CHG FET is turned off
and the ZVCHG FET turned off, if DF:Operation Cfg A [ZVCHG1, ZVCHG0] are set appropriately. If
SBS.SafetyStatus( ) [OTD] becomes set and if DF:Operation Cfg B [OTFET] is set, the DSG FET turns off. If the
DF:Operation Cfg B [OTFET] bit is cleared, no FET action is taken. Also, SBS.BatteryStatus( ) [OTA] is set,
SBS.ChargingCurrent( ) and SBS.ChargingVoltage( ) are set to 0, either of SBS.BatteryStatus( ) [TCA, TDA] is
set, and the corresponding flag in SBS.SafetyStatus( ) is set. If SBS.SafetyStatus( ) [OTD] is set AND
DF:Operation Cfg B [OTFET] is set then SBS.OperationStatus( ) [XDSG] is set.
However, when SBS.SafetyStatus( ) [OTC] is set, the CHG FET is turned on again, as long as SBS.Current( ) is
reported to be ≤ (-) DF:Dsg Current Threshold. Also, when the bq20z80 has SBS.SafetyStatus( ) [OTD] set, the
DSG FET is turned on again, as long as SBS.Current( ) is reported to be ≤ DF:Chg Current Threshold. No other
flags change state until full recovery is reached. This prevents overheating the respective FET's body diode
during operation. This action is not affected by the state of DF:Operation Cfg B [NR].
For normal recovery to be achieved, SBS.Temperature( ) must be ≤ the respective DF:OT Chg Recovery or
DF:OT Dsg Recovery. When this occurs, the FETs are returned to the normal operating state if applicable,
SBS.BatteryStatus(
)
[OTA] is cleared, either of SBS.BatteryStatus(
)
[TCA, TDA] is cleared,
SBS.ChargingCurrent( ) and SBS.ChargingVoltage( ) are set to the appropriate values per the charging
algorithm, and the appropriate SBS.SafetyStatus( ) flag is reset. If SBS.SafetyStatus( ) [OTD] is cleared, then
SBS.OperationStatus( ) [XDSG] is cleared.
VALID
RANGE
SIZE
(BYTES)
DEFAULT
VALUE
NAME
CLASS / SUBCLASS
FORMAT
UNITS
Over Temp Chg
OT Chg Recovery
OT Chg Time
0 to 1200
0 to 1200
0 to 60
2
2
1
2
1
2
0.1°C
0.1°C
s
550
500
2
1st Level Safety / Temperature (2)
Integer
Over Temp Dsg
OT Dsg Time
0 to 1200
0 to 30
0.1°C
s
600
2
OT Dsg Recovery
0 to 1200
0.1°C
550
AFE Watchdog
The bq29312A incorporates a watchdog feature that automatically turns off the CHG, DSG, and ZVCHG FETs if
the bq29312A does not receive the appropriate frequency input on the WDI pin. The bq20z80 has no warning
that this is about to happen, but it can report the occurrence, once the bq20z80 is able to interrogate the
bq29312A.
When the XALERT input of the bq20z80 is triggered by the XALERT pin of the bq29312A, the bq20z80 reads
AFE.STATUS. If AFE.STATUS [WDF] is set, then SBS.Safety Status( ) [WDF] is set, and periodic verification of
the bq29312A RAM is undertaken. If verification of the bq29312A RAM fails then SBS.SafetyStatus( ) [WDF] is
set and the FET?s will turn off. Verification of the bq29312A RAM will continue every second. If the periodic
verification passes, then SBS.SafetyStatus( ) [WDF] is cleared and the FETs returned to normal operation. If
DF:AFE Check Time = 0 then on detection of a verification fault the DF:PF Flags 1 [AFE_C] will NOT be set and
PF mode will NOT be entered. If DF:AFE Check Time is not 0 then if DF:AFE Check Time attempts of the
verification fail, the bq20z80 sets DF:PF Flags 1 [AFE_P] and enters permanent failure. See Periodic AFE
Verification for further details.
17
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