bq20z80-V101
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SLUS625D–SEPTEMBER 2004–REVISED OCTOBER 2005
Short-Circuit Protection
The bq20z80 short-circuit protection is controlled by the bq29312A, but is recovered by the bq20z80. This allows
different recovery methods to accommodate various applications.
The bq29312A charge short-circuit and discharge short-circuit protection are configured by the bq20z80 in
DF:AFE SC Chg Cfg (see bq29312A SCC register) and DF:AFE SC Dsg Cfg (see bq29312A SCD register),
respectively. See the 'Short-circuit Detection' section of the bq29312A data sheet for more details and the
appropriate values to use.
SBS.SAFETYSTATUS( )
AND DF:Nonremovable Cfg
Short Circuit
DF NAME
FET
DF CLEAR THRESHOLD
Charge
AFE SC Chg Cfg
AFE SC Dsg Cfg
CHG
DSG
ASCC
ASCD
AFE SC Recovery
Discharge
When the bq29312A detects a short circuit in charge or short circuit in discharge fault, the charge and discharge
FETs are turned off, the XALERT pin of the bq20z80 is driven low by the XALERT pin of the bq29312A and the
bq29312A is interrogated. When the bq20z80 identifies the short-circuit condition (charge or discharge current
direction), the internalAFE_Current_Fault timer is started from 0, either of SBS.BatteryStatus( ) [TCA, TDA] are
set, SBS.ChargingCurrent( ) and SBS.ChargingVoltage( ) is set to 0, and SBS.SafetyStatus( ) [ASCC, ASCD] is
set. If the short-circuit condition is in discharge, then SBS.OperationStatus( ) [XDSG] is also set.
However, when the bq20z80 has SBS.SafetyStatus( ) [ASCC[ set, the CHG FET is turned on again, as long as
SBS.Current( ) is reported to ≤ DF:Dsg Current Threshold. Also, when the bq20z80 has SBS.SafetyStatus( )
[SCD[ 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 of charge- or
discharge-FET body diode during operation. This action is not affected by the state of DF:Operation Cfg B [NR].
Each bq20z80 short-circuit protection feature can be individually configured to recover via two different methods,
based on DF:Operation Cfg B [NR].
Standard Recovery is where DF:Operation Cfg B [NR] = 0 and the overcurrent tier is not selected in
DF:Non-Removable Cfg. When the pack is removed and re-inserted, the condition is cleared. Pack removal and
re-insertion is detected by transition on the PRES input from low to high to low. When the tier is not selected in
DF:Non-Removable Cfg, that particular feature uses the Nonremovable Battery Mode recovery.
Nonremovable Battery Mode Recovery is where DF:Operation Cfg
B [NR] = 1. The state of
DF:Non-Removable Cfg has no consequence when DF:Operation Cfg B [NR] = 1. This recovery requires
SBS.AverageCurrent( ) to be ≤ DF:AFE SC Recovery threshold and for the internal AFE_Current_Fault timer to
be ≥ DF:Current Recovery Time.
When the recovery condition for a charging fault is detected, the charge FET is allowed to be turned on if other
safety and configuration states permit. The ZVCHG FET is turned off if DF:Operation Cfg A [ZVCHG1, ZVCHG0]
are set appropriately. When this occurs, SBS.BatteryStatus( ) [TCA] is reset, SBS.ChargingCurrent( ) and
SBS.ChargingVoltage( ) are set to the appropriate values per the charging algorithm, and the appropriate
SBS.SafetyStatus( ) flag is reset.
When the recovery condition for a discharging fault is detected, the discharge FET is allowed to be turned on if
other safety and configuration states permit. The ZVCHG FET is turned off if DF:Operation Cfg A [ZVCHG1,
ZVCGH0] are set appropriately. When this occurs SBS.BatteryStatus( ) [TDA] is reset, SBS.ChargingCurrent( )
and SBS.ChargingVoltage(
)
are set to the appropriate value per the charging algorithm, and
SBS.OperationStatus( ) [XDSG] and the appropriate SBS.SafetyStatus( ) flags are reset.
VALID
RANGE
SIZE
(BYTES)
DEFAULT
VALUE
NAME
CLASS / SUBCLASS
FORMAT
UNITS
Low Nibble = AFE SC Chg
High Nibble = AFE SC Chg Time
Low Nibble = AFE SC Dsg
High Nibble = AFE SC Dsg Time
Integer
AFE SC Chg Cfg
0x77
0x00 to
0xff
Hex
1
2
N/A
mA
1st Level Safety /
Current (1)
AFE SC Dsg Cfg
AFE SC Recovery
0x77
1
0 to 200
16
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