
LTC4099
4099fd
viaI2C(adisablefollowedbyanenable).Ifthebadcell
indicationreturns,thenthecellisdefinitivelybad.
Bit4indicatesthatthebatterychargerisinthermalregula-
tionduetoexcessiveLTC4099junctiontemperature.Recall
thattherearetwoI2Cprogrammablejunctiontemperature
settingsavailableatwhichtoregulate,85°Cand105°C.
Bit4indicatesthermalregulationatwhicheversettingis
chosen.
Bits3and2indicatethestatusofthethermistormeasure-
mentcircuitandaredecodedinTable7.TheBATTERY
TOOCOLDandBATTERYTOOHOTstatesindicatethat
thethermistortemperatureisoutofrange(eitherbelow
0°C or above 45°C for a curve 2 thermistor) and that
charginghaspauseduntilareturntovalidtemperature.
TheBATTERYOVERTEMPERATUREstateindicatesthat
thebattery’sthermistorhasreachedacriticaltemperature
(above60°Cforacurve2thermistor)andthatlongterm
battery capacity may be seriously compromised if the
conditionpersists.
Table 7. NTC1, NTC0 Decode
THERMISTOR STATUS BIT DECODE
NTC1
NTC0
THERMISTOR STATUS
0
NONTCFAULT
0
1
BATTERYTOOCOLD
1
0
BATTERYTOOHOT
1
BATTERYOVERTEMPERATURE
Table 8. CHRGR1, CHRGR0 Decode
BATTERY CHARGER STATUS BIT DECODE
CHRGR1
CHRGR0
CHARGER STATUS
0
CHARGEROFF
0
1
CONSTANT-CURRENT
1
0
CONSTANTV,IBAT>C/x
1
CONSTANTV,IBAT<C/x
Bits1and0indicatethestatusofthebatterycharger,and
aredecodedintooneoffourpossiblebatterychargerstates
inTable8.Theconstant-currentstateindicatesthatthe
batterychargerisattemptingtochargewithallavailable
current up to the constant-current level programmed,
andthatthebatteryhasnotyetreachedthefloatvoltage.
TheCONSTANTV,IBAT>C/xbitindicatesthatthebattery
chargerhasenteredthefloatvoltagephaseofcharging
(BATat4.1Vor4.2V),butthatthechargecurrentisstill
abovetheC/xdetectionlevelprogrammed.TheCONSTANT
V,IBAT<C/xbitindicatesthatthebatterychargecurrent
hasdroppedbelowtheC/xdetectionlevelprogrammed,
andthatchargingisvirtuallycomplete.Notethatifthe
currentlimitedUSBcompliantswitchingregulatorisin
inputcurrentregulation,thentheactualbatterycharge
currentmaybelessthanC/xduetoinsufficientavailable
power.IftheLTC4099isininputcurrentlimit,thecharge
statusbitswilllockout(disallow)thestate1-1,indicating
thatchargingiscomplete.Thisfeaturepreventsfalsefull
capacitychargeindicationsduetoinsufficientpowerto
thebatterycharger.
ThestatusreadfromtheLTC4099iscapturedinoneof
twoways.Ifaninterruptiscurrentlypending,thenthe
availabledatarepresentsthestateoftheLTC4099atthe
timetheinterruptwasgenerated.Ifnointerruptispending,
thenthedataiscapturedwhentheLTC4099acknowledges
itsreadaddress.Inthecaseofapendinginterrupt,fresh
datacanbeassuredbytakingtwoconsecutivereadings
ofthestatusinformationanddiscardingthefirstset.
Shutdown Mode
TheUSBswitchingregulatorisenabledwheneverVBUS
isaboveVUVLO,greaterthanVDUVLOaboveBATandthe
LTC4099isnotinoneofthetwoUSBsuspendmodes
(500Aor2.5mA).Whenpowerisavailablefromboth
theUSB(VBUS)andWALLinputs,theauxiliary(WALL)
input is prioritized and the USB switching regulator is
disabled.
Thebatterychargerwillalwaysstartachargecyclewhen
powerisdetectedatVBUSorWALL.Itcanonlybeshut
down via a command from the I2C port or by normal
terminationafterachargecycle.
The ideal diode is enabled at all times and cannot be
disabled.
operaTion