LTC4054-4.2/LTC4054X-4.2
U
OPERATIO
lockout conditions. A weak pull-down indicates that VCC
meets the UVLO conditions and the LTC4054 is ready to
charge. High impedance indicates that the LTC4054 is in
undervoltagelockoutmode:eitherVCC is less than 100mV
above theBATpinvoltageorinsufficientvoltageisapplied
to the VCC pin. A microprocessor can be used to distin-
guish between these three states—this method is dis-
cussed in the Applications Information section.
than 2µA and the supply current to less than 50µA. A new
charge cycle can be initiated by reconnecting the program
resistor.
In manual shutdown, the CHRG pin is in a weak pull-down
state as long as VCC is high enough to exceed the UVLO
conditions. The CHRG pin is in a high impedance state if
the LTC4054 is in undervoltage lockout mode: either VCC
iswithin100mVoftheBATpinvoltageorinsufficientvoltage
is applied to the VCC pin.
Thermal Limiting
Aninternalthermalfeedbackloopreducestheprogrammed
charge current if the die temperature attempts to rise
above a preset value of approximately 120°C. This feature
protects the LTC4054 from excessive temperature and
allows the user to push the limits of the power handling
capabilityofagivencircuitboardwithoutriskofdamaging
the LTC4054. The charge current can be set according to
typical (not worst-case) ambient temperature with the
assurance that the charger will automatically reduce the
current in worst-case conditions. ThinSOT power consid-
erationsarediscussedfurtherintheApplicationsInforma-
tion section.
Automatic Recharge
Oncethechargecycleisterminated,theLTC4054continu-
ously monitors the voltage on the BAT pin using a com-
parator with a 2ms filter time (tRECHARGE). A charge cycle
restarts when the battery voltage falls below 4.05V (which
corresponds to approximately 80% to 90% battery capac-
ity). This ensures that the battery is kept at or near a fully
charged condition and eliminates the need for periodic
charge cycle initiations. CHRG output enters astrong pull-
down state during recharge cycles.
POWER ON
BAT < 2.9V
Undervoltage Lockout (UVLO)
TRICKLE CHARGE
MODE
PROG
RECONNECTED
OR
UVLO CONDITION
STOPS
Aninternalundervoltagelockoutcircuitmonitorstheinput
voltageandkeepsthechargerinshutdownmodeuntilVCC
risesabovetheundervoltagelockoutthreshold. TheUVLO
circuit has a built-in hysteresis of 200mV. Furthermore, to
protect against reverse current in the power MOSFET, the
UVLO circuit keeps the charger in shutdown mode if VCC
falls to within 30mV of the battery voltage. If the UVLO
comparator is tripped, the charger will not come out of
shutdown mode until VCC rises 100mV above the battery
voltage.
1/10TH FULL CURRENT
CHRG: STRONG
PULL-DOWN
BAT > 2.9V
BAT > 2.9V
SHUTDOWN MODE
DROPS TO <25µA
CHARGE MODE
I
CC
FULL CURRENT
CHRG: Hi-Z IN UVLO
WEAK PULL-DOWN
OTHERWISE
CHRG: STRONG
PULL-DOWN
PROG < 100mV
STANDBY MODE
NO CHARGE CURRENT
PROG FLOATED
OR
UVLO CONDITION
CHRG: WEAK
PULL-DOWN
Manual Shutdown
2.9V < BAT < 4.05V
At any point in the charge cycle, the LTC4054 can be put
into shutdown mode by removing RPROG thus floating the
PROG pin. This reduces the battery drain current to less
405442 F01
Figure 1. State Diagram of a Typical Charge Cycle
405442xf
9
Linear [ Linear ]
