LTC4054X-4.2_15 Datasheet, PDF (9/16 Pages) Linear Technology – Standalone Linear Li-Ion Battery Charger with Thermal Regulation in ThinSOT

U
OPERATIO
lockout conditions. A weak pull-down indicates that V_CC
meets the UVLO conditions and the LTC4054 is ready to
charge. High impedance indicates that the LTC4054 is in
undervoltage lockout mode: either V_CC is less than 100mV
above the BAT pin voltage or insufficient voltage is applied
to the V_CC pin. A microprocessor can be used to distin-
guish between these three states—this method is dis-
cussed in the Applications Information section.
Thermal Limiting
An internal thermal feedback loop reduces the programmed
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
capability of a given circuit board without risk of damaging
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-
erations are discussed further in the Applications Informa-
tion section.
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in shutdown mode until V_CC
rises above the undervoltage lockout threshold. The UVLO
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 V_CC
falls to within 30mV of the battery voltage. If the UVLO
comparator is tripped, the charger will not come out of
shutdown mode until V_CC rises 100mV above the battery
voltage.
Manual Shutdown
At any point in the charge cycle, the LTC4054 can be put
into shutdown mode by removing R_PROG thus floating the
PROG pin. This reduces the battery drain current to less
LTC4054-4.2/LTC4054X-4.2
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 V_CC 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 V_CC
is within 100mV of the BAT pin voltage or insufficient voltage
is applied to the V_CC pin.
Automatic Recharge
Once the charge cycle is terminated, the LTC4054 continu-
ously monitors the voltage on the BAT pin using a com-
parator with a 2ms filter time (t_RECHARGE). 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 a strong pull-
down state during recharge cycles.
POWER ON
BAT < 2.9V
PROG
RECONNECTED
OR
UVLO CONDITION
STOPS
SHUTDOWN MODE
I_CC DROPS TO <25µA
CHRG: Hi-Z IN UVLO
WEAK PULL-DOWN
OTHERWISE
TRICKLE CHARGE
MODE
1/10TH FULL CURRENT
CHRG: STRONG
PULL-DOWN
BAT > 2.9V
CHARGE MODE
BAT > 2.9V
FULL CURRENT
CHRG: STRONG
PULL-DOWN
PROG < 100mV
PROG FLOATED
OR
UVLO CONDITION
STANDBY MODE
NO CHARGE CURRENT
CHRG: WEAK
PULL-DOWN
2.9V < BAT < 4.05V
405442 F01
Figure 1. State Diagram of a Typical Charge Cycle
405442xf
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