LTC4054L-4.2 Datasheet, PDF (9/16 Pages) Linear Technology – 150mA Standalone Linear Li-Ion Battery Charger in ThinSOT

U
OPERATIO
LTC4054L-4.2
POWER ON
PROG
RECONNECTED
OR
UVLO CONDITION
STOPS
SHUTDOWN MODE
I_CC DROPS TO <25µA
CHRG: Hi-Z IN UVLO
WEAK PULL-DOWN
OTHERWISE
PROG FLOATED
OR
UVLO CONDITION
BAT < 2.9V
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
STANDBY MODE
NO CHARGE CURRENT
CHRG: WEAK
PULL-DOWN
2.9V < BAT < 4.05V
4054L42 F01
Figure 1. State Diagram of a Typical Charge Cycle
Charge Status Indicator (CHRG)
The charge status output has three different states: strong
pull-down (~10mA), weak pull-down (~20uA), and high
impedance. The strong pull-down state indicates that the
LTC4054L is in a charge cycle. Once the charge cycle has
terminated, the pin state is determined by undervoltage
lockout conditions. A weak pull-down indicates that V_CC
meets the UVLO conditions and the LTC4054L is ready to
charge. High impedance indicates that LTC4054L is in
undervoltage lock-out mode: either V_CC is within 100mV
of the BAT pin voltage or insufficient voltage is applied to
the V_CC pin. A microprocessor can be used to distinguish
between these three states—this method is discussed 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 LTC4054L 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 LTC4054L. 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.
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