Datasheet

LTC4054L-4.2
9
4054l42fa
operaTion
Charge Status Indicator (CHRG)
The charge status output has three different states: strong
pull-down (~10mA), weak pull-down (~20µA), 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
considerations are discussed further in the Applications
Information 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.
TRICKLE CHARGE
MODE
1/10TH FULL CURRENT
BAT > 2.9V
BAT < 2.9V
BAT > 2.9V
CHRG: STRONG
PULL-DOWN
CHARGE MODE
FULL CURRENT
CHRG: STRONG
PULL-DOWN
SHUTDOWN MODE
CHRG: Hi-Z IN UVLO
WEAK PULL-DOWN
OTHERWISE
PROG
RECONNECTED
OR
UVLO CONDITION
STOPS
PROG FLOATED
OR
UVLO CONDITION
I
CC
DROPS TO <25A
POWER ON
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