LTC4061-4.4 데이터 시트보기 (PDF) - Linear Technology
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LTC4061-4.4 Datasheet PDF : 20 Pages
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OPERATIO
The LTC4061-4.4 is designed to charge single-cell
lithium-ion batteries. Using the constant current/constant
voltage algorithm, the charger can deliver up to 1A of
charge current with a final float voltage accuracy of ±0.4%.
The LTC4061-4.4 includes an internal P-channel power
MOSFET and thermal regulation circuitry. No blocking
diode or external sense resistor is required; thus, the basic
charger circuit requires only two external components.
Normal Operation
The charge cycle begins when the voltage at the VCC pin
rises above the UVLO level and a discharged battery is
connected to BAT. If the BAT pin voltage is below 2.9V,
the charger enters trickle charge mode. In this mode, the
LTC4061-4.4 supplies 1/10th of the programmed charge
current in order to bring the battery voltage up to a safe
level for full current charging.
Once the BAT pin voltage rises above 2.9V, the charger
enters constant current mode, where the programmed
charge current is supplied to the battery. When the BAT
pin approaches the final float voltage (4.375V), the
LTC4061-4.4 enters constant voltage mode and the charge
current decreases as the battery becomes fully charged.
The LTC4061-4.4 offers several methods with which to
terminate a charge cycle. Connecting an external capaci-
tor to the TIMER pin activates an internal timer that stops
the charge cycle after the programmed time period has
elapsed. Grounding the TIMER pin and connecting a resis-
tor to the IDET pin causes the charge cycle to terminate
once the charge current falls below a set threshold when
the charger is in constant voltage mode. Connecting the
TIMER pin to VCC disables internal termination, allowing
external user charge termination through the EN input.
See Applications Information for more information on
charge termination methods.
Programming Charge Current
The charge current is programmed using a single resistor
from the PROG pin to ground. When the charger is in the
constant current mode, the voltage on the PROG pin is
1V. The battery charge current is 1000 times the current
out of the PROG pin. The program resistor and the charge
current are calculated by the following equations:
LTC4061-4.4
RPROG
=
1000V
ICHG
,
ICHG
=
1000V
RPROG
The charge current out of the BAT pin can be determined
at any time by monitoring the PROG pin voltage and
applying the following equation:
IBAT
=
VPROG
RPROG
• 1000
SmartStart
When the LTC4061-4.4 is initially powered on or brought
out of shutdown mode, the charger checks the battery
voltage. If the BAT pin is below the recharge threshold
of 4.275V (which corresponds to approximately 80-90%
battery capacity), the LTC4061-4.4 enters charge mode
and begins a full charge cycle. If the BAT pin is above
4.275V, the LTC4061-4.4 enters standby mode and does
not begin charging. This feature reduces the number of
unnecessary charge cycles, prolonging battery life.
Automatic Recharge
When the charger is in standby mode, the LTC4061-4.4
continuously monitors the voltage on the BAT pin. When
the BAT pin voltage drops below 4.275V, the charge cycle
is automatically restarted and the internal timer is reset
to 50% of the programmed charge time (if time termina-
tion is being used). This feature eliminates the need for
periodic charge cycle initiations and ensures that the battery
is always fully charged. Automatic recharge is disabled in
user termination mode.
Thermal Regulation
An internal thermal feedback loop reduces the programmed
charge current if the die temperature attempts to rise
above a preset value of approximately 105°C. This feature
protects the LTC4061-4.4 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 LTC4061-4.4. The charge current can be set according
to typical (not worst-case) ambient temperatures with the
assurance that the charger will automatically reduce the
current in worst-case conditions.
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