Datasheet

LTC4063
9
4063fc
operaTion
The LTC4063 is designed to charge a single cell lithium-
ion battery and supply a regulated output voltage for
battery-powered applications. Using the constant current/
constant voltage algorithm, the charger can deliver up to
1A of charge current with a final float voltage accuracy of
±0.35%. The LTC4063 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.
The LDO regulator is powered from the battery terminal
and can be programmed for output voltages between 1.2V
and 4.2V using external resistors. An output capacitor is
required on the OUT pin for stability and improved transient
response. A low ESR capacitor of ≥2µF should be used.
Normal
Operation
The charge cycle begins when the voltage at the V
CC
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 LTC4063 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 (4.2V), the LTC4063
enters constant-voltage mode and the charge current
decreases as the battery becomes fully charged.
The LTC4063 offers several methods with which to ter-
minate a charge cycle. Connecting an external capacitor
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 V
CC
disables internal termination, allowing
external charge termination to be used by the CHGEN
input. See Applications Information for more on charge
termination methods.
Programming
the Charge Current
The charge current is programmed using a single resistor
from the PROG pin to ground. The battery charge cur-
rent is 1000 times the current out of the PROG pin. The
program resistor and the charge current are calculated by
the following equations:
R
V
I
I
V
R
PROG
CHG
CHG
PROG
= =
1000 1000
,
The charge current out of the BAT pin can be determined
at any time by monitoring the PROG pin voltage and ap-
plying the following equation:
I
V
R
BAT
PROG
PROG
= 1000
SmartStart
When the LTC4063 is initially powered on or brought out
of shutdown mode, the charger checks the voltage on
BAT. If the BAT pin is below the recharge threshold of 4.1V
(which corresponds to approximately 80% to 90% battery
capacity), the LTC4063 enters charge mode and begins a
full charge cycle. If the BAT pin is above 4.1V, the LTC4063
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 LTC4063
continuously monitors the voltage on the BAT pin. When
the BAT pin voltage drops below 4.1V, the charge cycle is
automatically restarted and the internal timer is reset to
50% the programmed charge time (if time termination 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