LTC4062_15 Datasheet, PDF (9/20 Pages) Linear Technology – Standalone Linear Li-Ion Battery Charger with Micropower Comparator

LTC4062
OPERATIO
The LTC4062 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 ±0.35%. The
LTC4062 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 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
LTC4062 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 LTC4062
enters constant voltage mode and the charge current
decreases as the battery becomes fully charged.
The LTC4062 offers several methods with which to termi-
nate 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 resistor to the
I_DET 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
user 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:
R_PROG
=
1000V
I_CHG
,
I_CHG
=
1000V
R_PROG
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:
I_BAT
=
V_PROG
R_PROG
• 1000
SmartStart
When the LTC4062 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 4.1V
(which corresponds to approximately 80-90% battery
capacity), the LTC4062 enters charge mode and begins a
full charge cycle. If the BAT pin is above 4.1V, the LTC4062
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 LTC4062
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% of the programmed charge time (if time termination
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