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LTC4061

4061fd

operaTion

The LTC4061 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

LTC4061includesaninternalP-channelpowerMOSFETand

thermal regulation circuitry. No blocking diode or external

sense resistor is required; thus, the basic charger circuit

requires only two external components.

NormalOperation

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 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 LTC4061

enters constant voltage mode and the charge current

decreases as the battery becomes fully charged.

The LTC4061 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 VCC disables internal termination, allowing

externalchargeuserterminationthroughthe ENinput.See

Applications Information for more information on charge

termination methods.

ProgrammingChargeCurrent

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:

PROG

CHG

PROG

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:

BAT

PROG

• 1000

SmartStart

When the LTC4061 is initially powered on or brought out

of shutdown mode, the charger checks the battery volt-

age. If the BAT pin is below the recharge threshold of 4.1V

(which corresponds to approximately 80-90% battery

capacity), the LTC4061 enters charge mode and begins a

full charge cycle. If the BAT pin is above 4.1V, the LTC4061

enters standby mode and does not begin charging. This

featurereducesthenumberofunnecessarychargecycles,

prolonging battery life.

AutomaticRecharge

When the charger is in standby mode, the LTC4061

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

is being used). This feature eliminates the need for peri-

odic charge cycle initiations and ensures that the battery

is always fully charged. Automatic recharge is disabled

in user termination mode.

ThermalRegulation

Aninternalthermalfeedbackloopreducestheprogrammed

charge current if the die temperature attempts to rise

above a preset value of approximately 105°C. This feature

protects the LTC4061 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. 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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