7

LTC4050

4050f

at the CHRG pin and connect a weak current source to

ground, indicating that the battery is nearly fully charged

(C/10 occurs at approximately 94% charge).

An external capacitor on the TIMER pin sets the total

charge time. After a time-out occurs, the charge cycle is

terminated and the CHRG pin is forced high impedance. To

restart the charge cycle, remove the input voltage and

reapply it, or momentarily float the PROG pin.

Replacing the battery when charging will cause the timer

to be reset if the cell voltage of the new battery is below

3.88V (for 4.1V cells) or 3.98V (for 4.2V cells). If the

voltage is above 3.88V(for 4.1V cells) or 3.98V (for 4.2V

cells) the timer will continue for the remaining charge

time. In the case when a time out has occurred, a new

battery with a cell voltage of less than 3.88V or 3.98V can

be inserted and charged automatically with the full pro-

grammed charge time.

For batteries like lithium-ion that require accurate final

float voltage, the internal 2.47V reference, voltage ampli-

fier and the resistor divider provide regulation with

±1%

(max) accuracy.

The charger can be shut down by floating the PROG pin.

An internal current source will pull it high and clamp at

3.5V.

When the input voltage is not present, the charger goes

reduces the current drain on the battery and increases the

standby time.

OPERATIO

The LTC4050 is a linear battery charger controller. The

charge current is programmed by the combination of a

trimmed 800

to the input of the current amplifier (CA). The current

amplifier servos the gate of the external P-channel MOSFET

the charge current. When the voltage at the BAT pin

approaches the preset float voltage, the voltage amplifier

(VA) will start sinking current which reduces the voltage

above the UVLO level, a program resistor is connected

from the PROG pin to ground, and the NTC thermistor

temperature is between 0

°C and 50°C. At the beginning of

the charge cycle, if the battery voltage is below 2.49V, the

charger goes into trickle charge mode. The trickle charge

current is 10% of the full-scale current. If the cell voltage

stays low for one quarter of the total charge time, the

charge sequence will terminate.

The charger goes into the fast charge constant-current

mode after the voltage on the BAT pin rises above 2.49V.

In constant-current mode, the charge current is set by the

When the battery approaches the final float voltage, the

charge current will begin to decrease. When the current

drops to 10% of the full-scale charge current, an internal

comparator will turn off the pull-down N-channel MOSFET