LTC4098-1 datasheet(18/32 Pages) LINER

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LTC4098/LTC4098-1

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Charge Termination

The battery charger has a built-in safety timer. Once the

voltage on the battery reaches the preprogrammed ﬂoat

voltage of 4.200V for the LTC4098 or 4.100V for the

LTC4098-1, the charger will regulate the battery voltage

there and the charge current will decrease naturally. Once

the charger detects that the battery has reached 4.200V

or 4.100V respectively, the 4-hour safety timer is started.

After the safety timer expires, charging of the battery will

discontinue and no more current will be delivered.

Automatic Recharge

Once the battery charger terminates, it will remain off

drawing only microamperes of current from the battery.

If the portable product remains in this state long enough,

the battery will eventually self discharge. To ensure that

the battery is always topped off, a charge cycle will au-

tomatically begin when the battery voltage falls below

VRECHRG (typically 4.1V for the LTC4098 and 4.0V for the

LTC4098-1). In the event that the safety timer is running

when the battery voltage falls below VRECHRG, it will reset

back to zero. To prevent brief excursions below VRECHRG

from resetting the safety timer, the battery voltage must

be below VRECHRG for more than 1.5ms. The charge

cycle and safety timer will also restart if the VBUS UVLO

cycles low and then high (e.g., VBUS is removed and then

replaced) or if the charger is momentarily disabled using

the D2 pin.

Charge Current

The charge current is programmed using a single resistor

from PROG to ground. 1/1030th of the battery charge cur-

rent is delivered to PROG, which will attempt to servo to

1.000V. Thus, the battery charge current will try to reach

1030 times the current in the PROG pin. The program

resistor and the charge current are calculated using the

following equations:

PROG

CHG

PROG

1030

In either the constant-current or constant-voltage charging

modes, the voltage at the PROG pin will be proportional

to the actual charge current delivered to the battery. The

charge current can be determined at any time by monitoring

the PROG pin voltage and using the following equation:

BAT

PROG

• 1030

In many cases, the actual battery charge current, IBAT, will

be lower than the programmed current, ICHG, due to limited

input power available and prioritization to the system load

drawn from VOUT.

Charge Status Indication

The CHRG pin indicates the status of the battery charger.

Four possible states are represented byCHRG which include

charging, not charging (or ﬂoat charge current less than

programmed end of charge indication current), unrespon-

sive battery and battery temperature out of range.

The signal at the CHRG pin can be easily recognized as

one of the above four states by either a human or a mi-

croprocessor. An open-drain output, the CHRG pin can

drive an indicator LED through a current limiting resistor

for human interfacing or simply a pull-up resistor for

microprocessor interfacing.

OPERATION

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