Application Notes

LP3945 CHARGER OPERATION

The LP3945 is a complete battery charger with I

Charge cycle is initiated with wall adaptor insertion. If the

wall adaptor voltage appearing on the CHG-IN pin meets

under-voltage (V

the Adaptor OK signal is detected, then pre-conditioning

process begins (see Figure 1). In pre-qualification cycle, a

safe current level, less than 65 mA, is pumped into the

battery while the voltage across the battery terminals is

measured. Once this voltage exceeds 3.0V, the controller

will initiate constant current fast charge cycle. During this

cycle, the 5.6 hr safety timer is started and charge current is

increased to I

manufacturing to 500 mA but it is user programmable from

500 mA to 950 mA in 50 mA step. The programmed current

is determined by battery type and manufacturers’ recom-

mendation.

If safety timer times out during constant current cycle, charg-

ing will be terminated if StopModeEN pin is pulled high. If it

is pulled low, device will proceed to operate in maintenance

mode and have to be interrupted externally. This is not a

recommended mode of operation. Disabling the 5.6hr timer

can potentially expose the battery to prolong charge cycle

and damage the battery. If StopModeEN feature is used,

user must protect the battery from exposure to prolong

charge cycle.

As the battery is charged during constant current mode, the

voltage across pack terminal increases until it reaches 4.1V

(or 4.2V). As soon as pack terminal exceeds 4.1V (or 4.2V),

controller starts operating in constant voltage mode by ap-

plying regulated V

During this cycle, charge current, I

crease with time and when it drops below 0.1C (by default),

the EOC signal is activated indicating successful completion

of the charge cycle. The "C" term in 0.1C is the programmed

I

700mA is 140mA. EOC current can be programmed to 0.1C,

0.15C, or 0.2C. The default value is 0.1C. After completing

the full charge cycle, controller will start maintenance cycle

where battery pack voltage is monitored continuously. If

during the maintenance cycle, pack voltage drops below

3.9V, charge cycle will be initiated providing that the wall

adaptor is plugged in and is alive.

Ni-MH charge mode (LP3945 only), which is a constant

voltage mode charging, can be selected by setting the

“mode” bit to HIGH via the I

The LP3945 with I

ity in selecting charge current, battery regulation voltage

(4.1V or 4.2V), EOC current and battery type (Li Ion or

Ni-MH). The LP3945 operates in default mode during power

up. See the “I

LP3946 CHARGER OPERATION

The LP3946 is a simpler version of the LP3945. It does not

have any I

setting. The values in BOLD in Table 1 are the default

settings. Default settings can be set at the factory to custom-

er’s specifications. For other options, please contact a Na-

tional Semiconductor sales office.

The LP3946 charges only Li Ion type battery.

TABLE 1. LP3946 Performance Options

Battery Voltage

Regulation (V)

End of Charge Current

Threshold (mA)

Charge

Current (mA)

4.1

0.1C

500

4.2

0.15C

550

0.20C

600

650

700

750

800

850

900

950

20066510

FIGURE 1. Charger Power Up and Power Down Waveform

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