VTERM

1.0A

I(Batt)

Constant Voltage

Current

Limiting

LP3918

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SNVS476D – AUGUST 2007 – REVISED MAY 2013

TECHNICAL DESCRIPTION

BATTERY CHARGE MANAGEMENT

A charge management system allowing the safe charge and maintenance of a Li-Ion battery is implemented on

the LP3918. This has a CC/CV linear charge capability with programmable battery regulation voltage and end of

charge current threshold. The charge current in the constant current mode is programmable and a maintenance

mode monitors for battery voltage drop to restart charging at a preset level. A USB charging mode is also

available with 2 charge current levels.

CHARGER FUNCTION

Following the correct detection of an input voltage at the charger pin the charger enters a pre-charge mode. In

this mode a constant current of 50mA is available to charge the battery to 3.0V. At this voltage level the charge

management applies the default (100mA) full rate constant current to raise the battery voltage to the termination

voltage level (default 4.2V). The full rate charge current may be programmed to a different level at this stage.

When termination voltage (VTERM) is reached, the charger is in constant voltage mode and a constant voltage of

4.2V is maintained. This mode is complete when the end of charge current (default 0.1C) is detected and the

charge management enters the maintenance mode. In maintenance mode the battery voltage is monitored for

the restart level (4.05V at the default settings) and the charge cycle is re-initiated to re-establish the termination

voltage level.

For start up the EOC function is disabled. This function should be enabled once start up is complete and a

battery has been detected. EOC is enabled via register CHGCNTL1, Table 9.

The full rate constant current rate of charge may be programmed to 19 levels from 50mA to 950mA. These

values are given in Table 4, and Table 11

The charge mode may be programmed to USB mode when the charger input is applied and the battery voltage is

above 3.0V. This provides two programmable current levels of 100mA and 450mA for a USB sourced supply

input at CHG_IN. Table 8

LDO Mode on device option LP3918TL-L

The charger circuit automatically enters an LDO mode if no battery is detected on insertion of the charger input

voltage. In LDO mode the battery pin is regulated to 4.2V and can source up to 1.0A of current. Normal operation

with a battery connected can be re-established via the serial interface. The serial interface allows the device to

switch between modes as required however care is required to ensure that LDO mode is not initiated while a

battery is present.

Figure 9. LDO Mode Diagram

EOC

EOC is disabled by default and should be enabled when the system processor is awake and the system detects

that a battery is present.

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