LP3921

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SNVS580A – AUGUST 2008 – REVISED MAY 2013

Table 6. Charging Termination Voltage Control

VTERM[1]

VTERM[0]

Termination Voltage (V)

0

0

4.1

0

1

4.2 (Default)

1

0

4.3

1

1

4.4

PROG_EOC[1]

PROG_EOC[0]

End of Charge Current

0

0

0.1 (Default)

0

1

0.15C

1

0

0.2C

1

1

0.25C

(1)

Note: C is the set charge current.

Table 8. Charging Restart Voltage Programming

PROG_VRSTRT[1]

PROG_VRSTRT[1]

Restart Voltage(V)

0

0

0

1

1

0

1

1

Table 9. USB Charging Selection

USB_Mode_En

CHG_Mode_En

Mode

Current

0

0

Fast Charge

Default or Selection

1

0

Fast Charge

Default or Selection

0

1

USB

100 mA

1

1

USB

450 mA

Battery Charge Management

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

the LP3921. 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 50 mA is available to charge the battery to 3.0V. At this voltage level the charge

management applies the default (100 mA) 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.

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 10.

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

values are given in Table 5 and Table 13.

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