LP3918 Datasheet, PDF (19/30 Pages) National Semiconductor (TI) – Battery Charge Management and Regulator Unit

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 pro-
grammable battery regulation voltage and end of charge cur-
rent 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
(V_TERM) 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 mainte-
nance 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 termi-
nation 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 pro-
grammed to 19 levels from 50mA to 950mA. These values
are given in Table 5, and Table 12
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 9
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.
20211638
FIGURE 1. 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.
Programming Information
TABLE 10. Register Address 8h'10: CHGCNTL1
BIT
NAME
FUNCTION
2
En_EOC Enables the End Of Charge current
level threshold detection. When set
to '0' the EOC is disabled.
The End Of Charge current threshold default setting is at
0.1C. This EOC value is set relative to C the set full rate con-
stant current. This threshold can be set to 0.1C, 0.15C, 0.2C
or 0.25C bychanging the contents of the PROG_EOC[1:0]
register bits.
TABLE 11. Register Address 8h'12: CHGCNTL3
BIT
NAME
FUNCTION
2 Prog_EOC[0] Set the End Of Charge Current.
3 Prog_EOC[1] ^{See Table 9}
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