NE57600 Philipss, NE57600 Datasheet - Page 7

• Manufacturer Part Number: NE57600
• Description: One-cell Lithium-ion battery protection with over/undercharge and overcurrent protection
• Manufacturer: Philipss

Philips Semiconductors
Charging Lithium Cells
The lithium cells must be charged with a dedicated charging IC such
as the NE57600. These dedicated charging ICs perform a
current-limited, constant-voltage charge, as shown in Figure 7.
The charger IC begins charging with a current that is typically the
rating of the cell (1C) or the milliampere rating of the cell. As the cell
approaches its full-charge voltage rating (V
the cell decreases, and the charger IC provides a constant voltage.
When the charge current falls below a preset amount, 50 mA for
example, the charge is discontinued.
If charging is begun below the overdischarged voltage rating of the
cell, it is important to slowly raise the cell voltage up to this
overdischarged voltage level. This is done by a reconditioning
charge. A small amount of current is provided to the cell (50 mA for
example), and the cell voltage is allowed a period of time to rise to
the overdischarged voltage. If the cell voltage recovers, then a
normal charging sequence can begin. If the cell does not reach the
overdischarged voltage level, then the cell is too damaged to charge
and the charge is discontinued.
To take advantage of the larger energy density of lithium cells it is
important to allow enough time to completely charge the cell . When
the charger switches from constant current to constant voltage
charge (Point B, Figure 7) the cell only contains about 80 percent of
its full capacity. When the cell is 100 mV less than its full rated
charge voltage the capacity contained within the cell is 95 percent.
Hence, allowing the cell to slowly complete its charge takes
advantage of the larger capacity of the lithium cells.
2001 Oct 03
One-cell Lithium-ion battery protection with
over/undercharge and overcurrent protection
OV
), the current entering
7
1.0
0.5
4.0
3.0
Vov
Figure 7. Lithium cell charging curves.
CONSTANT
CURRENT
TIME (HOURS)
TIME (HOURS)
1.0
1.0
Point B
CONSTANT
VOLTAGE
NE57600
2.0
2.0
Product data
SL01554