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© 2007 Microchip Technology Inc. DS22036B-page 13
MCP73811/2
6.0 APPLICATIONS
The MCP73811/2 is designed to operate in conjunction
with a host microcontroller or in stand-alone
applications. The MCP73811/2 provides the preferred
charge algorithm for Lithium-Ion and Lithium-Polymer
cells Constant-current followed by Constant-voltage.
Figure 6-1 depicts a typical stand-alone application
circuit, while Figures 6-2 depict the accompanying
charge profile.
FIGURE 6-1: Typical Application Circuit.
FIGURE 6-2: Typical Charge Profile
(950 mAh Li-Ion Battery).
6.1 Application Circuit Design
Due to the low efficiency of linear charging, the most
important factors are thermal design and cost, which
are a direct function of the input voltage, output current
and thermal impedance between the battery charger
and the ambient cooling air. The worst-case situation is
when the device has transitioned from the
Preconditioning mode to the Constant-current mode. In
this situation, the battery charger has to dissipate the
maximum power. A trade-off must be made between
the charge current, cost and thermal requirements of
the charger.
6.1.1 COMPONENT SELECTION
Selection of the external components in Figure 6-1 is
crucial to the integrity and reliability of the charging
system. The following discussion is intended as a guide
for the component selection process.
6.1.1.1 Charge Current
The preferred fast charge current for Lithium-Ion cells
is at the 1C rate, with an absolute maximum current at
the 2C rate. For example, a 500 mAh battery pack has
a preferred fast charge current of 500 mA. Charging at
this rate provides the shortest charge cycle times
without degradation to the battery pack performance or
life.
CE
V
DD
V
SS
PROG
V
BAT
+
-
Single
Li-Ion
Cell
4
MCP73812
5
3
1
C
IN
Li-Ion Battery Charger
2
R
PROG
C
OUT
REGULATED
WALL CUBE