MCP73831/2
cells constant current followed by constant voltage.
Figure 6-1 depicts a typical stand-alone application
circuit, while Figures 6-2 and 6-3 depict the
accompanying charge profile.
6.0
APPLICATIONS
The MCP73831/2 are designed to operate in conjunc-
tion with a host microcontroller or in a stand-alone
application. The MCP73831/2 provide the preferred
charge algorithm for Lithium-Ion and Lithium-Polymer
Li-Ion Battery Charger
4
3
5
2
VDD
VBAT
+
-
Single
Li-Ion
Cell
CIN
RLED
LED
COUT
STAT PROG
REGULATED
WALL CUBE
RPROG
1
VSS
MCP73831
FIGURE 6-1:
Typical Application Circuit.
6.0
5.0
4.0
3.0
2.0
120
100
80
6.0
5.0
4.0
3.0
2.0
1.0
0.0
600
500
400
300
200
100
0
60
40
MCP73831-2AC/IOT
VDD = 5.2V
RPROG = 10 kΩ
MCP73831-2AC/IOT
VDD = 5.2V
RPROG = 2 kΩ
1.0
0.0
20
0
Time (minutes)
Time (minutes)
FIGURE 6-2:
Typical Charge Profile
FIGURE 6-3:
Typical Charge Profile in
(180 mAh Battery).
Thermal Regulation (1000 mAh 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.
6.1.1.1
Current Programming Resistor
(RPROG
)
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.
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.
© 2006 Microchip Technology Inc.
DS21984B-page 13