MCP73831 Microchip Technology, Inc., MCP73831 Datasheet - Page 13

• Manufacturer Part Number: MCP73831
• Manufacturer: Microchip Technology, Inc.

6.0
The MCP73831 is designed to operate in conjunction
with a host microcontroller or in a stand-alone applica-
tion. The MCP73831 provides the preferred charge
algorithm for Lithium-Ion and Lithium-Polymer cells
FIGURE 6-1:
FIGURE 6-2:
(180 mAh Battery).
6.1
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
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
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.
© 2005 Microchip Technology Inc.
6.0
5.0
4.0
3.0
2.0
1.0
0.0
the
APPLICATIONS
Application Circuit Design
COMPONENT SELECTION
MCP73831-2AC/IOT
V
R
device
DD
PROG
REGULATED
WALL CUBE
= 5.2V
= 10k
Typical Application Circuit.
Typical Charge Profile
has
Time (S)
transitioned
C
IN
from
120
100
80
60
40
20
0
R
LED
LED
the
Li-Ion Battery Charger
4
1
V
STAT
DD
MCP73831
constant current followed by constant voltage.
Figure 6-1 depicts a typical stand-alone application
circuit,
accompanying charge profile.
FIGURE 6-3:
Thermal Regulation (1000 mAh Battery).
6.1.1.1
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.
6.1.1.2
The worst-case power dissipation in the battery
charger occurs when the input voltage is at the
maximum and the device has transitioned from the
Preconditioning mode to the Constant-Current mode.
In this case, the power dissipation is:
PROG
V
6.0
5.0
4.0
3.0
2.0
1.0
0.0
V
BAT
SS
while
MCP73831-2AC/IOT
V
R
DD
PROG
3
5
2
Current Programming Resistor
(R
Thermal Considerations
= 5.2V
= 2k
PROG
Figures 6-2
R
C
)
PROG
Typical Charge Profile in
OUT
Time (S)
MCP73831
and 6-3
+
-
Single
Li-Ion
Cell
DS21984A-page 13
depict
600
500
400
300
200
100
0
the