MCP73838G8IMF View Datasheet(PDF) - Microchip Technology
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MCP73838G8IMF Datasheet PDF : 30 Pages
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MCP73837/8
6.0 APPLICATIONS
The MCP73837/8 devices are designed to operate in
conjunction with a host microcontroller or in stand-
alone applications. The MCP73837/8 devices provide
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 MCP73837 application circuit, while Figure 6-2
and Figure 6-3 depict the accompanying charge
profile.
CIN1
REGULATED
WALL CUBE
USB Port
CIN2
1 ΚΩ
1 ΚΩ
1 ΚΩ
1
VAC
2 VUSB
3
STAT1
4 STAT2
8 /PG
VBAT
THERM
10
Thermsitor
9
COUT
VSS 5
PROG2 7
PROG1 6
Low Hi
MCP73837
RPROG
Single
Li-Ion
Cell
FIGURE 6-1:
MCP73837 Typical Stand-Alone Application Circuit.
5.0
1.2
4.0
1
0.8
3.0
0.6
2.0
0.4
1.0
VDD = 5.2V
RPROG = 1 kΩ
0.2
1200 mAh Li-Ion Battery
0.0
0
Time (Minutes)
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.
FIGURE 6-2:
Typical Charge Profile
(1200 mAh Li-Ion Battery).
4.5
1.2
4.0
3.5
0.9
3.0
2.5
0.6
2.0
1.5
1.0
VDD = 5.2V
RPROG = 1 kΩ
0.3
0.5 1200 mAh Li-Ion Battery
0.0
0
0 1 2 3 4 5 6 7 8 9 10
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
should always follow references and guidance from
battery manufacturers. For example, programming
700 mA fast charge current for a 1000 mAh Li-Ion
battery pack if its preferred fast charge rate is 0.7C.
This will result the shortest charge cycle time without
degradation a battery's life and performance.
Time (Minutes)
FIGURE 6-3:
Typical Charge Profile in
Thermal Regulation (1200 mAh Li-Ion Battery).
6.1.1.2 Thermal Considerations
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:
DS22071A-page 20
© 2007 Microchip Technology Inc.
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