Datasheet

© 2009 Microchip Technology Inc. DS22005B-page 19
MCP73833/4
6.0 APPLICATIONS
The MCP73833/4 is designed to operate in conjunction
with a host microcontroller or in stand-alone
applications. The MCP73833/4 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 and 6-3 depict the
accompanying charge profile.
FIGURE 6-1: Typical Application Circuit.
FIGURE 6-2: Typical Charge Profile with
Thermal Regulation (1700 mAh Li-Ion Battery).
FIGURE 6-3: Typical Charge Cycle Start
with Thermal Regulation (1700 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 scenario 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 Current Programming Resistor
(R
PROG
)
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.
STAT1
V
DD
V
SS
PROG
V
BAT
+
-
Single
Li-Ion
Cell
1,2
MCP73833
6
9,10
7
Li-Ion Battery Charger
5
STAT2
PG
THERM
4
38
C
IN
Regulated
Wall Cube
R
PROG
R
LED
C
OUT
LED
R
LED
R
LED
LED LED
R
T1
10 kΩT
R
T2
0.0
1.0
2.0
3.0
4.0
5.0
0
20 40 60 80
100 120 140 160
Time (Minutes)
Battery Voltage (V)
0.00
0.40
0.80
1.20
1.60
2.00
Charge Current (A)
MCP73833-FCI/MF
V
DD
= 5.2V
R
PROG
= 1.00 k:
0.0
1.0
2.0
3.0
4.0
5.0
0 2 4 6 8
10
Time (Minutes)
Battery Voltage (V)
0.00
0.40
0.80
1.20
1.60
2.00
Charge Current (A)
MCP73833-FCI/MF
V
DD
= 5.2V
R
PROG
= 1.00 k: