Datasheet

 2011-2013 Microchip Technology Inc. DS20005049C-page 17
MCP73830/L
6.0 APPLICATIONS
The MCP73830 is designed to operate in conjunction
with a host microcontroller or in stand-alone applica-
tions. The MCP73830/L provides the preferred charge
algorithm for dual Lithium-Ion or Lithium-Polymer cell’s
constant current, followed by constant voltage.
Figure 6-1 depicts a typical stand-alone application
circuit, while Figure 6-2 depicts the accompanying
charge profile.
FIGURE 6-1: Typical Application Circuit.
FIGURE 6-2: Typical Charge Profile
(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 Preconditioning
mode to 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 Li-Ion/Li-Poly cells
is below the 1C rate, with an absolute maximum current
at the 2C rate. The recommended fast charge
current should be obtained from the battery
manufacturer. For example, a 500 mAh battery pack
with 0.7C preferred fast charge current has a charge
current of 350 mA. Charging at this rate provides the
shortest charge cycle times without degradation to the
battery pack performance or life.
6.1.1.2 Thermal Considerations
The worst-case power dissipation in the battery char-
ger occurs when the input voltage is at the maximum
and the device has transitioned from Preconditioning
mode to Constant Current mode. In this case, the
power dissipation is:
EQUATION 6-1:
STAT
V
DD
V
BAT
3
4
PROG
1
2
6
Regulated
wall cube
4.7µF
2k
+
-
1-Cell
Li-Ion
Battery
V
SS
5
4.7 µF
1k
CE
Hi
Lo
MCP73830/L
Note: Please consult with your battery supplier,
or refer to the battery data sheet, for the
preferred charge rate.
PowerDissipation V
DDMAX
V
PTHMIN
–I
REGMAX
 =
Where:
V
DDMAX
= the maximum input voltage
I
REGMAX
= the maximum fast charge current
V
PTHMIN
= the minimum transition threshold
voltage