MCP73811 datasheet(13/22 Pages) MICROCHIP

13 / 22 page

DS22036A-page 13

MCP73811/2

6.0

APPLICATIONS

The MCP73811/2 is designed to operate in conjunction

with a host microcontroller or in stand-alone

applications. The MCP73811/2 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

(180 mAh Battery).

FIGURE 6-3:

Typical Charge Profile in

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

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

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.

VDD

VSS

PROG

VBAT

Single

Li-Ion

Cell

MCP73812

CIN

Li-Ion Battery Charger

RPROG

COUT

REGULATED

WALL CUBE

0.0

1.0

2.0

3.0

4.0

5.0

6.0

Time (s)

100

120

MCP73812/IOT

VDD = 5.2V

RPROG = 10 kΩ

0.0

1.0

2.0

3.0

4.0

5.0

6.0

Time (s)

100

200

300

400

500

600

MCP738312

VDD = 5.2V

RPROG = 2 kΩ

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