MCP73837AMIMF datasheet(20/30 Pages) MICROCHIP

20 / 30 page

MCP73837/8

DS22071A-page 20

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.

FIGURE 6-1:

MCP73837 Typical Stand-Alone Application Circuit.

FIGURE 6-2:

Typical Charge Profile

(1200 mAh Li-Ion Battery).

FIGURE 6-3:

Typical Charge Profile in

Thermal Regulation (1200 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 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

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.

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:

STAT1

/PG

BAT

Single

Li-Ion

Cell

MCP73837

STAT2

THERM

USB

PROG1

PROG2

USB Port

Low

Thermsitor

PROG

ΚΩ

REGULATED

WALL CUBE

IN1

IN2

OUT

0.0

1.0

2.0

3.0

4.0

5.0

Time (Minutes)

0.2

0.4

0.6

0.8

1.2

VDD = 5.2V

RPROG = 1 kΩ

1200 mAh Li-Ion Battery

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0123456789

Time (Minutes)

0.3

0.6

0.9

1.2

VDD = 5.2V

RPROG = 1 kΩ

1200 mAh Li-Ion Battery

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