4

Lithium-Ion Battery Charger

TC3827

TC3827-2 12/12/00

© 2001 Microchip Technology Inc.

DS21558A

APPLICATIONS INFORMATION

A typical Li-Ion cell should be charged at a controlled

current until it reaches 4.1V or 4.2V (depending on the type

of cell), then charged at this voltage. The TC3827 is de-

signed to offer the maximum integration and function with a

small application circuit. The only necessary external com-

The charge current profile can be monitored using the

indicator is optional. The application circuit is shown in

Figure 1.

SELECTING EXTERNAL COMPONENTS

Power Supply Input

In most applications, this will be a small “wall cube”

switching converter with an output voltage limit range of 5V

to 6V.

P-Channel Pass Device

The PMOS is used to regulate current from the source

into the Li-Ion cell. Specifications to consider when choosing

an appropriate PMOS are the minimum drain-source break-

down voltage, the minimum turn-on threshold voltage

Bypass Capacitors

CHARGER MODES DESCRIPTION

Initiating a Charge Cycle

The TC3827 initiates a charge upon toggling the shut-

down pin high, insertion of the battery or application of an

external power source. The TC3827 provides a foldback

current limited charge where an external current sense

current limited control-loop.The current loop will protect a

deeply discharged (or shorted) battery by folding back the

current limited charge, and reduces the power dissipation in

PMOS.

Current Limited, Constant-voltage Charge

Cycle

The TC3827 begins to charge the Li-Ion cell by turning

on the external PMOS. The charge continues until the

battery voltage rises to the lithium-ion cell voltage of 4.2V or

4.1V (depending on type of cell). As the battery voltage

reaches the regulated output voltage, the internal feedback

Figure 3. TC3827 Test Circuit

V

REG

V

OUT

I

REG

I

MAX

I

FOLDBACK

Constant

Voltage

Mode

Foldback

Current

Limited

Mode

I

SC

I

OUT

Figure 2. TC3827 Charging Characteristic

R

SENSE

=500m

Ω

S

G

D

NDP6020P

PMOS

V

SNS

V

DRV

GND

V

IN

V

IN

V

OUT

V

OUT

SHDN

MODE

10

µF

TC3827

22

µF