TC3827 View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

TC3827

Lithium-Ion Battery Charger

Microchip Technology 

Lithium-Ion Battery Charger

TC3827

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-

ponents are a PMOS , two small capacitors, and an RSENSE.

The charge current profile can be monitored using the

voltage signal at IMON. The use of an LED as a status

indicator is optional. The application circuit is shown in

Figure 1.

VOUT

VREG

IREG

Constant

Voltage

Mode

Foldback

Current

Limited

Mode

ISC

VIN

IMAX

IFOLDBACK

IOUT

NDP6020P

R

=500mΩ

SENSE

PMOS

10µF

S

D

G

VIN

MODE

IMON

SHDN

VSNS VDRV

VOUT

TC3827

GND

22µF

VOUT

Figure 2. TC3827 Charging Characteristic

SELECTING EXTERNAL COMPONENTS

Figure 3. TC3827 Test Circuit

CHARGER MODES DESCRIPTION

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

(VGSTH), drain current and power-dissipation capabilities.

Bypass Capacitors

Bypass VIN with a capacitor value of at least 10µF.

Bypass VOUT with a capacitor value of at least 1µF.

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

resistor sets IMAX. The voltage drop across the current sense

resistor is applied to the VIN -VSNS pins and presented to the

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

TC3827-2 12/12/00

4

© 2001 Microchip Technology Inc. DS21558A

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