LTC3552

1

3552f

Standalone Linear Li-Ion

Battery Charger and Dual

Synchronous Buck Converter

voltage linear charger with a dual DC/DC converter for

single cell lithium-ion batteries. Its DFN package and low

external component count make the LTC3552 ideally suited

for portable applications. Furthermore, the LTC3552 is

designed to work within USB power specifications.

No external sense resistor or external blocking diode is

required due to the internal MOSFET architecture. The

charge voltage is fixed at 4.2V and the charge current is

programmed with a resistor. The charge cycle terminates

when the charge current drops below the programmed

termination threshold after the final float voltage is reached.

When the input supply (wall adapter or USB supply) is

removed, the LTC3552 enters a low current state dropping

the battery drain current to less than 2µA. Thermal regula-

tion maximizes charge rate without risk of overheating.

The synchronous step-down switching regulators gen-

erate adjustable output voltages from 5V down to 0.6V.

The switching frequency is set at 2.25MHz, allowing the

use of small surface mount inductors and capacitors.

■

Cellular Telephones, PDAs, MP3 Players

■

Bluetooth Applications

■

Programmable Charge Current Up to 950mA

■

Complete Linear Charger and Dual DC/DC

Regulator

■

Buck Converter Output Voltage from 0.6V to 5V

■

No MOSFET, Sense Resistor or Blocking Diode

Required

■

Thermal Regulation Maximizes Charge Rate

Without Risk of Overheating*

■

Charges Directly from a USB Port

■

Programmable Charge Current Termination

■

Preset 4.2V Charge Voltage with ±1% Accuracy

■

Charge Current Monitor Output for Gas Gauging*

■

Automatic Recharge

■

Charge Status Output

■

“Power Present” Output

■

2.9V Trickle Charge Threshold

■

Soft-Start Limits Inrush Current

■

Low Quiescent Current Buck Converter (40µA)

■

Current Mode Operation, Constant Frequency (2.25MHz)

■

Low Profile (5mm × 3mm × 0.75mm) DFN Package

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

*Protected by U.S. patents, including 6522118, 6700364, 5481178, 6580258, 6304066,

6127815, 6498466, 6611131.

Single Cell Li-Ion Battery Charger with

C/5 Termination and Dual DC/DC Converter

LOAD CURRENT (mA)

1

100

95

90

85

80

75

70

65

60

1000

100

10

1

0.1

10

100

1000

3552 TA01b

Burst Mode OPERATION

REGULATOR 1, NO LOAD ON REGULATOR 2

POWER LOSS

EFFICIENCY

Efficiency Curve/

Power Loss of Regulators

4.5V TO

6.5V

2.5V/

400mA

1.8V/

800mA

3552 TA01

LTC3552

GND

4.7

µF

CER

10

µF

CER

ITERM

PROG

SW2

RUN1

RUN2

BAT

SW1

800mA

68pF

R4

887k

R3

280k

33pF

4.7

µH

1

µF

10

µF

2.2

µH

CHRG

PWR

EN

619

Ω

1.24k

+

4.2V

1-CELL

Li-Ion

BATTERY

R2

604k

R1

301k

POR

MODE/SYNC