LTC3521



3521f

Typical applicaTion

FeaTures

applicaTions

DescripTion

DC/DC and Dual 600mA

Buck DC/DC Converters

anddual600mAsynchronousbuckDC/DCconverters.The

1.1MHz switching frequency minimizes the solution foot-

printwhilemaintaininghighefficiency.Allthreeconverters

feature soft-start and internal compensation to minimize

the solution footprint and simplify the design process.

The buck converters are current mode controlled and

utilize an internal synchronous rectifier to improve ef-

ficiency. The buck converters support 100% duty cycle

operation to extend battery life. If the PWM pin is held

low, the buck converters automatically transition from

Burst Mode operation to PWM mode at high loads. With

the PWM pin held high, the buck converters remain in low

noise, 1.1MHz PWM mode.

Thebuck-boostconverterfeaturescontinuousconduction

operation to maximize efficiency and minimize noise. At

light loads, the buck-boost converter can be operated in

Burst Mode operation to improve efficiency and reduce

no-load standby current.

The LTC3521 provides a <2μA shutdown mode, over-

temperature shutdown and current limit protection

on all converters. The LTC3521 is available in a 24-pin

0.75mm

× 4mm × 4mm QFN package, and a 20-pin

thermally enhanced TSSOP package.

n

Three High Efficiency DC/DC Converters:

n

1.8V to 5.5V Input Voltage Range

n

n

30µA Total Quiescent Current in Burst Mode

Operation

n

Independent Power Good Indicator Outputs

n

Integrated Soft-Start

n

Thermal and Overcurrent Protection

n

<2µA Current in Shutdown

n

Small 4mm

× 4mm QFN and Thermally Enhanced

TSSOP Packages

n

Bar Code Readers

n

Medical Instruments

n

Handy Terminals

n

PDAs, Handheld PCs

n

GPS Receivers

+

SW2

SW3

FB2

FB3

LTC3521

SHDN2

SHDN1

1.0M

137k

68.1k

10µF

Li-Ion

3.3V

800mA

1.8V

600mA

100k

100k

10µF

1.2V

600mA

2.4V TO 4.2V

221k

3521 TA01a

SHDN3

PWM

SW1A

SW1B

FB1

PGOOD2

PGOOD1

PGOOD3

PGND2

GND

PGND1

ON

OFF

PWM

BURST

2.4

92

94

96

98

5.4

3521 TA01b

88

90

86

84

82

80

76

78

74

72

70

3.4

4.4

100

L

, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks

and PowerPath is a trademark of Linear Technology Corporation. All other trademarks are the

property of their respective owners. Protected by U. S. Patents, including 6404251, 6166527.