1

LT1533

Ultralow Noise

1A Switching Regulator

FEATURES

The LT

to reduce conducted and radiated electromagnetic interfer-

ence (EMI). Ultralow noise and EMI are achieved by providing

user control of the output switch slew rates. Voltage and

current slew rates can be independently programmed to

optimize switcher harmonic content versus efficiency. The

LT1533 can reduce high frequency harmonic power by as

much as 40dB with only minor losses in efficiency.

The LT1533 utilizes a dual output switch current mode

architecture optimized for low noise topologies. The IC

includes two 1A power switches along with all necessary

oscillator, control and protection circuitry. Unique error amp

circuitry can regulate both positive and negative voltages.

The internal oscillator may be synchronized to an external

clock for more accurate placement of switching harmonics.

Protection features include cycle by cycle current limit pro-

tection, undervoltage lockout and thermal shutdown.

Low minimum supply voltage and low supply current during

shutdown make the LT1533 well suited for portable applica-

tions. The part may also be forced into a 50% duty cycle mode

for unregulated applications. The LT1533 is available in the

16-pin narrow SO package.

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Greatly Reduced Conducted and Radiated EMI

(<100

s

Low Switching Harmonic Content

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Independent Control of Switch Voltage and

Current Slew Rates

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Two 1A Current Limited Power Switches

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Regulates Positive and Negative Voltages

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20kHz to 250kHz Oscillator Frequency

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Easily Synchronized to External Clock

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Wide Input Voltage Range: 2.7V to 23V

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Low Shutdown Current: 12

µA Typical

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Easier Layout than with Conventional Switchers

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Outputs Can Be Forced to 50% Duty Cycle for

Unregulated Applications

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Precision Instrumentation Systems

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Isolated Supplies for Industrial Automation

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Medical Instruments

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Wireless Communications

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Single Board Data Acquisition Systems

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

SHDN

DUTY

SYNC

COL A

COL B

PGND

FB

NFB

LT1533

GND

5V

14

2

15

16

13

12

7

11

3

4

5

6

10

820pF

16.9k

0.015

µF

1000pF

15k

Note 1

33

µF

15k

15k

+

T1

1N4148

B

A

L1

300

µH

L2

33

µH

1N4148

2.49k

1%

8

9

21.5k, 1%

C1

47

µF

16V

+

C2

33

µF

20V

C1: SANYO OS-CON

C2: AVX TPS TANTALUM

L1: COILTRONICS CTX300-2

L2: COILCRAFT DT1608C-333

T1: COILTRONICS CTX02-13834

NOTE 1: 25nH TRACE INDUCTANCE

OR COILCRAFT B07T

12V

150mA

1533 TA01

+

Low Noise 5V to 12V Forward Push-Pull DC/DC Converter

B

2mV/DIV

A

100

µV/DIV

2

µs/DIV

1533 TA02

12V Output Noise (BW = 100MHz)

<100