1

LT1507

500kHz Monolithic

Buck Mode Switching Regulator

5V to 3.3V Efficiency

LOAD CURRENT (A)

0

100

90

80

70

60

50

1.00

LT1507 • TA02

0.25

0.50

0.75

1.25

5V to 3.3V Volt Down Converter

SHDN

SENSE

BOOST

GND

LT1507-3.3

D2

†

1N914

C2

0.1

µF

L1***

5

µH

D1

1N5818

3.3nF

+

C1**

100

µF

10V

TANTALUM

OUTPUT

3.3V

1.25A

DEFAULT

(OPEN)

= ON

+

C3*

47

µF

16V

TANTALUM

5V

*

**

***

†

AVX TPSD477M016R0150 OR SPRAGUE 593D EQUIVALENT.

RIPPLE CURRENT RATING

≥ 0.6A

AVX TPSD108M010R0100 OR SPRAGUE 593D EQUIVALENT

COILTRONICS CTX5-1. SUBSTITUTION UNITS SHOULD BE RATED

AT

≥ 1.25A, USING LOW LOSS CORE MATERIAL

SEE BOOST PIN CONSIDERATIONS IN APPLICATIONS INFORMATION

SECTION FOR ALTERNATIVE D2 CONNECTION

with all the necessary oscillator, control and logic cir-

cuitry. High switching frequency allows a considerable

reduction in the size of external components. The topology

is current mode for fast transient response and good loop

stability. Both fixed output voltage (3.3V) and adjustable

parts are available.

A special high speed bipolar process and new design

techniques allow this regulator to achieve high efficiency

at a high switching frequency. Efficiency is maintained

over a wide output current range by keeping quiescent

supply current to 4mA and by utilizing a supply boost

capacitor to allow the NPN power switch to saturate. A

shutdown signal will reduce supply current to 20

µA. The

LT1507 can be externally synchronized from 570kHz to

1MHz with logic level inputs.

The LT1507 fits into standard 8-pin SO and PDIP pack-

ages. Temperature rise is kept to a minimum by the high

efficiency design. Full cycle-by-cycle short-circuit protec-

tion and thermal shutdown are provided. Standard surface

mount external parts are used including the inductor and

capacitors.

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

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Portable Computers

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Battery-Powered Systems

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Battery Charger

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Distributed Power

FEATURES

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Constant 500kHz Switching Frequency

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Uses All Surface Mount Components

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Operates with Inputs as Low as 4V

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Saturated Switch Design (0.3

Ω)

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Cycle-by-Cycle Current Limiting

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Easily Synchronizable

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Inductor Size as Low as 2

µH

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Shutdown Current: 20

µA

The LT

regulator, functionally identical to the LT1375 but opti-

mized for lower input voltage applications. It will operate

over a 4V to 15V input range, compared with 5.5V to 25V

for the LT1375. A 1.5A switch is included on the die along