LM3351

Switched Capacitor Voltage Converter

General Description

The LM3351 is a CMOS charge-pump voltage converter

which efficiently provides a 3.3V to 5V step-up, or 5V to 3.3V

step-down. The LM3351 is pin for pin compatible with the

LM3350 but consumes 66% less quiescent current. The

LM3351 uses four small, low cost capacitors to provide the

voltage conversion. It eliminates the cost, size and radiated

EMI related to inductor based circuits, or the power loss of a

linear regulator. Operating power conversion efficiency

greater than 90% provides ideal performance for battery

powered portable systems.

The architecture provides a fixed voltage conversion ratio of

3/2 or 2/3. Thus it can be used for other DC-DC conversions

as well.

Key Specifications

n 200 kHz switch frequency allows use of very small,

inexpensive capacitors.

n 4.2

Ω typical step-up output impedance

n 1.8

Ω typical step-down output impedance

n 95% typical power conversion efficiency at 50 mA

n 250 nA typical shutdown current

n Low quiescent current extends battary life

Features

n Conversion of 3.3V to 5V, or 5V to 3.3V

n Small Mini SO-8 package

n No inductor required

Applications

n Any mixed 5V and 3.3V system

n Laptop computers and PDAs

n Handheld instrumentation

n PCMCIA cards

Ordering Information

Order Number

Package Type

NSC Package

Drawing

Package

Marking

Supplied As

LM3351MMX

Mini SO-8

MUA08A

S05A

3500 Units on Tape and Reel

LM3351MM

Mini SO-8

MUA08A

S05A

1000 Units on Tape and Reel

Basic Operating Circuits

Connection Diagram

Step-Up Converter

DS100146-1

Step-Down Converter

DS100146-2

Mini SO8 Package

DS100146-3

Top View

December 1999

© 1999 National Semiconductor Corporation

DS100146

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