National Semiconductor Introduces the Industry’s First 50mA Fractional Voltage Switched Capacitor Converter in a Mini Small-Outline Package

New Device Converts 3.3V to 5V or 5V to 3.3V at 90%Efficiency

September 23, 1997 - National Semiconductor Corporation® today announced availability of a high-efficiency switched capacitor voltage converter designed for fractional step-up 3:2 conversion or step-down 2:3 conversion mode. The ratio is equivalent to the frequently required conversion of 5V to 3.3V or 3.3V to 5V. National’s LM3350 drives a 50mA load without the cost, size and radiated EMI related to inductor based circuits, or the power loss of a linear regulator. The LM3350 is a switched capacitor converter, requiring no external inductor. Housed in a mini SO-8 package, the IC is only 50% the size of the standard SO (small outline) package.

"The LM3350 voltage converter solves the power conversion problems inherent in a multiple-voltage system design," noted Venkatesh Shan, National's power management marketing manager. "The part’s unique architecture allows for the generation of the 3.3V or 5V needed to operate ICs such as ASICs, microcontrollers or sub-sections of systems used in battery-powered applications," he added.

The LM3350 switched capacitor converts supply voltages at a typical efficiency of 90%. A low output impedance of just 4.2 ohms limits the voltage droop to 0.3V at 50mA in step-up mode. An output impedance of 1.8 ohms limits the droop to 0.1V in the step-down mode. With an operating current of only 3.75 milliamps and operating efficiency greater than 90% at 50mA load, the device is ideal for a variety of battery-powered applications, such as notebook computers, PDAs, handheld instrumentation and PCMCIA cards.

The oscillator in the LM3350 has a typical frequency of 800kHz, allowing the use of very small, inexpensive 0.33 microfarad capacitors. The LM3350 also includes a low-current shutdown mode that disables the device and reduces the quiescent current to 25nA.

Although four low-cost capacitors are required to provide the output current, the LM3350 does not require an external inductor and does not generate high radiated EMI associated with inductor-based switchers, making it ideal for use in space-constrained portable designs.

Price and Availability
The LM3350MM (MSOP-8) is priced at $1.19 each in 1000-piece lots and is available now in production quantities.

For more information on the LM3350, visit our website at http://www.national.com/pf/LM/LM3350.html.

National Semiconductor Corporation, a Fortune 500 company, produces system on a chip silicon solutions for the information highway, based on its leadership in analog and mixed signal technologies. National is headquartered in Santa Clara, California, and focuses on the communications, personal systems and consumer markets. National has annual sales of approximately $2 billion and 12,500 employees worldwide. Additional company and product information is available on the World Wide Web at www.national.com.