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DC/DC converters with automatic PFM-PWM mode operation

Posted: 27 Jan 2005 ?? ?Print Version ?Bookmark and Share

Keywords:national semiconductor? DC/DC converter? portable system? lm3670?

National Semiconductor Corp. unveiled the first two products in a family of miniature, high efficiency synchronous step-down DC/DC converters for portable systems. According to the company, its new LM3670 and LM3671 optimize the efficiency and size of portable devices, including wireless handsets, digital still cameras, MP3 players, PDAs, hard disk drives, wireless LAN and other low-power, small form-factor products.

Both the LM3670 and LM3671 feature automatic PFM-PWM (pulse frequency modulationpulse width modulation) mode operation, which delivers one of the highest efficiency over the entire load. The synchronous rectification attribute of the DC/DC converters achieves up to 95 percent efficiency during continuous switching operation.

In addition, these devices feature a quiescent current of 16?A (typ.) and generate less than 5mV peak-to-peak output voltage ripple, making them suitable for RF-based portable systems. The small 2.2?H inductor, 10?F output capacitors and SOT-23 package minimize the footprint size, added National.

"Today's feature-rich portable electronics need more efficient power management to maintain peak performance at all power levels," shared Peter Henry, the company's VP for its Portable Power Products Group. "The LM3670 and LM3671 accomplish this by combining a tiny solution size with the highest efficiency and longest stand-by times to offer the most effective buck regulator solution for portable power solutions."

The LM3671 DC/DC converter has a load capability of up to 600mA, and powers low-voltage circuits operating from a Li-ion battery or 2.8V to 5.5V voltage rails. Its 2MHz oscillator frequency enables the use of three very small external components for operation, including a 2.2?H inductor and two 10?F capacitors. The LM3671's high-output voltage accuracy, low-output voltage ripple and fast transient response enable peak processor MIPS.

According to the press release, the LM3671 offers superior features and performance for powering digital cores and peripherals in portable systems. Automatic switching between PWM low-noise and PFM low-current modes lead to high-efficiency performance over the complete load range. At the same time, fixed-frequency PWM mode drives loads from approximately 70mA to 600mA while the PFM mode takes over at lower loads. In shutdown mode (enable pin pulled low), the device turns off and reduces battery consumption to 0.1?A typically. The LM3671 is available in the following output voltage options: 3.3-, 1.875-, 1.8-, 1.6-, 1.5-, 1.375-, 1.25- and 1.2V, as well as an adjustable option for other voltages.

Meanwhile, the LM3670 is the low-power version of the LM3671 and is optimized for systems and applications with lower output current requirements. It switches at 1MHz and has a load capability of up to 300mA. This product requires a small 10?H inductor and two 4.7?F capacitors for operation. It is available in the following output voltage options: 1.8-, 1.875- and 1.5V, and an adjustable option for other voltages.

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