Miniature DC-DC Converters provide 95 Percent Efficiency

National Semiconductor Corporation introduces the first two products in a family of miniature, high efficiency synchronous step-down DC-DC converters for portable systems. The 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.

The LM3670 and LM3671 feature automatic PFM-PWM (pulse frequency modulation – pulse width modulation) mode operation which delivers the highest efficiency over the entire load. The synchronous rectification attribute of the LM3670 and LM3671 achieves up to 95 percent efficiency during continuous switching operation. These devices feature world-class quiescent current at 16 μA typical, resulting in excellent stand-by times that further extend battery life. The LM3670 and LM3671 have outstanding noise characteristics, generating less than 5 mV peak-to-peak output voltage ripple, making them ideal for RF-based portable systems. The small 2.2 μH inductor, 10 μF output capacitors and SOT-23 package minimize the footprint size.

“Today's feature-rich portable electronics need more efficient power management to maintain peak performance at all power levels,” said Peter Henry, vice president of National Semiconductor's 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.”

Key Technical Specifications of National's New LM3671 and LM3670
The LM3671 powers low-voltage circuits operating from a Lithium-Ion battery or 2.8 V to 5.5 V voltage rails. It has a load capability of up to 600 mA. The LM3671's 2 MHz oscillator frequency enables the use of three very small external components for operation, including a 2.2 μH inductor and two 10 μF capacitors. The LM3671's high-output voltage accuracy, low-output voltage ripple and fast transient response enable peak processor MIPS (million instructions per second). Exercise this performance in a design right now on National's WEBENCH online design tool at

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. Fixed-frequency PWM mode drives loads from approximately 70 mA to 600 mA while the PFM mode takes over at lower loads. PFM mode extends battery life through the reduction of quiescent current to typically 16 &muA under light loads and during system standby. In shutdown mode (enable pin pulled low), the device turns off and reduces battery consumption to 0.1 μA typically.

The LM3671 is available in the following output voltage options: 3.3 V, 1.875 V, 1.8 V, 1.6 V, 1.5 V, 1.375 V, 1.25 V, 1.2 V as well as an adjustable option for other voltages.

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 1 MHz and has a load capability of up to 300 mA. The LM3670 requires a very small 10 μH inductor and two 4.7 μF capacitors for operation. Try it out right now on National's WEBENCH online design tool at

The LM3670 is available in the following output voltage options: 1.8 V, 1.875 V, 1.5 V and an adjustable option for other voltages.

National Semiconductor is the number one supplier of power management ICs with 12.8 percent market share, according to iSuppli's 2004 voltage regulator/reference survey. National's power management revenue grew 29.7 percent in 2003 over the previous year, compared to 17.3 percent growth for the industry during the same time period. National's innovative power management products include best-in-class linear regulators; power monitoring, control and reference ICs; and switching converters, such as high-voltage ICs for DC/DC conversion, switched capacitor converters, lighting management ICs and inductive switching converters. National's WEBENCH online design tool allows designers to select a power management product, create and analyze a design, and then build custom prototypes that can be delivered within 24 hours.

More information about National's power management products is available at

Available now, the LM3670 is priced at $1.40 and the LM3671 is priced at $1.60 in 1,000-unit quantities. In the spring of 2005, the LM3671 will be available in National's very small, proprietary micro SMD chip-scale package, measuring just 1.4 mm by 1.1 mm.

LM360 data sheet

LM3671 data sheet

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