New Miniature DC-DC Converters With 95% Efficiency

National Releases 2MHz, 600mA DC-DC Converters in SOT23-5 Package, Maximizing Battery Life in Portable Devices

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 16µA 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 2.2uH inductor, 10uF 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 uH inductor and two 10 uF capacitors. The LM3671’s high-output voltage accuracy, low-output voltage ripple and fast transient response enable peak processor MIPS (million instructions per second).

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 16µA under light loads and during system standby. In shutdown mode (enable pin pulled low), the device turns off and reduces battery consumption to 0.1µA 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 uH inductor and two 4.7uF capacitors for operation.

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.

The Texas Instruments website address is www.ti.com
[Reprinted with kind permission from National Semiconductor]