National Semiconductor introduced a family of miniature, synchronous step-down DC-DC converters for portable systems. 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 quiescent current at 16 microampere typical. 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 microHenry inductor, 10 microFarad output capacitors and SOT-23 package minimize the footprint size. Key Technical Specifications of National’s New LM3671 and LM3670

The LM3671 powers low-voltage circuits operating from a Lithium-Ion battery or 2.8V to 5.5V voltage rails. It has a load capability of up to 600mA. The LM3671’s 2MHz oscillator frequency enables the use of three very small external components for operation, including a 2.2 microHenry inductor and two 10 microFarad 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 features and performance for powering digital cores and peripherals in portable systems. Fixed-frequency PWM mode drives loads from approximately 70mA to 600mA while the PFM mode takes over at lower loads.  PFM mode extends battery life through the reduction of quiescent current to typically 16 microampere 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 microampere 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 300mA. The LM3670 requires a very small 10 microHenry inductor and two 4.7 microFarad 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. 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.