NATIONAL Semiconductor, represented in Australia by Arrow Electronics , has released the first two products in a family of miniature, high-efficiency synchronous step-down dc-dc converters for portable systems.
The LM3670 and LM3671 optimise 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.
They have automatic pulse frequency modulation - pulse width modulation (PFM-PWM) mode operation which delivers the highest efficiency over the entire load. Their synchronous rectification attribute achieves up to 95% efficiency during continuous switching operation. They have typical quiescent current at 16μA, resulting in excellent stand-by times that extend battery life. They generate less than 5mV peak-to-peak output voltage ripple, making them suitable for RF-based portable systems. The small 2.2μH inductor, 10μF output capacitors and SOT-23 package minimise the footprint size.
The LM3671 powers low-voltage circuits operating from a Lithium-Ion battery or 2.8V-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 2.2μH inductor and two 10μF 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 leads to high-efficiency performance over the complete load range. 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 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 3.3V, 1.875V, 1.8V, 1.6V, 1.5V, 1.375V, 1.25V, 1.2V output voltage options as well as an adjustable option for other voltages.
The LM3670 is the low-power version of the LM3671 and is optimised for systems and applications with lower output current requirements. It switches at 1MHz and has a load capability of up to 300mA. The LM3670 requires a very small 10μH inductor and two 4.7μF capacitors for operation. It is available in 1.8V, 1.875V and 1.5V output voltage options and an adjustable option for other voltages.