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Power management for portable devices

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article image Converters offering precise solutions.

NATIONAL Semiconductor, distributed in Australia by Arrow Electronics , has announced a series of CMOS power management ICs for low-voltage applications in handsets and portable devices.

The new dc/dc buck converters provide an efficient solution to the handheld industry's continual challenge to supply low-ripple, precise voltages to processors and power amplifiers while extending battery life in portable devices.

The LM2608, LM2614 and LM2618 are magnetic buck dc/dc converters that offer precise solutions for powering RF and digital baseband applications with up to 95% efficiency at ±2% accuracy.

The magnetic converters are the best choice when efficiency is important. The converters put out up to 400mA, which optimises them for most cell phone and general-purpose processor applications.

Pin selectable output voltages at 1.8V, 1.5V, 1.3V or 1.05V eliminate the need for an external voltage divider. They also allow the system designer to dynamically scale back the operating voltage to reduce the power for low frequency operating modes.

The LM2608 and LM2618 are dual-mode converters optimised for powering low-voltage digital portions of phone handsets. The LM2608 functions in PWM (pulse width modulation) under high current load conditions, but converts to linear mode for light loads with a low operating quiescent current (Iq) of 20 microAmps.

Like the LM2608, the LM2618 operates in PWM under high current load conditions. Its second mode is pulse frequency modulation (PFM), efficient for 1 to 50mA loads encountered in low-level, background processing tasks.

The LM2614 is a flexible part that increases the efficiency of the RF power amplifier (PA), which is one of the largest consumers of power in a cellular handset, and also allows adaptive voltage scaling for the PA.

The LM2788 and LM2798, which require no external inductors, are among the industry's smallest step-down converters. They produce a 120mA regulated low-voltage current from input voltages of 2.8V to 5.5V.

State-of-the-art fractional gain and gain hopping circuitry provides efficient operation over a wide range of input to output voltage ratios.

All three of the available output voltage options (1.5V, 1.8V and 2.0V) can be produced at peak efficiencies in the 80% to 90% range from a 3.3-volt rail.

Average efficiencies over 80% can be achieved supplying nominal loads from a Lithium-ion battery over the full range of LiIon voltages.

The LM2788/98 switched capacitor converters have a low operating supply current of only 32 microAmps when unloaded, allowing for long battery life in sleep mode.

The LM2798 has logic output flags that indicate when input and output voltages are at acceptable levels. The LM2788/98 can be used to power low-voltage microprocessors and other low-voltage circuits in a wide variety of applications, including digital cameras, cell phones, PCs and PC peripherals such as rechargeable Bluetooth devices or USB flash storage systems.

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