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National dc/dc converters deliver 95 percent efficiency

Posted: 16 Sep 2002 ?? ?Print Version ?Bookmark and Share

Keywords:national semiconductor? lm2608? lm2614? lm2618? power management ic?

National Semiconductor Corp, has announced the availability of a series of CMOS power management ICs for low-voltage applications in handsets and other portable devices.

The LM2608, LM2614, and LM2618 magnetic buck dc/dc converters, and LM2788 and LM2798 switched capacitor buck converters are the company's answer for the handheld industry's need to supply low-ripple, precise voltages to processors and power amplifiers while extending battery life.

The magnetic buck dc/dc converters offer precise solutions for powering RF and digital baseband applications with up to 95 percent efficiency at 12 percent accuracy. The devices also deliver 400mA making them suitable for most cellphones and general-purpose processor applications.

Pin selectable output voltages at 1.8, 1.5, 1.3, or 1.05V eliminate the need for an external voltage divider, and 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 optimized for powering low-voltage digital portions of phone handsets. The LM2608 functions in PWM under high current load conditions, but converts to linear mode for light loads with a quiescent current of 205A.

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

The LM2614 increases the efficiency of the RF power amplifier (PA) and allows adaptive voltage scaling for the PA via a simple user application circuit that provides the desired control and transfer functions to position output for maximum efficiency.

The LM2788 and LM2798 step-down converters deliver 120mA regulated low-voltage current from input voltages of 2.8V to 5.5V. They feature fractional gain and gain hopping circuitry to provide efficient operation over a wide range of I/O voltage ratios.

The company claims that all three of the available output voltage options (1.5V, 1.8V, and 2V) can be produced at peak efficiencies in the 80 percent to 90 percent range from a 3.3V rail. Average efficiencies over 80 percent can be achieved supplying nominal loads from a Li-ion battery.

The LM2788/98 switched capacitor converters draw 325A when unloaded, allowing for longer battery life in sleep mode. In addition, the LM2798 has logic output flags that indicate when input and output voltages are at acceptable levels.

Available in the company's die sized microSMD 10-bump package, the LM2608, LM2614, and LM2618 are priced at $1.20 each in quantities of 1,000 units. The LM2788 and LM2798 are available in 8-pin and 10-pin MSOP configurations, and are priced at 89 cents and 99 cents, respectively.

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