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DC/DC converter targets WCDMA, CDMA handsets

Posted: 14 Jul 2006 ?? ?Print Version ?Bookmark and Share

Keywords:AnalogicTech? AAT1171? DC/DC step-down converter?

Advanced Analogic Technologies Inc. has released a new fully-integrated voltage-scaling DC/DC step-down converter specifically designed to control power to the power amplifier (PA) in WCDMA and CDMA handsets. By dynamically controlling the operating voltage of the PA in mobile phones, the AAT1171 promises increased amplifier efficiency and extended talk time.

"The stereotypical WCDMA handset transmit profile makes the PA operate at approximately 16dBm output power for about 50 percent to 60 percent of its operating life," said Bill Weiss, product line director for AnalogicTech. "When powered from the AAT1171, instead of being powered directly from the battery, the PA consumes 60 percent less power at this 16dBm level. This tremendous energy savings enables longer battery life, longer talk time, smaller batteries, and thus smaller and lighter weight mobile phones."

The new device operates across a 2.7-5.5V input range. Its input voltage is controlled by a real-time output signal from the baseband processor and delivers up to 600mA of continuous load current. By supplying a variable output voltage of 0.6-3.6V, the device optimizes PA efficiency at both low and high transmit levels, said AnalogicTech. To meet stringent WCDMA requirements, the output voltage responds in less than 30s. The company said the device also provides the lowest quiescent current available on the market today under both full and light load conditions. No load quiescent current is only 45A (typical).

According to AnalogicTech, the new device maximizes efficiency and extends handset talk time by providing an integrated 85-milliohm bypass MOSFET. When transmitting at full power, the MOSFET switch bypasses the DC/DC converter and output inductor to provide a low resistance path between the battery and the PA, allowing the system to operate very close to the minimum battery voltage. The switch is activated by setting the bypass input high or forcing the baseband DAC voltage output to 1.3V.

Operating at 2MHz switching frequency, the device allows the system designer to use a 2.2H inductor and 4.7F capacitor on the output. It also features current-limiting, short-circuit and over-temperature shutdown protection circuitry to ensure device integrity, the company said.

Specified over the -40C to 85C temperature range, the AAT1171 is immediately available in a Pb-free, 12-pin TDFN33 package. The device sells for $1.31 each in 1,000-piece quantities.

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