Power Electronics

Converter Enables RF PA Voltage Scaling

Advanced Analogic Technologies’ AAT1171 is a fully integrated voltage-scaling dc-dc step-down converter specifically optimized to control the power to the Power Amplifiers (PAs) in WCDMA and CDMA handsets. By dynamically controlling the operating voltage of the PA, the AAT1171 increases amplifier efficiency and extends talk time.

The device operates across a wide input voltage range of 2.7 V to 5.5 V. Its input voltage is controlled by a real-time output signal from the baseband processor and delivers up to 600 mA of continuous load current.

By supplying a variable output voltage of 0.6 V to 3.6 V, the AAT1171 optimizes PA efficiency at both low and high transmit levels. To meet stringent WCDMA requirements, the output voltage responds in less than 30 µs. To improve efficiency even further, the AAT1171 provides the low quiescent current at both full and light load conditions. No-load quiescent current is only 45 µA (typical).

The AAT1171 also maximizes efficiency and extends handset talk time by providing an integrated 85-mΩ 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 1.3 V.

Operating at 2 MHz switching frequency, the AAT1171 allows the system designer to use a 2.2 µH inductor and 4.7 µF capacitor on the output. The AAT1171 also features current-limiting, short-circuit and over-temperature shutdown protection circuitry to ensure device integrity.

Available now, the AAT1171 is housed in a 12-pin TDFN33 package. The device sells for $1.31 each in 1000-piece quantities.

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