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Buck regulator integrates two LDOs

Posted: 16 Jul 2009 ?? ?Print Version ?Bookmark and Share

Keywords:buck regulator? LDO? DC/DC?

AS1339 buck regulator

austriamicrosystems has unveiled a new low-noise 650mA DC/DC buck regulator that integrates two LDOs and is designed for RF power amplifiers (PAs). The AS1339 step down regulator offers high efficiency and small size. The device suits multiband W-CDMA/NCDMA applications, such as cellular handsets, wireless PDAs and smart phones.

An input voltage range of 2.7V to 5.5V makes the AS1339 suitable for single Li-ion cells. From this input the device delivers up to 650mA. For even longer battery lifetime low power RF amplifiers can scale the output power dynamically by changing its supply voltage. This is doable because the output voltage of the AS1339 is dynamically controlled by an external analogue input signal. Also, the 30?s settling time of the output voltage ensures CDMA-specifications are not exceeded.

As small as the AS1339 already is in its 2mm x 2mm WL-CSP package, it shrinks PCB footprint even more because its 2MHz fixed switching frequency allows the use of tiny low profile inductors and capacitors. This constant frequency switching results in low predictable output noise which is additionally reduced by the internal noise reduction circuitry.

Bruce Ulrich, marketing director for standard linear at austriamicrosystems describes the AS1339 as "the perfect symbiosis between efficiency and analog performance."

Power efficiency
With 97 percent peak efficiency the AS1339 boosts battery lifetime in any application. Supporting 1.1A of peak current, the integrated 110m? bypass FET provides maximum power with minimum dropout under even low-battery conditions. The AS1339 enters bypass mode automatically during high power transmissions. The AS1339 also integrates two 10mA low-noise, high-PSRR LDO, making them suitable for PA biasing. Each LDO features a separate enable, provides high output voltage accuracy, and requires only 10nF of output capacitance.

Moreover if the supply is not required, for example mobile phone in-flight mode, the AS1339 offers a 100nA shutdown mode combined with an output disconnect feature. Additional features are soft start and safety features such as current overload and thermal shutdown protection.

The AS1339 is available in 2mm x 2mm WL-CSP 16-bumps covering the industrial temperature range of -40C to +85C.

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