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National Semi dc-dc converter suits RF power amps

Posted: 04 Mar 2005 ?? ?Print Version ?Bookmark and Share

Keywords:lm2706? dc-dc converter? national semiconductor?

The LM2706 dc-dc converter from National Semiconductor Corp. is designed for powering RF power amplifiers (PAs) from a single Li-ion cell. It steps down an input voltage from 2.7V to 5.5V to a variable output from 1.5V to 3.25V up to 300mA. The output voltage is set using a VCON analog input for controlling power levels and efficiency of the RF PA, and an internal bypass switch allows direct connection to the battery for maximum power to the RF PA.

The device offers four modes for mobile phones and similar RF power amplifier applications. The fixed-frequency PWM mode minimizes RF interference; the forced bypass mode turns on an internal bypass switch to power the PA directly from the battery; the automatic bypass mode minimizes dropout by turning on the bypass switch when the battery decays to near the output voltage; and the shutdown mode turns the device off and reduces battery consumption to 0.1&microA (typ.).

Additionally, the dc-dc converter offers internal synchronous rectification for high efficiency (95 percent typical at 3.25VOUT, 200mA, 3.9VIN), with the current limit and thermal overload protection features protecting the device and system during fault conditions. With an output voltage ripple of <10mV (typ), this new product features an internal soft start and a high switching frequency (600kHz) that allows use of tiny surface-mount components. In addition, only three small external surface-mount components, an inductor and two ceramic capacitors, are required.

Available in a 10-pin Pb-free micro SMD package, the LM2706 costs $1.50 in 1,000-unit quantities.

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