19-1448; Rev 3; 8/02
Low-Cost, Low-Voltage, PA Power Control Amplifier for GSM Applications in 8-Pin QFN
General Description
The MAX4473 PA power control IC is intended for closed-loop bias control of GSM power amplifiers. The device facilitates accurate control of the current delivered to the power amplifier (PA) through a control voltage. The error amplifier senses the voltage drop across an external current-sense resistor placed between the supply and the PA. The output of the error amplifier adjusts the PA gain until the current is proportional to the power control voltage applied to the MAX4473. This unique topology is useful in time-division-multipleaccess (TDMA) systems, such as GSM, where accurate transmit burst shaping and power control is required. User-selectable current sensing and gain setting resistors maximize flexibility. The MAX4473 operates from a single 2.7V to 6.5V supply and typically draws 1.2mA of supply current. The error amplifier has a common-mode range that extends from 1V to V CC . The power control input and error amplifier outputs swing Rail-to-Rail. A low-power shutdown mode reduces supply current to less than 1A and activates an on-board active pull-down at the error amplifier output. Fast enable/disable times of 0.9s reduce average power consumption without compromising dynamic performance. The MAX4473 is available in a space-saving 8-pin QFN package.
Features
o Optimized for GSM Timing Requirements o 2.7V to 6.5V Single-Supply Operation o 1.2mA Supply Current o ≤1A Supply Current in Shutdown Mode o Guaranteed 1.5s Enable/Disable Times o Active Output Pull-Down in Shutdown Mode o Rail-to-Rail Error Amplifier Output o Rail-to-Rail Power Control Input o Output Drive Capability—500 and 300pF Loads o 1V to VCC Current Sense Input Common-Mode Voltage Range o No Phase-Reversal for Common-Mode Voltage from 0 to VCC o External Current Sensing and Gain Setting Resistors Maximize Flexibility o Available in a Space-Saving 8-Pin QFN

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