Low-Noise Bias Supply in µMAX with Power OK for GaAsFET PA

The MAX881R low-noise, inverting power supply is designed for biasing GaAsFET power amplifiers in portable wireless applications. This device is a chargepump inverter followed by a negative linear regulator. The input voltage range is 2.5V to 5.5V. The output is preset at -2.0V or can be set, using two resistors, to any voltage from -0.5V to (-VIN + 0.6V). It can deliver up to 4mA. The internal linear regulator also filters the output to 1mVP-P ripple and noise.

Other features include a power-OK (active-low POK) output that signals when the negative voltage is within 7.5% of its set point. It protects the GaAsFET by not allowing power to be applied to the GaAsFET's drain until it is properly biased. The signal can be routed either to a microcontroller or directly to a switch at the GaAsFET drain. The MAX881R is available in a 10-pin µMAX® package.

Applications

* Cell Phones Wireless Modems * PCS Phones Two-Way Pagers * PHS Phones Mobile Radios * Wireless Handsets Wireless Computers

* Small µMAX Package

* 1mVP-P Output Voltage Ripple and Noise

* Power-OK Signal to Control GaAsFET Drain Switch

* 0.05µA Logic-Controlled Shutdown

* 1ms Guaranteed Startup

* 2.5V to 5.5V Input

* -0.5V to (-VIN + 0.6V) Output at up to 4mA

* Operates with One 4.7µF and Three 0.22µF Capacitors (no inductors needed)