MAX840, MAX843, MAX844稳压型GaAsFET偏置电源应用电路

概述

The MAX840/MAX843/MAX844 low-noise, inverting charge-pump power supplies are ideal for biasing GaAsFETs in cellular telephone transmitter amplifiers. They operate with inputs down to 2.5V.

The MAX840 offers both a -2V preset output and a -0.5V to -9.4V adjustable output. The MAX843/MAX844 use an external positive control voltage to set the negative output voltage. Input voltage range for all the devices is 2.5V to 10V, and output current is 4mA with VIN > 2.7V. These circuits can operate with small capacitors, as low as 0.22µF.

An internal linear regulator reduces the MAX840's output voltage ripple to 1mVp-p. With a well-filtered control voltage (VCTRL), the MAX843/MAX844 also achieve less than 1mVp-p typical output ripple. Supply current is 750µA, and reduces to less than 1µA in shutdown (MAX840/MAX843). The MAX844's unregulated output is active in shutdown, with the charge pump switching at 20kHz. It provides a low-power LCD supply.

关键特性

Fixed -2V or Adjustable -0.5V to -9.4V Output at 4mA (MAX840)
2.5V to 10V Input Voltage Range
Operate with Small Capacitors (as low as 0.22µF)
1mVp-p Output Voltage Ripple
Charge-Pump Switching Frequency:
100kHz in Normal Operation
20kHz in Shutdown Mode (MAX844)
1µA Max Logic-Level Shutdown Over Temp. (MAX840/MAX843)
Small 8-Pin SO Package

应用/使用
蜂窝电话
连续可调的GaAsFET偏置
GaAsFET功率放大器模块
LCD偏置对比度控制
个人通信装置、PDA
稳定的负电源

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