MAX844

19-0388; Rev 1; 3/96 UAL IT MAN TION K A ET U E L H A S EV TA WS DA FOLLO Low-Noise, Regulated, -2V GaAsFET Bias _______________General Description 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 V IN > 2.7V. These circuits can operate with small capacitors, as low as 0.22µF. An internal linear regulator reduces the MAX840’s out put 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 1 µA 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. ____________________________Features o Fixed -2V or Adjustable -0.5V to -9.4V Output at 4mA (MAX840) o 2.5V to 10V Input Voltage Range o Operate with Small Capacitors (as low as 0.22µF) o 1mVp-p Output Voltage Ripple o Charge-Pump Switching Frequency: 100kHz in Normal Operation 20kHz in Shutdown Mode (MAX844) o 1µA Max Logic-Level Shutdown Over Temp. (MAX840/MAX843) o Small 8-Pin SO Package MA...