General Description
The MAX687/MAX688/MAX689 low-dropout linear regulators operate with an input-to-output voltage differential limited only by an external PNP transistor. Outputs are fixed at 3.3V (MAX687/MAX688) or 3.0V (MAX689). The only external components required are a PNP pass transistor and output, compensation, and bypass capacitors. Base drive to the external transistor is at least 10mA, permitting output currents to exceed 1A when using high-gain transistors (β > 100). Output current limiting is implemented by limiting the external transistor’s base current. Output voltage monitoring and shutdown functions are included.

Features
♦ Fixed Outputs:
   3.3V (MAX687/MAX688)
   3.0V (MAX689)
♦ Directly Drives External PNP Transistor
♦ 10mA Min Base-Current Drive for >1A Output
♦ Low Dropout Voltage:
   100mV Dropout at 650mA Output (FZT749)
   40mV Dropout at 200mA Output (FZT749)
   0.8V Dropout at 4A Output
♦ Power-Fail Output Monitors the Output Voltage
♦ Automatic, Latched Shutdown when Output Falls Out
   of Regulation (MAX687)
♦ Precision Threshold Shutdown Control
   (MAX688/MAX689)
♦ Low Supply Current:
   150µA Operating
   <1µA Shutdown
♦ 2.7V to 11.0V Supply Range
♦ 8-Pin DIP/SO/µMAX Packages
♦ <2mV Line Transient with 3.4V to 3.6V Input
♦ Output Accuracy <±2%

Applications
   High-Efficiency Linear Regulator
   Battery-Powered Devices
   Portable Instruments
   Portable Telephones
   Power Supply or Backup Supply for Memory