General Description
The MAX6650/MAX6651 fan controllers use an SMBus/I2C-compatible interface to regulate and monitor the speed of 5VDC/12VDC brushless fans with built in tachometers. They automatically force the fan’s tachometer frequency (fan speed) to match a preprogrammed value in the Fan-Speed Register by using an external MOSFET or bipolar transistor to linearly regulate the voltage across the fan. The MAX6650 regulates the speed of a single fan by monitoring its tachometer
output. The MAX6651 also regulates the speed of a single fan, but it contains additional tachometer inputs to monitor up to four fans and control them as a single unit when they are used in parallel.

FEATUREs
♦Closed/Open-Loop Fan-Speed Control for 5V/12V Fans
♦2-Wire SMBus/I2C-Compatible Interface
♦Monitors Tachometer Output
   Single Tachometer (MAX6650)
  Up to Four Tachometers (MAX6651)
♦Programmable Alert Output
♦GPIOs
♦Hardware Full-On Override
♦Synchronize Multiple Fans
♦Four Selectable Slave Addresses
♦3V to 5.5V Supply Voltage
♦Small Packages
  10-Pin µMAX (MAX6650)
  16-Pin QSOP (MAX6651)