Automatic PWM Fan-Speed Controllers with Overtemperature Output
General Description
The MAX6643/MAX6644/MAX6645 monitor temperature and automatically adjust fan speed to ensure optimum cooling while minimizing acoustic noise from the fan.
Each device measures two temperature locations.
The MAX6643/MAX6644/MAX6645 generate a PWM waveform that drives an external power transistor, which in turn modulates the fan’s power supply. The MAX6643/MAX6644/MAX6645 monitor temperature and adjust the duty cycle of the PWM output waveform to control the fan’s speed according to the cooling needs of the system. The MAX6643 monitors its own die temperature and an optional external transistor’s temperature, while the MAX6644 and MAX6645 each monitor the temperatures of one or two external diode-connected transistors.
The MAX6643 and MAX6644 have nine selectable trip temperatures (in 5°C increments). The MAX6645 is factory programmed and is not pin selectable.
All versions include an overtemperature output (OT). OT can be used for warning or system shutdown. The MAX6643 also features a FULLSPD input that forces the PWM duty cycle to 100%. The MAX6643/MAX6644/MAX6645 also feature a FANFAIL output that indicates a failed fan. See the Selector Guide for a complete list of each device’s functions.
The MAX6643 and MAX6644 are available in a small 16-pin QSOP package and the MAX6645 is available in a 10-pin µMAX® package. All versions operate from 3.0V to 5.5V supply voltages and consume 500µA (typ) supply current.

Applications
Networking Equipment
Storage Equipment
Servers
Desktop Computers
Workstations

Features
♦ Simple, Automatic Fan-Speed Control
♦ Internal and External Temperature Sensing
♦ Detect Fan Failure Through Locked-Rotor Output, Tachometer Output, or Fan-Supply Current Sensing
♦ Multiple, 1.6% Output Duty-Cycle Steps for Low Audibility of Fan-Speed Changes
♦ Pin-Selectable or Factory-Selectable Low-Temperature Fan Threshold
♦ Pin-Selectable or Factory-Selectable High-Temperature Fan Threshold
♦ Spin-Up Time Ensures Fan Start
♦ Fan-Start Delay Minimizes Power-Supply Load at Power-Up
♦ 32Hz PWM Output
♦ Controlled Duty-Cycle Rate-of-Change Ensures Good Acoustic Performance
♦ 2°C Temperature-Measurement Accuracy
♦ FULLSPD/FULLSPD Input Sets PWM to 100%
♦ Pin-Selectable OT Output Threshold
♦ 16-Pin QSOP and 10-Pin µMAX Packages