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MAX6643, MAX6644, MAX6645

Automatic PWM Fan-Speed Controllers with Overtemperature Output

Automatic PWM Fan-Speed Controllers with Overtemperature Output Eliminate Software Overhead
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Status Explanations for product status codes

Part Number Status
MAX6643 Active: In Production.
MAX6644 Active: In Production.
MAX6645 Active: In Production. But some versions of the family are subject to Last Time Buy. See Ordering Information.


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 (active-low OT). Active-low 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 active-low FANFAIL output that indicates a failed fan. See the Selector Guide in the full data sheet 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.

Data Sheet

Download this datasheet in PDF formatDownload Rev 2 (PDF, 216kB)
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An evaluation board is available: MAX6643LBEVKIT

Key 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
  • Active-Low FULLSPD/FULLSPD Input Sets PWM to 100%
  • Pin-Selectable Active-Low OT Output Threshold
  • 16-Pin QSOP and 10-Pin µMAX Packages


  • Desktop Computers
  • Networking Equipment
  • Servers
  • Storage Equipment
  • Workstations

Key Specifications:

Fan Controllers
Part Number Sensor Type Fan Controller Functions Fan Cntrl. Accuracy
Temp. Thresh.
See Notes
MAX6643  Remote - PWM 2 Programmable $0.93 @1k
MAX6644  Remote & Local Sensor $0.93 @1k
MAX6645  Remote & Local Sensor -
See All Fan Controllers (22)

Pricing Notes:

This pricing is BUDGETARY, for comparing similar parts. Prices are in U.S. dollars and subject to change. Quantity pricing may vary substantially and international prices may differ due to local duties, taxes, fees, and exchange rates. For volume-specific and version-specific prices and delivery, please see the price and availability page or contact an authorized distributor.


MAX6643, MAX6644, MAX6645: Block Diagram
Block Diagram

More Information

New Product Press Release   2004-05-04 ]

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Information Index

Document Ref.: 19-3305 Rev 2; 2007-03-26
This page last modified: 2009-10-12