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  • Tiny Predictive Fan Failure Detector
    The TC670 is an integrated fan speed sensor that detects and/or predicts fan failure, preventing thermal damage to systems with cooling fans. When the fan speed falls below a user-specified level, the TC670 asserts an ALERT signal. With this design, a critical minimum fan speed is determined by the user.
    http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en010730
  • Interfacing Microchip’s Fan Speed Controllers to a SPI™
    Microchip's TC642, TC643, and TC646 are the world's first integrated circuits dedicated for controlling and monitoring fan speed. The new family of fan speed controllers modulate fan speed to compensate for changes in system temperature.
    http://ww1.microchip.com/downloads/en/AppNotes/00767a.pdf
  • Speed Error in PWM Fan Control Systems
    Brushless DC fan speed can be varied using pulse-width modulation. The typical pulse-width modulation control scheme inserts a power switch in series with the fan. In such applications, an increase in the active duty cycle causes a corresponding increase in fan speed (i.e., fan speed is proportional to tON/(tON + tOFF). Conventional wisdom states that pulse-width modulation duty cycle alone determines operating speed (for example, the fan speed runs at 50% of maximum when the pulse-width modulation duty cycle is 50%). In reality, the fan operates at a higher percentage of full speed for any given duty cycle. The resulting difference between actual fan speed and the corresponding pulse-width modulation duty cycle (herein referred to as Speed Error) can be problematic in open loop fan control systems.
    http://ww1.microchip.com/downloads/en/AppNotes/00772b.pdf
  • Four-Speed Fan Control Using Simple Remote Diode Temperature Sensor
    The circuit shown in this document controls the speed of a 12V DC fan using an LM88 Remote Diode Temperature Sensor (RDTS) IC. The LM88 is a dual remote diode temperature sensor with three digital comparators and has three open-drain outputs that can be used as interrupts or to signal system shutdown. The digital comparators can be programmed independently to make a greater than or less than comparison.
    http://www.national.com/an/AN/AN-1262.pdf
  • Programming the Automatic Fan Speed Control Loop
    The ADT7460/ADT7463 have a local temperature sensor and two remote temperature channels that may be connected to an on-chip diode-connected transistor on a CPU. These three temperature channels may be used as the basis for automatic fan speed control to drive fans using pulsewidth modulation (PWM).
    http://www.analog.com/UploadedFiles/Application_Notes/3601910093957551549331085006AN613_0.pdf

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