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ADT7467ARQZ-R7 Datasheet(PDF) 35 Page - ON Semiconductor |
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ADT7467ARQZ-R7 Datasheet(HTML) 35 Page - ON Semiconductor |
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35 / 77 page  ADT7467 Rev. 3 | Page 35 of 77 | www.onsemi.com AUTOMATIC FAN CONTROL OVERVIEW The ADT7467 can automatically control the speed of fans based on the measured temperature. This is done independently of CPU intervention once initial parameters are set up. The ADT7467 has a local temperature sensor and two remote temperature channels that can be connected to a CPU on-chip thermal diode (available on Intel Pentium class and other CPUs). These three temperature channels can be used as the basis for automatic fan speed control to drive fans using pulse- width modulation (PWM). Automatic fan speed control reduces acoustic noise by optimizing fan speed according to accurately measured temperature. Reducing fan speed can also decrease system current consump- tion. The automatic fan speed control mode is very flexible due to the number of programmable parameters, including TMIN and TRANGE. The TMIN and TRANGE values for a temperature channel and, therefore, for a given fan are critical because they define the thermal characteristics of the system. Thermal validation of the system is one of the most important steps in the design process; therefore, these values should be selected carefully. Figure 49 shows a top-level overview of the automatic fan control circuitry on the ADT7467. From a systems-level perspective, up to three system temperatures can be monitored and used to control three PWM outputs. The three PWM outputs can be used to control up to four fans. The ADT7467 allows the speed of four fans to be monitored. Each temperature channel has a thermal calibration block, allowing the designer to individually configure the thermal characteristics of each temperature channel. For example, one can decide to run the CPU fan when CPU temperature increases above 60°C and to run a chassis fan when the local temperature increases above 45°C. At this stage, the designer has not assigned these thermal calibration settings to a particular fan drive (PWM) channel. The right side of Figure 49 shows controls that are fan-specific. The designer can individually control parameters such as minimum PWM duty cycle, fan speed failure thresholds, and even ramp control of the PWM outputs. Therefore, automatic fan control ultimately allows gracefully changing fan speed so that it is less perceptible to the system user. MUX THERMAL CALIBRATION 0% TMIN TRANGE THERMAL CALIBRATION 100% 0% TMIN TRANGE THERMAL CALIBRATION 100% 0% TMIN TRANGE REMOTE 1 TEMP LOCAL TEMP REMOTE 2 TEMP TACHOMETER 1 MEASUREMENT PWM CONFIG PWM MIN PWM1 RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM GENERATOR TACHOMETER 2 MEASUREMENT PWM CONFIG PWM MIN PWM2 RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM GENERATOR TACHOMETER 3 AND 4 MEASUREMENT PWM CONFIG PWM MIN PWM3 RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM GENERATOR 100% TACH1 TACH2 TACH3 Figure 49. Automatic Fan Control Block Diagram |
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