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ADT7467ARQZ-R7 Datasheet(PDF) 57 Page - ON Semiconductor |
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ADT7467ARQZ-R7 Datasheet(HTML) 57 Page - ON Semiconductor |
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57 / 77 page  ADT7467 Rev. 3 | Page 57 of 77 | www.onsemi.com ENHANCING SYSTEM ACOUSTICS Automatic fan speed control mode reacts instantaneously to changes in temperature, that is, the PWM duty cycle immediately responds to temperature change. Any impulses in temperature can cause an impulse in fan noise. For psychoacoustic reasons, the ADT7467 can prevent the PWM output from reacting instantaneously to temperature changes. Enhanced acoustic mode controls the maximum change in PWM duty cycle at a given time. The objective is to prevent the fan from repeatedly cycling up and down, annoying the user. ACOUSTIC ENHANCEMENT MODE OVERVIEW Figure 81 shows a top-level overview of the ADT7467 automatic fan control circuitry and where acoustic enhancement fits in. Acoustic enhancement is intended as a postdesign tweak made by a system or mechanical engineer evaluating the best settings for the system. Having determined the optimal settings for the thermal solution, the engineer can adjust the system acoustics. The goal is to implement a system that is acoustically pleasing and does not cause user annoyance due to fan cycling. It is important to realize that although a system may pass an acoustic noise requirement specification (for example, 36 dB), it fails the consumer test if the fan is annoying. ACOUSTIC ENHANCEMENT REAR CHASSIS FRONT CHASSIS CPU FAN SINK LOCAL = VRM TEMP PWM1 PWM2 TACH1 TACH2 TACH3 PWM3 REMOTE 1 = AMBIENT TEMP REMOTE 2 = CPU TEMP MUX THERMAL CALIBRATION 0% TMIN TRANGE THERMAL CALIBRATION 100% 0% TMIN TRANGE THERMAL CALIBRATION 100% 0% TMIN TRANGE TACHOMETER 1 MEASUREMENT PWM CONFIG PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM GENERATOR TACHOMETER 2 MEASUREMENT PWM CONFIG PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM GENERATOR TACHOMETER 3 AND 4 MEASUREMENT PWM CONFIG PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM GENERATOR 100% Figure 81. Acoustic Enhancement Smoothes Fan Speed Variations in Automatic Fan Speed Control |
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