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ADT7462ACPZ-R7 数据表(PDF) 45 Page - ON Semiconductor |
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ADT7462ACPZ-R7 数据表(HTML) 45 Page - ON Semiconductor |
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45 / 81 page  ADT7462 http://onsemi.com 45 Bit 0 (Remote 1 En) = 1 enables dynamic TMIN control on the Remote 1 temperature channel. The chosen TMIN value is dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. Bit 0 (Remote 1 En) = 0 disables dynamic TMIN control. The TMIN value chosen is not adjusted, and the channel behaves as described in the Automatic Fan Control Overview section. Step 10—Monitoring THERM Using the operating point limit ensures that the dynamic TMIN control mode is operating in the best possible acoustic position, while ensuring that the temperature never exceeds the maximum operating temperature. Using the operating point limit allows TMIN to be independent of system−level issues because of its self−corrective nature. In PC design, the operating point for the chassis is usually the worst−case internal chassis temperature. The optimal operating point for the processor is determined by monitoring the thermal monitor in the Intel Pentium 4 processor. To do this, the PROCHOT output of the Pentium 4 is connected to the THERM input of the ADT7462. The operating point for the processor can be determined by allowing the current temperature to be copied to the operating point register when the PROCHOT output pulls the THERM input low on the ADT7462. This gives the maximum temperature at which the Pentium 4 can run before clock modulation occurs. Enabling the THERM Trip Point as the Operating Point Bits [5:2] of Dynamic TMIN Control Register 1 (0x0B) enable/disable THERM monitoring to program the operating point. Table 39 details how the remote temperatures can be copied into the operating point registers on a THERM assertion. Setting these bits to 1 uses the remote temperature as the operating point temperature, overwriting the programmed operating point value in the event of a THERM assertion. Setting these bits to 0 ignores a THERM assertion, and the operating point register remains at the programmed value. Enhancing System Acoustics Automatic fan speed control mode reacts instantaneously to changes in temperature; that is, the PWM duty cycle responds immediately to temperature change. Any impulses in temperature can cause an impulse in fan noise. For psycho−acoustic reasons, the ADT7462 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 cycling up and down, annoying the user. Acoustic Enhancement Mode Overview Figure 74 gives a top−level overview of the automatic fan control circuitry on the ADT7462 and shows where acoustic enhancement fits in. Acoustic enhancement is intended as a post−design tweak made by a system or mechanical engineer evaluating 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 without causing user annoyance due to fan cycling. It is important to realize that although a system might pass an acoustic noise requirement specification (for example, 36 dB), if the fan is annoying, it fails the consumer test. 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 74. Acoustic Enhancement Smoothes Fan Speed Variations Under Automatic Fan Speed Control |
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