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ADT7475 Datasheet(PDF) 39 Page - Analog Devices |
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ADT7475 Datasheet(HTML) 39 Page - Analog Devices |
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39 / 68 page  ADT7475 Rev. A | Page 39 of 68 STEP 3: TMIN SETTINGS FOR THERMAL CALIBRATION CHANNELS TMIN is the temperature at which the fans start to turn on under automatic fan control. The speed at which the fan runs at TMIN is programmed later in the process. The TMIN values chosen are temperature channel specific, for example, 25°C for ambient channel, 30°C for VRM temperature, and 40°C for processor temperature. TMIN is an 8-bit value, either twos complement or Offset 64, that can be programmed in 1°C increments. There is a TMIN register associated with each temperature measure- ment channel: Remote 1, local, and Remote 2 temperatures. Once the TMIN value is exceeded, the fan turns on and runs at the minimum PWM duty cycle. The fan turns off once the temperature has dropped below TMIN − THYST. To overcome fan inertia, the fan is spun up until two valid TACH rising edges are counted. See the Fan Startup Timeout section for more details. In some cases, primarily for psycho- acoustic reasons, it is desirable that the fan never switch off below TMIN. Bits [7:5] of Enhance Acoustics Register 1 (0x62), when set, keep the fans running at the PWM minimum duty cycle, if the temperature should fall below TMIN. TMIN Registers Register 0x67, Remote 1 Temperature TMIN = 0x9A (90°C) Register 0x68, Local Temperature TMIN = 0x9A (90°C) Register 0x69, Remote 2 Temperature TMIN = 0x9A (90°C) Enhance Acoustics Register 1 (0x62) Bit 7 (MIN3) = 0, PWM3 is off (0% PWM duty cycle) when temperature is below TMIN − THYST. Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty cycle below TMIN − THYST. Bit 6 (MIN2) = 0, PWM2 is off (0% PWM duty cycle) when temperature is below TMIN − THYST. Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty cycle below TMIN − THYST. Bit 5 (MIN1) = 0, PWM1 is off (0% PWM duty cycle) when temperature is below TMIN − THYST. Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty cycle below TMIN − THYST. 0% 100% TMIN 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 PWM MIN PWM MIN PWM MIN 100% PWM GENERATOR PWM GENERATOR TACHOMETER 3 AND 4 MEASUREMENT TACHOMETER 1 MEASUREMENT TACHOMETER 2 MEASUREMENT RAMP CONTROL (ACOUSTIC ENHANCEMENT) RAMP CONTROL (ACOUSTIC ENHANCEMENT) RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM GENERATOR PWM CONFIG PWM CONFIG PWM CONFIG Figure 49. Understanding the TMIN Parameter |
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