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ADT7476AARQZ-R Datasheet(PDF) 46 Page - ON Semiconductor |
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ADT7476AARQZ-R Datasheet(HTML) 46 Page - ON Semiconductor |
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46 / 69 page ![]() ADT7476A www.onsemi.com 46 Step 8 − THYST for Temperature Channels THYST is the amount of extra cooling a fan provides after the temperature measured has dropped back below TMIN before the fan turns off. The premise for temperature hysteresis (THYST) is that without it, the fan would merely chatter, or cycle on and off regularly, whenever the temperature hovers around the TMIN setting. The THYST value chosen determines the amount of time needed for the system to cool down or heat up as the fan is turning on and off. Values of hysteresis are programmable in the range 1 °C to 15°C. Larger values of THYST prevent the fans from chattering on and off. The THYST default value is set at 4 °C. The THYST setting applies not only to the temperature hysteresis for fan on/off, but the same setting is used for the TTHERM hysteresis value, described in Step 6 - TRANGE for Temperature Channels. Therefore, programming Register 0x6D and Register 0x6E sets the hysteresis for both fan on/off and the THERM function. In some applications, it is required that fans not turn off below TMIN but remain running at PWMMIN. Bits [7:5] of Enhance Acoustics Register 1 (0x62) allow the fans to be turned off or to be kept spinning below TMIN. If the fans are always on, the THYST value has no effect on the fan when the temperature drops below TMIN. THERM Hysteresis Any hysteresis programmed via Register 0x6D and Register 0x6E also applies hysteresis on the appropriate THERM channel. Figure 65. The THYST Value Applies to Fan On/Off Hysteresis and THERM Hysteresis THERMAL CALIBRATION REMOTE1 = AMBIENT TEMP 100% 0% TMIN TRANGE PWM MIN MUX S TACHOMETER1 MEASUREMENT S S PWM MIN PWM MIN THERMAL CALIBRATION 100% 0% TMIN TRANGE THERMAL CALIBRATION 100% 0% TMIN TRANGE LOCAL = VRM TEMP REMOTE2 = CPU TEMP TACHOMETER2 MEASUREMENT RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER3 AND 4 MEASUREMENT PWM CONFIG PWM GENERATOR PWM1 PWM2 PWM3 TACH3 TACH2 TACH1 CPU FAN SINK FRONT CHASSIS REAR CHASSIS RAMP CONTROL (ACOUSTIC ENHANCEMENT) RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM CONFIG PWM GENERATOR PWM CONFIG PWM GENERATOR TMIN 100% 0% TTHERM TRANGE |
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