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ADT7462ACPZ-R7 データシート(PDF) 39 Page - ON Semiconductor |
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ADT7462ACPZ-R7 データシート(HTML) 39 Page - ON Semiconductor |
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39 / 81 page  ADT7462 http://onsemi.com 39 Note on 4−Wire Fans The control range for 4−wire fans is much wider than that of 2−wire or 3−wire fans. In many cases, 4−wire fans can start with a PWM drive of as little as 20%. Figure 62. TRANGE and % Fan Speed Slopes for VRM, Ambient, and CPU Temperature Channels TEMPERATURE ABOVE TMIN 0 102030 40 100 50 60 70 80 90 0 10 20 30 40 50 60 70 80 90 100 TEMPERATURE ABOVE TMIN 0 10 20 30 40 50 60 70 80 90 100 0 102030 40 100 50 60 70 80 90 Step 6—TTHERM for Temperature Channels TTHERM is the absolute maximum temperature allowed on a temperature channel. Above this temperature, a component such as the CPU or VRM might be operating beyond its safe operating limit. When the measured temperature exceeds TTHERM, all fans are driven at 100% PWM duty cycle (full speed) to provide critical system cooling. The fans remain running at 100% until the temperature drops below TTHERM minus hysteresis, where hysteresis is the number programmed into Local/Remote 1 Hysteresis Register 0x54 and Remote 2/Remote 3 Hysteresis Register 0x55. The default hysteresis value is 4 °C. The TTHERM limit should be considered as the maximum worst−case operating temperature of the system. Because exceeding any TTHERM limit runs all fans at 100%, it has very negative acoustic effects. Ultimately, this limit should be set up as a fail−safe, and it must not be exceeded under normal system operating conditions. Note that the TTHERM limits cannot be masked, and they affect the fan speed no matter how the automatic fan control settings are configured. This allows some flexibility because a TRANGE value can be selected based on its slope, while a hard limit (such as 70 °C), can be programmed as TMAX (the temperature at which the fan reaches full speed) by setting TTHERM to that limit (for example, 70°C). THERM Registers Register 0x4C, Local THERM1 temperature limit = 0xA4 (100 °C default) Register 0x4D, Remote 1 THERM1 temperature limit = 0xA4 (100 °C default) Register 0x4E, Remote 2 THERM1 temperature limit = 0xA4 (100 °C default) Register 0x4F Remote 3 THERM1 temperature limit = 0xA4 (100 °C default) Register 0x50, Local THERM2 temperature limit = 0xA4 (100 °C default) Register 0x51, Remote 1 THERM2 temperature limit = 0xA4 (100 °C default) Register 0x52, Remote 2 THERM2 temperature limit = 0xA4 (100 °C default) Register 0x53 Remote 3 THERM2 temperature limit = 0xA4 (100 °C default) Hysteresis Registers Register 0x54, Local/Remote 1 Temperature Hysteresis Register Bits [7:4], local temperature hysteresis (4 °C default) Bits [3:0], Remote 1 temperature hysteresis (4 °C default) Register 0x55, Remote 2/Remote 3 Temperature Hysteresis Register Bits [7:4], Remote 2 temperature hysteresis (4 °C default) Bits [3:0], Remote 3 temperature hysteresis (4 °C default) Because each hysteresis setting is four bits, hysteresis values are programmable from 1 °C to 15°C. It is not recommended that hysteresis values ever be programmed to 0 °C, because this value disables hysteresis. In effect, this value causes the fans to cycle between normal speed and 100% speed, creating unsettling acoustic noise. |
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