ADT7467_12 Datasheet, PDF (41/72 Pages) ON Semiconductor – Remote Thermal Monitor and Fan Controller

ADT7467
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0
2C
2.5C
3.33C
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13.3C
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26.6C
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53.3C
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TEMPERATURE ABOVE T_MIN
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TEMPERATURE ABOVE T_MIN
2C
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6.67C
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13.3C
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26.6C
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40C
53.3C
120 ^80C
Figure 64. T_RANGE and Percentage of Fan Speed
Slopes with PWM_MIN = 20%
Determining T_RANGE for Each Temperature Channel
The following example shows how different T_MIN and
T_RANGE settings can be applied to three thermal zones. In
this example, the following T_RANGE values apply:
T_RANGE = 80C for ambient temperature
T_RANGE = 53.3C for CPU temperature
T_RANGE = 40C for VRM temperature
This example uses the mux configuration described in the
Step 2: Configuring the Mux section, with the ADT7467
connected as shown in Figure 55. Both CPU temperature
and VRM temperature drive the CPU fan connected to
PWM1. Ambient temperature drives the front chassis fan
and the rear chassis fan connected to PWM2 and PWM3.
The front chassis fan is configured to run at
PWM_MIN = 20%; the rear chassis fan is configured to run at
PWM_MIN = 30%. The CPU fan is configured to run at
PWM_MIN = 10%.
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%.
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TEMPERATURE ABOVE T_MIN
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TEMPERATURE ABOVE T_MIN
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Figure 65. T_RANGE and Percentage of Fan Speed
Slopes for VRM, Ambient, and CPU Temperature
Channels
STEP 7: T_THERM for Temperature Channels
T_THERM 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 temperature
measured exceeds T_THERM, 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 T_THERM minus hysteresis, where hysteresis is
the number programmed into the Hysteresis Registers 0x6D
and 0x6E. The default hysteresis value is 4C.
The T_THERM limit should be considered the maximum
worst-case operating temperature of the system. Because
exceeding any T_THERM limit runs all fans at 100%, it has
significant negative acoustic effects. Ultimately, this limit
should be set up as a fail-safe, and users should ensure that
it is not exceeded under normal system operating conditions.
Note that the T_THERM limits are nonmaskable and affect
the fan speed regardless of the configuration of the
automatic fan control settings. This allows some flexibility,
because a T_RANGE value can be selected based on its slope,
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