Analog Devices ADT7473 Manual page 46

ADT7473
Dynamic T Control Overview
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Dynamic T control mode builds upon the basic automatic
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fan control loop by adjusting the T
performance and measured temperature. This is important
because instead of designing for the worst case, the system
thermals can be defined as operating zones. ADT7473 can self-
adjust its fan control loop to maintain either an operating zone
temperature or a system target temperature. For example, one
can specify that the ambient temperature in a system should be
maintained at 50°C. If the temperature is below 50°C, the fans
might not need to run, or might run very slowly. If the
temperature is higher than 50°C, the fans need to throttle up.
The challenge presented by any thermal design is finding the
right settings to suit the system's fan control solution. This can
involve designing for the worst case, followed by weeks of
system thermal characterization, and finally fan acoustic
optimization (for psycho-acoustic reasons). Getting the most
benefit from the automatic fan control mode involves character-
izing the system to find the best T
control loop, and the best PWM
speed setting. Using the ADT7473's dynamic T
mode, however, shortens the characterization time and
alleviates tweaking the control loop settings because the device
can self-adjust during system operation.
Dynamic T control mode is operated by specifying the
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operating zone temperatures required for the system.
Associated with this control mode are three operating point
registers, one for each temperature channel. This allows the
system thermal solution to be broken down into distinct
thermal zones. For example, CPU operating temperature is
70°C, VRM operating temperature is 80°C, and ambient
operating temperature is 50°C. The ADT7473 dynamically
alters the control solution to maintain each zone temperature as
closely as possible to its target operating point.
Operating Point Registers
Reg. 0x33, Remote 1 Operating Point = 0xA4 (100°C default)
Reg. 0x34, Local Operating Point = 0xA4 (100°C default)
Reg. 0x35, Remote 2 Operating Point = 0xA4 (100°C default)
value based on system
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and T settings for the
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value for the quietest fan
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control
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Figure 63 shows an overview of the parameters that affect the
operation of the dynamic T
T T
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Table 13 provides a brief description of each parameter.
Table 13. T
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Parameter
T
LOW
T
HIGH
T
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Operating
Point
T
THERM
T
RANGE
Dynamic T
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Because the dynamic T
the automatic fan control mode, program the automatic fan
control mode parameters first, as described in Step 1 to Step 8,
then proceed with dynamic T
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control loop.
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OPERATING T T T
HIGH THERM RANGE
POINT
Figure 63. Dynamic T Control Loop
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Control Loop Parameters
Description
If the temperature drops below the T
error flag is set in a status register and an
SMBALERT interrupt can be generated.
If the temperature exceeds the T
error flag is set in a status register and an
SMBALERT interrupt can be generated.
The temperature at which the fan turns on
under automatic fan speed control.
The target temperature for a particular
temperature zone. The ADT7473 attempts to
maintain system temperature at about the
operating point by adjusting the T
of the control loop.
If the temperature exceeds this critical limit, the
fans can be run at 100% for maximum cooling.
Programs the PWM duty cycle vs. temperature
control slope.
Control Programming
control mode is a basic extension of
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control mode programming.
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TEMPERATURE
limit, an
LOW
limit, an
HIGH
parameter
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