ADT7473 Datasheet, PDF (48/76 Pages) Analog Devices – dBCool Remote Thermal Monitor and Fan Controller

ADT7473
Dynamic T_MIN Control Overview
Dynamic TMIN control mode builds upon the basic automatic
fan control loop by adjusting the TMIN value based on system
performance and measured temperature. This is important
because instead of designing for the worst case, the system
thermals can be defined as operating zones. The ADT7473 can
self-adjust its fan control loop to maintain either an operating
zone temperature or a system target temperature. For example,
it can be specified 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 TMIN and TRANGE settings for the
control loop, and the best PWMMIN value for the quietest fan
speed setting. Using the ADT7473’s dynamic TMIN control
mode, however, shortens the characterization time and
alleviates tweaking the control loop settings because the device
can self-adjust during system operation.
Dynamic TMIN control mode is operated by specifying the
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
Register 0x33, Remote 1 Operating Point = 0xA4
(100°C default)
Register 0x34, Local Temperature Operating Point = 0xA4
(100°C default)
Register 0x35, Remote 2 Operating Point = 0xA4
(100°C default)
Figure 63 shows an overview of the parameters that affect the
operation of the dynamic TMIN control loop.
TEMPERATURE
T_LOW
T_MIN OPERATING T_HIGH T_THERM T_RANGE
POINT
Figure 63. Dynamic TMIN Control Loop
Table 15 provides a brief description of each parameter.
Table 15. TMIN Control Loop Parameters
Parameter Description
TLOW
If the temperature drops below the TLOW limit, an
error flag is set in a status register and an
SMBALERT interrupt can be generated.
THIGH
If the temperature exceeds the THIGH limit, an
error flag is set in a status register and an
SMBALERT interrupt can be generated.
TMIN
The temperature at which the fan turns on
under automatic fan speed control.
Operating
Point
The target temperature for a particular
temperature zone. The ADT7473 attempts to
maintain system temperature at about the
operating point by adjusting the TMIN parameter
of the control loop.
T_THERM
If the temperature exceeds this critical limit, the
fans can be run at 100% for maximum cooling.
TRANGE
Programs the PWM duty cycle vs. temperature
control slope.
Dynamic T_MIN Control Programming
Because the dynamic TMIN control mode is a basic extension of
the automatic fan control mode, program the automatic fan
control mode parameters first, as described in Step 1: Hardware
Configuration to Step 8: THYST for Temperature Channels, then
proceed with dynamic TMIN control mode programming.
Rev. A | Page 48 of 76