ADT7467ARQZ-R7 datasheet(37/77 Pages) ONSEMI

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ADT7467

Rev. 3 | Page 37 of 77 | www.onsemi.com

Dynamic TMIN Control Overview

Dynamic TMIN control mode builds on the basic automatic fan

control loop by adjusting the TMIN value based on system

performance and measured temperature. Therefore, instead of

designing for the worst case, the system thermals can be defined

as operating zones. ADT7467 can self-adjust its fan control loop

to maintain either an operating zone temperature or a system

target temperature. For example, users can specify that the

ambient temperature in a system be maintained at 50°C. If the

temperature is below 50°C, the fans may not run or may run

very slowly. If the temperature is higher than 50°C, the fans may

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 psychoacoustic reasons). Optimizing the

automatic fan control mode involves characterizing the system

to determine the best TMIN and TRANGE settings for the control

loop and the PWMMIN value that produces the quietest fan

speed setting. Using the ADT7467 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 ADT7467 dynamically

alters the control solution to maintain each zone temperature as

closely as possible to its target operating point.

Operating Point Registers

Figure 52 shows an overview of the parameters that affect the

operation of the dynamic TMIN control loop.

TLOW TMIN OPERATING

POINT

THIGH

TRANGE

TEMPERATURE

TTHERM

Figure 52. Dynamic TMIN Control Loop

Table 14 provides a brief description of each parameter.

Table 14. 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 in

automatic fan speed control mode.

Operating

Point

The target temperature for a particular

temperature zone. The ADT7467 attempts to

maintain system temperature at approximately

the operating point by adjusting the TMIN

parameter of the control loop.

THERM

If the temperature exceeds this critical limit, the

fans can run at 100% for maximum cooling.

TRANGE

Programs the PWM duty cycle vs. temperature

control slope.

Dynamic TMIN 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 as described in Step 1 to Step 8 in the

Programming the Automatic Fan Speed Control Loop section,

and then proceed with dynamic TMIN control mode programming.

ADT7467ARQZ-R7 Datasheet(PDF) 37 Page - ON Semiconductor

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