ADT7462ACPZ-R7 datasheet(41/81 Pages) ONSEMI

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ADT7462

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Figure 65. Chassis Airflow Issues

FAN

I/O CARDS

POOR CPU

AIRFLOW

VENTS

POWER

SUPPLY

CPU

DRIVE

BAYS

GOOD VENTING =

GOOD AIR EXCHANGE

POOR VENTING =

POOR AIR EXCHANGE

VENTS

FAN

I/O CARDS

GOOD CPU AIRFLOW

FAN

VENTS

POWER

SUPPLY

CPU

DRIVE

BAYS

• Worst−Case Processor Power Consumption

This data sheet maximum does not necessarily reflect

the true processor power consumption. Designing for

worst−case CPU power consumption can result in a

processor becoming over−cooled (generating excess

system noise).

• Worst−Case Peripheral Power Consumption

The tendency is to design to data sheet maximums for

peripheral components (again over−cooling the

system).

• Worst−Case Assembly

Every system manufactured is unique because of

manufacturing variations. Heat sinks may be loose

fitting or slightly misaligned. Too much or too little

thermal grease may be used. Variations in application

pressure for thermal interface material can affect the

efficiency of the thermal solution. Accounting for

manufacturing variations in every system is difficult;

therefore, the system must be designed for the

worst−case.

Figure 66. Thermal Model

SUBSTRATE

HEAT

SINK

THERMAL

INTERFACE

MATERIAL

INTEGRATED

HEAT

SPREADER

EPOXY

THERMAL INTERFACE MATERIAL

PROCESSOR

θCA

θSA

θTIMS

θCTIM

θTIMC

θJTIM

θCS

TTIM

θJA

Although a design usually accounts for worst−case

conditions in all these cases, the actual system is almost

never operated at worst−case conditions. The alternative to

designing for the worst case is to use the dynamic TMIN

control function.

Dynamic TMIN 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 ADT7462 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

ambient temperature in a system 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

°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).

Obtaining the greatest benefit from the automatic fan

control mode involves characterizing 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 ADT7462 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.

Remote 1 and Remote 2 channels have dedicated operating

point registers. 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

ADT7462 dynamically alters the control solution to

maintain each zone temperature as close as possible to its

target operating point.

Figure 67 shows an overview of the parameters that affect

the operation of the dynamic TMIN control loop.

Figure 67. Dynamic TMIN Control Loop

TLOW TMIN OPERATING

POINT

THIGH

TRANGE

TEMPERATURE

TTHERM

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