ADT7467ARQZ-R7 datasheet(38/77 Pages) ONSEMI

38 / 77 page

ADT7467

Rev. 3 | Page 38 of 77 | www.onsemi.com

PROGRAMMING THE AUTOMATIC FAN SPEED CONTROL LOOP

To more efficiently understand the automatic fan speed control

loop, it is strongly recommended to use the ADT7467

evaluation board and software while reading this section.

This section provides the system designer with an understand-

ing of the automatic fan control loop and provides step-by-step

guidance on effectively evaluating and selecting critical system

parameters. To optimize the system characteristics, the designer

should consider several aspects of the system configuration,

including the number of fans, where fans are located, and what

temperatures are measured.

The mechanical or thermal engineer who is tasked with the

system thermal characterization should also be involved at the

beginning of the process.

STEP 1: HARDWARE CONFIGURATION

The motherboard sensing and control capabilities should be

addressed in the early stages of designing a system, and

decisions about how these capabilities are used should involve

the system’s thermal/mechanical engineer. Ask the following

questions:

What ADT7467 functionality will be used?

• PWM2 or SMBALERT

• TACH4 fan speed measurement or overtemperature

THERM function

• 5 V voltage monitoring or overtemperature THERM

function

• 12 V voltage monitoring or VID5 input

The ADT7467 offers multifunctional pins that can be

reconfigured to suit different system requirements and

physical layouts. These multifunction pins are software

programmable.

How many fans will be supported in the system, three or

four? This influences the choice of whether to use the

TACH4 pin or to reconfigure it for the THERM function.

Will the CPU fan be controlled using the ADT7467, or will

it run at full speed 100% of the time?

Running it at 100% frees up a PWM output, but the system

is louder.

Where will the ADT7467 be physically located in the

system?

This influences the assignment of the temperature measure-

ment channels to particular system thermal zones. For

example, locating the ADT7467 close to the VRM controller

circuitry allows the VRM temperature to be monitored

using the local temperature channel.

REAR CHASSIS

FRONT CHASSIS

CPU FAN SINK

REMOTE 1 =

AMBIENT TEMP

LOCAL =

VRM TEMP

REMOTE 2 =

CPU TEMP

PWM1

PWM2

TACH1

TACH2

TACH3

PWM3

MUX

THERMAL CALIBRATION

TMIN

TRANGE

THERMAL CALIBRATION

100%

TMIN

TRANGE

THERMAL CALIBRATION

100%

TMIN

TRANGE

TACHOMETER 1

MEASUREMENT

PWM

CONFIG

PWM

MIN

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

PWM

GENERATOR

TACHOMETER 2

MEASUREMENT

PWM

CONFIG

PWM

MIN

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

PWM

GENERATOR

TACHOMETER 3

AND 4

MEASUREMENT

PWM

CONFIG

PWM

MIN

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

PWM

GENERATOR

100%

Figure 53. Hardware Configuration Example

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