ADT7467ARQZ-R7 datasheet(49/77 Pages) ONSEMI

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ADT7467

Rev. 3 | Page 49 of 77 | www.onsemi.com

STEP 8: THYST FOR TEMPERATURE CHANNELS

THYST is the amount of extra cooling a fan provides after the

temperature measured drops below TMIN before the fan turns

off. The premise for temperature hysteresis (THYST) is that,

without it, the fan would merely chatter or cycle on and off

repeatedly whenever the temperature hovered near the TMIN

setting.

The THYST value determines the amount of time needed for the

system to cool down or heat up as the fan turns on and off.

Values of hysteresis are programmable in the range 1°C to 15°C.

Larger values of THYST prevent the fans from chattering on and

off. The THYST default value is set at 4°C.

The THYST setting not only applies to the temperature hysteresis

for fan on/off, but also is used for the TTHERM hysteresis value,

as described in Step 6: TRANGE for Temperature Channels. There-

fore, programming Register 0x6D and Register 0x6E sets the

hysteresis for both fan on/off and the THERM function.

Hysteresis Registers

<7:4>, Remote 1 temperature hysteresis (4°C default)

<3:0>, local temperature hysteresis (4°C default)

<7:4>, Remote 2 temperature hysteresis (4°C default)

In some applications, it is required that fans continue to run at

PWMMIN, instead of turning off when the temperature drops

below TMIN. Bits <7:5> of Enhanced Acoustics Register 1

(0x62) allow the fans to be either turned off or kept spinning

below TMIN. If the fans are always on, the THYST value has no

effect on the fan when the temperature drops below TMIN.

REAR CHASSIS

FRONT CHASSIS

CPU FAN SINK

LOCAL =

VRM TEMP

PWM1

PWM2

TACH1

TACH2

TACH3

PWM3

REMOTE 1 =

AMBIENT TEMP

REMOTE 2 =

CPU TEMP

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%

TMIN

100%

TRANGE

TTHERM

Figure 68. The THYST Value Applies to Fan On/Off Hysteresis and THERM Hysteresis

ADT7467ARQZ-R7 Datasheet(PDF) 49 Page - ON Semiconductor

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