ADT7476ARQZ-R7 datasheet(38/67 Pages) ONSEMI

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ADT7476

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Step 3—TMIN Settings for Thermal Calibration

Channels

TMIN is the temperature at which the fans start to turn on

under automatic fan control. The speed at which the fan runs

at TMIN is programmed later. The TMIN values chosen are

temperature channel specific, for example, 25

°C for

ambient channel, 30

°C for VRM temperature, and 40°C for

processor temperature.

TMIN is an 8−bit value, either twos complement or Offset

64, which can be programmed in 1

°C increments. A TMIN

channel: Remote 1, local, and Remote 2 temperature. Once

the TMIN value is exceeded, the fan turns on and runs at the

minimum PWM duty cycle. The fan turns off once the

temperature has dropped below TMIN − THYST.

To overcome fan inertia, the fan is spun up until two valid

TACH rising edges are counted. See the Fan Startup

Timeout section for more details. In some cases, primarily

for psycho−acoustic reasons, it is desirable that the fan never

switch off below TMIN. Setting Bits [7:5] of Enhance

Acoustics Register 1 (0x62) keeps the fans running at the

PWM minimum duty cycle if the temperature should fall

below TMIN.

TMIN Registers

Enhance Acoustics Register 1 (0x62)

Bit 7 (MIN3) = 0, PWM3 is off (0% PWM duty cycle) when

temperature is below TMIN – THYST.

Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty

cycle below TMIN – THYST.

Bit 6 (MIN2) = 0, PWM2 is off (0% PWM duty cycle) when

temperature is below TMIN – THYST.

Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty

cycle below TMIN – THYST.

Bit 5 (MIN1) = 0, PWM1 is off (0% PWM duty cycle) when

temperature is below TMIN – THYST.

Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty

cycle below TMIN – THYST.

Figure 53. Understanding the TMIN Parameter

100%

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

PWM

MIN

PWM

MIN

PWM

MIN

100%

PWM

GENERATOR

PWM

GENERATOR

TACHOMETER 3

AND 4

MEASUREMENT

TACHOMETER 1

MEASUREMENT

TACHOMETER 2

MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

PWM

GENERATOR

PWM

CONFIG

PWM

CONFIG

PWM

CONFIG

ADT7476ARQZ-R7 데이터시트(PDF) 38 Page - ON Semiconductor

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