ADT7490ARQZ-R7 datasheet(35/75 Pages) ONSEMI

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ADT7490

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Automatic Fan Control Multiplexer Options

Bits [7:5] (BHVR), Register 0x5C, Register 0x5D, and

000 = Remote 1 temperature controls PWMx

001 = Local temperature controls PWMx

010 = Remote 2 temperature controls PWMx

101 = Fastest speed calculated by local and Remote 2

temperature controls PWMx

110 = Fastest speed calculated by all three temperature

channels controls PWMx

The fastest speed calculated options pertain to controlling

one PWM output based on multiple temperature channels.

The thermal characteristics of the three temperature zones

can be set to drive a single fan. An example is the fan turning

on when the Remote 1 temperature exceeds 60

°C or if

the local temperature exceeds 45

°C.

Setting the ALT bit in Register 0x5C, Register 0x5D, and

[7:5] of the PWM configuration registers.

Bits [7:5] (BHVR), Register 0x5C, Register 0x5D, and

000 = PECI0 reading controls PWMx

001 = PECI1 reading controls PWMx

010 = PECI2 reading controls PWMx

011 = PECI3 reading controls PWMx

101 = Fastest speed calculated by all four PECI

readings controls PWMx

111 = Fastest speed calculated by all thermal zones

(Local, Rem1, Rem2 and PECI) controls PWMx

Other Mux Options

Bits [7:5] (BHVR), Register 0x5C, Register 0x5D, and

011 = PWMx runs full speed

100 = PWMx disabled (default)

111 = Manual mode. PWMx is running under software

control. In this mode, PWM duty cycle registers

(Register 0x30 to Register 0x32) are writable and

control the PWM outputs.

Bits [7:5] (BHVR), Register 0x5C, Register 0x5D, and

100 = PWMx runs at 100% duty cycle

110 = PWMx runs at 100% duty cycle

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, that can be programmed in 1

°C increments. A TMIN

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

When 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. When set, Bits [7:5] of Enhanced

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

PWM minimum duty cycle if the temperature should fall

below TMIN.

TMIN Registers

Enhanced Acoustics Register 1 (Register 0x62)

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

the 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

the 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

the temperature is below TMIN – THYST.

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

cycle below TMIN – THYST.

ADT7490ARQZ-R7 Datasheet(PDF) 35 Page - ON Semiconductor

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