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REV. A

–30–

ADM1027

Step 3

Determine TMIN Setting for Each Thermal Channel

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

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

at TMIN is programmed later. The TMIN values chosen will be

temperature channel specific, e.g., 25

∞C for ambient channel,

∞C for VRM temperature, and 40∞C for processor temperature.

TMIN is an 8-bit twos complement value that can be pro-

grammed in 1

∞C increments. There is a TMIN register associated

with each temperature measurement channel, Remote 1, Local

and Remote 2 Temp. Once the TMIN value is exceeded, the fan

turns on and runs at minimum PWM duty cycle. The fan will

turn off once temperature has dropped below TMIN – THYST

(detailed later).

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

rising edges are counted. See the Fan Start-Up Timeout section

for more details. In some cases, primarily for psycho-acoustic

reasons, it is desirable that the fan never switches off below TMIN.

Bits <7:5> of Enhance Acoustics Register 1 (Reg. 0x62), when

set, keep the fans running at PWM minimum duty cycle should

the temperature be below TMIN.

TMIN Registers

Reg. 0x67 Remote 1 Temperature TMIN = 0x5A (90

∞C default)

Reg. 0x68 Local Temperature TMIN = 0x5A (90

∞C default)

Reg. 0x69 Remote 2 Temperature TMIN = 0x5A (90

∞C default)

Enhance Acoustics Reg 1 (Reg. 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.

TMIN

100%

TACHOMETER 1

MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT

TACHOMETER 2

MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT

TACHOMETERS 3

AND 4

MEASUREMENT

PWM

GENERATOR

PWM

GENERATOR

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT

PWM

GENERATOR

PWM

CONFIG

PWM

MIN

MUX

THERMAL CALIBRATION

100%

TMIN

TRANGE

THERMAL CALIBRATION

100%

TMIN

TRANGE

THERMAL CALIBRATION

100%

TMIN

TRANGE

PWM

MIN

PWM

MIN

PWM

CONFIG

PWM

CONFIG

REMOTE 1 =

AMBIENT TEMP

LOCAL =

VRM TEMP

REMOTE 2 =

CPU TEMP

PWM1

TACH1

CPU

FANSINK

FRONT

CHASSIS

REAR

CHASSIS

PWM3

TACH3

PWM2

TACH2

Figure 29. Understanding TMIN Parameter

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