ADT7476A
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40
Step 3 − T
MIN
Settings for Thermal Calibration
Channels
T
MIN
is the temperature at which the fans start to turn on
under automatic fan control. The speed at which the fan runs
at T
MIN
is programmed later. The T
MIN
values chosen are
temperature channel specific, for example, 25
°
C for
ambient channel, 30
°
C for VRM temperature, and 40
°
C for
processor temperature.
T
MIN
is an 8-bit value, either twos complement or Offset
64, which can be programmed in 1
°
C increments. A T
MIN
register is associated with each temperature measurement
channel: Remote 1, local, and Remote 2 temperature. Once
the T
MIN
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 T
MIN
− T
HYST
.
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 T
MIN
. 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 T
MIN
.
Table 44. T
MIN
REGISTERS
Register
Description
Default
0x67
Remote 1 Temperature T
MIN
0x5A (90
°
C)
0x68
Local Temperature T
MIN
0x5A (90
°
C)
0x69
Remote 2 Temperature T
MIN
0x5A (90
°
C)
Enhance Acoustics Register 1 (0x62)
Bit 7 (MIN3) = 0, PWM3 is off (0% PWM duty cycle) when
temperature is below T
MIN
– T
HYST
.
Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty
cycle below T
MIN
– T
HYST
.
Bit 6 (MIN2) = 0, PWM2 is off (0% PWM duty cycle) when
temperature is below T
MIN
– T
HYST
.
Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty
cycle below T
MIN
– T
HYST
.
Bit 5 (MIN1) = 0, PWM1 is off (0% PWM duty cycle) when
temperature is below T
MIN
– T
HYST
.
Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty
cycle below T
MIN
– T
HYST
.
Figure 53. Understanding the T
MIN
Parameter
THERMAL CALIBRATION
REMOTE1 =
AMBIENT TEMP
100%
0%
T
MIN
T
RANGE
PWM
MIN
MUX
S
TACHOMETER1
MEASUREMENT
S
S
PWM
MIN
PWM
MIN
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
LOCAL =
VRM TEMP
REMOTE2 =
CPU TEMP
TACHOMETER2
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER3
AND 4
MEASUREMENT
PWM
CONFIG
PWM
GENERATOR
PWM1
PWM2
PWM3
TACH3
TACH2
TACH1
CPU FAN SINK
FRONT CHASSIS
REAR CHASSIS
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
CONFIG
PWM
GENERATOR
PWM
CONFIG
PWM
GENERATOR
T
MIN
100%
0%
PWM DUTY CYCLE
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