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