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100
90
80
70
60
50
40
30
20
10
0
0
20
100
90
80
70
60
50
40
30
20
10
0
0
20
Figure 62. T
Example: Determining T
Channel
The following example shows how the different T
T
settings can be applied to three different thermal
RANGE
zones. In this example, the following T
T
= 80°C for ambient temperature
RANGE
T
= 53.33°C for CPU temperature
RANGE
T
= 40°C for VRM temperature
RANGE
This example uses the mux configuration described in
Step 2 - Configuring the Mux with the ADT7476A
connected as shown in Figure 52. Both CPU temperature
and VRM temperature drive the CPU fan connected to
PWM1. Ambient temperature drives the front chassis fan
and rear chassis fan connected to PWM2 and PWM3. The
front chassis fan is configured to run at PWM
The rear chassis fan is configured to run at PWM
The CPU fan is configured to run at PWM
Note: The control range for 4-wire fans is much wider than
that of 3-wire fans. In many cases, 4-wire fans can start with
a PWM drive of as little as 20% or less. In extreme cases,
some 3-wire fans cannot run unless a PWM drive of 60% or
more is applied.
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40
60
80
100
TEMPERATURE ABOVE T
MIN
40
60
80
100
TEMPERATURE ABOVE T
MIN
and % Fan Speed Slopes with
RANGE
PWM
= 20%
MIN
for Each Temperature
RANGE
RANGE
MIN
ADT7476A
25C
100
2.55C
90
3.335C
45C
80
55C
70
6.675C
85C
60
105C
50
13.35C
165C
40
205C
30
26.65C
325C
20
405C
10
53.35C
805C
0
120
0
25C
100
2.55C
90
3.335C
45C
80
55C
70
6.675C
85C
60
105C
50
13.35C
165C
40
205C
30
26.65C
325C
20
405C
10
53.35C
805C
0
120
0
Figure 63. T
Ambient, and CPU Temperature Channels
Step 7 − T
T
THERM
and
on a temperature channel. Above this temperature, a
MIN
component such as the CPU or VRM can operate beyond its
values apply:
safe operating limit. When the temperature measured
exceeds T
cycle (full speed) to provide critical system cooling.
The fans remain running at 100% until the temperature
drops below T
the number programmed into the hysteresis registers (0x6D
and 0x6E). The default hysteresis value is 4°C.
The T
THERM
worst-case operating temperature of the system. Because
exceeding any T
very negative acoustic effects. Ultimately, this limit should
be set up as a fail-safe, and users should ensure that it is not
= 20%.
MIN
exceeded under normal system operating conditions.
= 30%.
MIN
Note: T
= 10%.
THERM
speed no matter how automatic fan control settings are
configured. This allows some flexibility, because a T
value can be selected based on its slope, while a hard limit
(such as 70°C), can be programmed as T
temperature at which the fan reaches full speed) by setting
T
to that limit (for example, 70°C).
THERM
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44
VRM TEMP.
CPU TEMPERATURE
AMBIENT TEMPERATURE
10
20
30
40
50
60
TEMPERATURE ABOVE T
VRM TEMP.
CPU TEMPERATURE
AMBIENT TEMPERATURE
10
20
30
40
50
60
TEMPERATURE ABOVE T
and % Fan Speed Slopes for VRM,
RANGE
for Temperature Channels
THERM
is the absolute maximum temperature allowed
, all fans are driven at 100% PWM duty
THERM
minus hysteresis, where hysteresis is
THERM
limit should be considered the maximum
limit runs all fans at 100%, it has
THERM
limits are nonmaskable and affect the fan
70
80
90
100
MIN
70
80
90
100
MIN
RANGE
(the
MAX
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