ADT7476
Rev. B | Page 46 of 72
STEP 6: T
RANGE
FOR TEMPERATURE CHANNELS
T
RANGE
is the range of temperature over which automatic fan
control occurs once the programmed T
MIN
temperature has
been exceeded. T
RANGE
is the temperature range between
PWM
MIN
and 100% PWM where the fan speed changes linearly.
Otherwise stated, it is the line drawn between the T
MIN
/PWM
MIN
and the (T
MIN
+ T
RANGE
)/PWM 100% intersection points.
TEMPERATURE
T
MIN
100%
PWM
MIN
0%
P
W
M DUTY
CY
CLE
T
RANGE
05382-058
Figure 57. T
RANGE
Parameter Affects Cooling Slope
The T
RANGE
is determined by the following procedure:
1.
Determine the maximum operating temperature for the
channel (for example, 70°C).
2.
Determine experimentally the fan speed (PWM duty cycle
value) that does not exceed the temperature at the worst-
case operating points. For example, 70°C is reached when
the fans are running at 50% PWM duty cycle.
3.
Determine the slope of the required control loop to meet
these requirements.
4.
Using the ADT7476 evaluation software, graphically
program and visualize this functionality. Ask your local
Analog Devices, Inc. representative for details.
As PWM
MIN
is changed, the automatic fan control slope changes.
T
MIN
100%
33%
0%
P
W
M
DU
T
Y
C
Y
CL
E
50%
30°C
05
38
2-
0
59
Figure 58. Adjusting PWM
MIN
Changes the Automatic Fan Control Slope
As T
RANGE
is changed, the slope changes. As T
RANGE
gets smaller,
the fans reach 100% speed with a smaller temperature change.
05
38
2-
0
60
T
MIN
T
MIN–HYST
100%
0%
P
W
M
DUT
Y
CY
C
L
E
30°C
40°C
10%
45°C
54°C
Figure 59. Increasing T
RANGE
Changes the AFC slope
05382-061
100%
MAX
PWM
0%
P
W
M DUTY
CY
CLE
T
RANGE
10%
T
MIN–HYST
Figure 60. Changing PWM
MAX
Does Not Change the AFC Slope
Selecting T
RANGE
The T
RANGE
value can be selected for each temperature channel:
Remote 1, local, and Remote 2 temperature. Bits [7:4] (T
RANGE
)
of Register 0x5F to Register 0x61 define the T
RANGE
value for
each temperature channel.
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