ADT7473_11 ONSEMI [ON Semiconductor], ADT7473_11 Datasheet - Page 38

• Manufacturer Part Number: ADT7473_11
• Description: dbCOOL Remote Thermal Monitor and Fan Control
• Manufacturer: ONSEMI [ON Semiconductor]

Step 6: T
fan control occurs once the programmed T
is exceeded. T
value, that is, a T
PWM
effective T
following procedure:
PWM
remains the same. The higher the PWM
smaller the effective T
Figure 56. T
T
The T
Figure 57 shows how adjusting PWM
T
RANGE
RANGE
1. Determine the maximum operating temperature for
2. Determine experimentally the fan speed (PWM
3. Determine the slope of the required control loop to
4. Graphically program and visualize this
Figure 57. Adjusting PWM
MIN
MIN
that channel (for example, 70°C).
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).
meet these requirements.
functionality using the ADT7473/ADT7473−1
evaluation software.
PWM
RANGE
100%
RANGE
100%
50%
33%
= 33%. If PWM
is changed, T
0%
RANGE
is the range of temperature over which automatic
MIN
is implemented as a slope, which means that as
0%
RANGE
RANGE
or fan control slope is determined by the
for Temperature Channels
changes. Refer to Figure 56.
RANGE
T
MIN
is a temperature slope, not an arbitrary
T
Parameter Affects Cooling Slope
MIN
RANGE
RANGE
MIN
of 40°C holds true only for
, that is, the fan reaches full
305C
is increased or decreased, the
changes, but the actual slope
MIN
405C
T
RANGE
TEMPERATURE
Affects T
MIN
MIN
affects T
MIN
RANGE
temperature
value, the
RANGE
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.
38
speed (100%) at a lower temperature. Figure 58 shows how
increasing PWM
fan runs at full speed for different PWM
easily calculated as follows:
T
T
Max DC is the maximum duty cycle (100%) = 255 decimal.
Min DC is equal to PWM
T
Example 1
PWM
T
T
T
T
Example 2
40°C, and PWM
T
T
T
T
Example 3
40°C, and PWM
T
T
T
T
MAX
MIN
RANGE
MAX
MAX
MAX
MAX
MAX
MAX
MAX
MAX
MAX
MAX
MAX
MAX
For a given T
Calculate T, given that T
Calculate T
Calculate T
Figure 58. Increasing PWM
T
where:
MIN
MAX
is the temperature at which the fan turns on.
is the temperature at which the fan runs full speed.
= T
= 30°C + (100% − 10%) x 40°C/170
= 30°C + (255 − 26) x 40°C/170
= 84°C (effective T
= T
= 30°C + (100% − 25%) x 40°C/170
= 30°C + (255 − 64) x 40°C/170
= 75°C (effective T
= T
= 30°C + (100% − 33%) x 40°C/170
= 30°C + (255 − 85) x 40°C/170
= 70°C (effective T
is the duty PWM duty cycle vs. temperature slope.
100%
50%
33%
25%
10%
MIN
MIN
MIN
= 10% duty cycle = 26 (decimal).
0%
= T
MAX
MAX
MIN
+ (Max DC − Min DC) x T
+ (Max DC − Min DC) x T
+ (Max DC − Min DC) x T
RANGE
MIN
MIN
MIN
T
MIN
, given that T
, given that T
+ (Max DC − Min DC) x T
= 25% duty cycle = 64 (decimal).
= 33% duty cycle = 85 (decimal).
changes the effective T
value, the temperature at which the
T
MIN
MIN
RANGE
RANGE
RANGE
RANGE
305C
.
= 30°C, T
405C
MIN
455C
MIN
MIN
= 54°C)
= 45°C)
= 40°C)
545C
Changes Effective
= 30°C, T
= 30°C, T
RANGE
MIN
RANGE
RANGE
RANGE
RANGE
values can be
RANGE
= 40°C, and
RANGE
RANGE
/170
/170
/170
.
/170
=
=