adm1027 Analog Devices, Inc., adm1027 Datasheet - Page 32

• Manufacturer Part Number: adm1027
• Description: Dbcool? Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

ADM1027
Step 5
Determine T
T
control occurs once the programmed T
been exceeded. T
an arbitrary value, i.e., a T
PWM
effective T
The T
procedure:
1. Determine the maximum operating temperature for that
2. Determine experimentally the fan speed (PWM duty cycle
3. Determine the slope of the required control loop to meet
4. Use best fit approximation to determine the most suitable
RANGE
channel, e.g., 70∞C.
value) will not exceed that temperature at the worst-case
operating points, e.g., 70∞C is reached when the fans are
running at 50% PWM duty cycle.
these requirements.
T
able to calculate the best fit value; ask your local Analog
Devices representative for more details.
Figure 32. T
RANGE
MIN
RANGE
is the range of temperature over which automatic fan
Figure 33. Adjusting PWM
PWM
= 33%. If PWM
RANGE
100%
value. There is ADM1027 evaluation software avail-
100%
50%
33%
0%
or fan control slope is determined by the following
RANGE
MIN
0%
is changed, as described later.
RANGE
RANGE
for Each Temperature Channel
T
Parameter Affects Cooling Slope
MIN
is actually a temperature slope and not
T
MIN
MIN
RANGE
is increased or decreased, the
of 40∞C only holds true for
30 C
40 C
T
MIN
RANGE
TEMPERATURE
MIN
Affects T
temperature has
RANGE
–32–
T
changed, T
same. The higher the PWM
T
lower temperature.
For a given T
will run full-speed for different PWM
calculated:
where:
T
T
MaxD.C. = Maximum duty cycle (100%) = 255 decimal
MinD.C. = PWM
T
Example: Calculate T
and PWM
T
Example: Calculate T
and PWM
T
T
T
T
T
T
T
MAX
MIN
RANGE
RANGE
RANGE
MAX
MAX
Figure 34. Increasing PWM
MAX
MAX
MAX
MAX
MAX
MAX
T
= Temperature at which the fan will turn on
= Temperature at which the fan runs full-speed
= 84
= 75∞C (effective T
MAX
=
=
=
=
=
=
= PWM duty cycle versus temperature slope
is implemented as a slope, which means as PWM
will be, i.e., the fan will reach full speed (100%) at a
30
30
30
T
T
30
MIN
MIN
MIN
∞
MIN
100%
=
C (effective T
∞
∞
∞
∞
RANGE
50%
33%
25%
10%
C
C
C
0%
C
T
RANGE
= 10% duty cycle = 26 decimal
= 25% duty cycle = 64 decimal
MIN
+
+
+
+
+
+
(
(
(
(
(
(
100
MIN
100
255 26
255 64
MaxD C
MaxD C
changes, but the actual slope remains the
+
value, the temperature at which the fan
(
%
%
MaxD.C. MinD.C.
T
-
-
MAX
MAX
MIN
-
-
. .
. .
RANGE
10
RANGE
, given T
, given T
25
)
)
MIN
¥
¥
-
%
-
%
40
40
MinD C
)
MinD C
30 C
MIN
)
value, the smaller the effective
-
¥
= 54
= 45∞C)
¥
∞
40 C
∞
C
C
40
45 C
Changes Effective T
40
MIN
MIN
170
170
∞
∞
54 C
. .
. .
∞
MIN
C)
C
C
= 30∞C, T
= 30∞C, T
)
)
170
170
¥
¥
values can easily be
)
T
T
¥
RANGE
RANGE
T
RANGE
RANGE
RANGE
170
170
170
REV. A
= 40∞C,
= 40∞C
RANGE
MIN
is