EVAL-ADM1031EB ON Semiconductor, EVAL-ADM1031EB Datasheet - Page 14

• Manufacturer Part Number: EVAL-ADM1031EB
• Description: BOARD EVAL FOR ADM1031
• Manufacturer: ON Semiconductor
• Type: Temperature Sensorr

Specifications of EVAL-ADM1031EB

• Contents: Evaluation Board
• For Use With/related Products: ADM1031
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

temperature measuring 60°C while the Remote 1
temperature is measuring 70°C. The PWM duty cycle
calculated by the local temperature control loop is 100%
(because the temperature = T
calculated by the Remote 1 temperature control loop at 70°C
is approximately 90%. Therefore, the fan runs full−speed
(100% duty cycle). Remember, that the fan speed is based on
the fastest speed calculated, and is not necessarily based on
the highest temperature measured. Depending on the control
loop parameters programmed, a lower temperature on one
channel, can actually calculate a faster speed than a higher
temperature on the other channel.
Figure 24. Maximum Speed Calculated by Local
Figure 25. Maximum Speed Calculated by Local
100
100
93
87
80
73
66
60
53
47
40
33
93
87
80
73
66
60
53
47
40
33
T
MIN
0
0
Temperature Control Loop Drives Fan
Temperature Control Loop Drives Fan
T
MIN
20
20
REMOTE TEMPERATURE ( °C)
LOCAL TEMPERATURE ( °C)
40
40
MAX
). The PWM duty cycle
T
T
MAX
RANGE
60
T
= T
T
RANGE
MAX
= 80°C
MIN
70
= T
+ T
= 40°C
MIN
RANGE
80
+ T
http://onsemi.com
RANGE
14
Programming the Automatic Fan Speed Control Loop
Other Control Loop Parameters
cycle affects the control loop behavior.
T
cycle varies over the range 33% to 100%. The fan runs
full−speed at 40°C. If the minimum PWM duty cycle at
which the fan runs at T
on Slope 2 and Slope 3. Take Case 2, where the minimum
PWM duty cycle is reprogrammed from 33% (default) to
53%.
temperature, 28°C. Case 3 shows that when the minimum
PWM duty cycle is increased to 73%, the temperature at
which the fan runs full speed is 16°C. Therefore, the effect
of increasing the minimum PWM duty cycle, with a fixed
T
speed (T
How can T
holds the minimum PWM duty cycle at T
speed configuration register (Register 0×22). Table 7 shows
the relationship between the decimal values written to the
fan speed configuration register and PWM duty cycle
obtained.
RANGE
MIN
on Control Loop with Fixed T
It should be noted that changing the minimum PWM duty
Slope 1 of Figure 26 shows T
The fan actually reaches full speed at a much lower
In automatic fan speed control mode, the register that
Figure 26. Effect of Changing Minimum Duty Cycle
1. Program a value for T
2. Program a value for the slope T
3. T
4. Program a value for fan spin−up time.
5. Program the desired automatic fan speed control
6. Select automatic fan speed control mode by setting
and fixed T
mode behavior, that is, which temperature channel
controls the fan.
Bit 7 of Configuration Register 1.
MAX
MAX
chosen is 40°C. In this case, the fan’s PWM duty
MAX
) at a lower temperature than T
= T
100
be calculated?
93
87
80
73
66
60
53
47
40
33
T
RANGE
MIN
MIN
0
3
+ T
MIN
, is that the fan actually reaches full
2
RANGE
is changed, its effect can be seen
16
MIN
1
.
MIN
.
TEMPERATURE (°C)
MIN
28
and T
RANGE
set to 0°C and the
RANGE
MIN
MIN
40
T
.
RANGE
, is the fan
+ T
Values
RANGE
= 40°C
60
.