ADM1031ARQZ Просмотр технического описания (PDF) - ON Semiconductor
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ADM1031ARQZ Datasheet PDF : 30 Pages
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ADM1031
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 = TMAX). The PWM duty cycle
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.
100
93
87
80
73
66
60
53
47
40
33
0
TRANGE = 40°C
20
TMIN
40
60
TMAX = TMIN + TRANGE
LOCAL TEMPERATURE ( °C)
Figure 24. Maximum Speed Calculated by Local
Temperature Control Loop Drives Fan
100
93
87
80
73
66
60
53
47
40
33
0
TMIN
TRANGE = 80°C
20
40
70
80
TMAX = TMIN + TRANGE
REMOTE TEMPERATURE ( °C)
Figure 25. Maximum Speed Calculated by Local
Temperature Control Loop Drives Fan
Programming the Automatic Fan Speed Control Loop
1. Program a value for TMIN.
2. Program a value for the slope TRANGE.
3. TMAX = TMIN + TRANGE.
4. Program a value for fan spin−up time.
5. Program the desired automatic fan speed control
mode behavior, that is, which temperature channel
controls the fan.
6. Select automatic fan speed control mode by setting
Bit 7 of Configuration Register 1.
Other Control Loop Parameters
It should be noted that changing the minimum PWM duty
cycle affects the control loop behavior.
Slope 1 of Figure 26 shows TMIN set to 0°C and the
TRANGE chosen is 40°C. In this case, the fan’s PWM duty
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 TMIN is changed, its effect can be seen
on Slope 2 and Slope 3. Take Case 2, where the minimum
PWM duty cycle is reprogrammed from 33% (default) to
53%.
100
93
87
80
3
73
2
66
60
1
53
47
40
33
0
TMIN
TRANGE = 40°C
16
28
40
60
TEMPERATURE (°C)
Figure 26. Effect of Changing Minimum Duty Cycle
on Control Loop with Fixed TMIN and TRANGE Values
The fan actually reaches full speed at a much lower
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
TMIN and fixed TRANGE, is that the fan actually reaches full
speed (TMAX) at a lower temperature than TMIN + TRANGE.
How can TMAX be calculated?
In automatic fan speed control mode, the register that
holds the minimum PWM duty cycle at TMIN, is the fan
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.
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