ADM1031(2012) データシートの表示（PDF） - ON Semiconductor
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ADM1031 Datasheet PDF : 32 Pages
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ADM1031
How Does the Control Loop Work?
The automatic fan speed control loop is shown in
Figure 21.
MAX
SPIN-UP FOR 2 SECONDS
MIN
TMIN
TMAX = TMIN + TRANGE
TEMPERATURE
Figure 21. Automatic Fan Speed Control Loop
TMIN is the temperature at which the fan should switch on
and run at minimum speed. The fan only turns on once the
temperature being measured rises above the TMIN value
programmed. The fan spins up for a predetermined time
(default = 2 seconds). See the Fan Spin-Up section for more
details.
TRANGE is the temperature range over which the
ADM1031 automatically adjusts the fan speed. As the
temperature increases beyond TMIN, the PWM_OUT duty
cycle increases accordingly. The TRANGE parameter
actually defines the fan speed vs. temperature slope of the
control loop.
TMAX is the temperature at which the fan is at its
maximum speed. At this temperature, the PWM duty cycle
driving the fan is 100%. TMAX is given by TMIN + TRANGE.
Since this parameter is the sum of the TMIN and TRANGE
parameters, it does not need to be programmed into a register
on-chip.
A hysteresis value of 5C is included in the control loop
to prevent the fan continuously switching on and off if the
temperature is close to TMIN. The fan continues to run until
the temperature drops 5C below TMIN.
Figure 22 shows the different control slopes determined
by the TRANGE value chosen, and programmed into the
ADM1031. TMIN is set to 0C to start all slopes from the
same point. The figure shows how changing the TRANGE
value affects the PWM duty cycle vs. temperature slope.
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0 5 10 20
TMIN
TRANGE = 5C
TRANGE = 10C
TRANGE = 20C
TRANGE = 40C
TRANGE = 80C
40
60
80
TMAX = TMIN + TRANGE
TEMPERATURE (C)
Figure 22. PWM Duty Cycle vs. Temperature Slope
(TRANGE)
Figure 23 shows how, for a given TRANGE, changing the
TMIN value affects the loop. Increasing the TMIN value
increases the TMAX (temperature at which the fan runs full
speed) value, since TMAX = TMIN + TRANGE. Note, however,
that the PWM duty cycle vs. temperature slope remains
exactly the same. Changing the TMIN value merely shifts the
control slope. The TMIN can be changed in increments of 4C.
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60
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0
TMIN
TRANGE = 40C
20
40
60
80
T°MAX = TMIN + TRANGE
TEMPERATURE (C)
Figure 23. Effect of Increasing TMIN Value on
Control Loop
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