ADM1030ARQ-REEL View Datasheet(PDF) - ON Semiconductor
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ADM1030ARQ-REEL Datasheet PDF : 29 Pages
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ADM1030
AUTOMATIC FAN SPEED CONTROL
The ADM1030 has a local temperature channel and a remote
temperature channel, which may be connected to an on-chip
diode-connected transistor on a CPU. These two temperature
channels may be used as the basis for an automatic fan speed
control loop to drive a fan using Pulsewidth Modulation (PWM).
HOW DOES THE CONTROL LOOP WORK?
The Automatic Fan Speed Control Loop is shown in Fig-
ure 6 below.
MAX
SPIN UP FOR 2 SECONDS
FAN
SPEED
MIN
TMIN
TMAX = T MIN + T RANGE
TEMPERATURE
Figure 6. Automatic Fan Speed Control
In order for the fan speed control loop to work, certain loop
parameters need to be programmed into the device.
1. TMIN. The temperature at which the fan should switch on
and run at minimum speed. The fan will only turn on once
the temperature being measured rises above the TMIN value
programmed. The fan will spin up for a predetermined time
(default = 2 secs). See Fan Spin-Up section for more details.
2. TRANGE. The temperature range over which the ADM1030
will automatically adjust the fan speed. As the temperature
increases beyond TMIN, the PWM_OUT duty cycle will be
increased accordingly. The TRANGE parameter actually defines
the fan speed versus temperature slope of the control loop.
3. TMAX. The temperature at which the fan will be at its maxi-
mum speed. At this temperature, the PWM duty cycle
driving the fan will be 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.
4. A hysteresis value of 5rC is included in the control loop to
prevent the fan continuously switching on and off if the tem-
perature is close to TMIN. The fan will continue to run until
such time as the temperature drops 5rC below TMIN.
Figure 7 shows the different control slopes determined by the
TRANGE value chosen, and programmed into the ADM1030.
TMIN was set to 0rC to start all slopes from the same point. It
can be seen how changing the TRANGE value affects the PWM
duty cycle versus temperature slope.
100
93
87
80
73
66
60
53
47
40
33
0 5 10
TMIN
= 80�C
T RANGE
20
40
60
80
TMAX = T MIN + TRANGE
TEMPERATURE – �C
Figure 7. PWM Duty Cycle vs. Temperature Slopes (TRANGE)
Figure 8 shows how, for a given TRANGE, changing the TMIN
value affects the loop. Increasing the TMIN value will increase
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 may be changed in increments of 4rC.
100
93
87
80
73
66
60
53
47
40
33
0
TMIN
20
40
60
80
TMAX = T MIN + T RANGE
TEMPERATURE – �C
Figure 8. Effect of Increasing TMIN Value on Control Loop
FAN SPIN-UP
As was previously mentioned, once the temperature being mea-
sured exceeds the TMIN value programmed, the fan will turn on
at minimum speed (default = 33% duty cycle). However, the
problem with fans being driven by PWM is that 33% duty cycle
is not enough to reliably start the fan spinning. The solution is
to spin the fan up for a predetermined time, and once the fan
has spun up, its running speed may be reduced in line with the
temperature being measured.
The ADM1030 allows fan spin-up times between 200 ms and
8 seconds. Bits <2:0> of Fan Characteristics Register 1 (Register
0x20) program the fan spin-up time.
Rev. 2 | Page 12 of 29 | www.onsemi.com
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