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ADM1030ARQZ

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ADM1030
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13
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
Figure 21 below.
Figure 21. Automatic Fan Speed Control
TEMPERATURE
FAN SPEED
T
MIN
MIN
MAX
T
MAX
= T
MIN
+ T
RANGE
SPIN-UP FOR 2 SECONDS
In order for the fan speed control loop to work, certain
loop parameters need to be programmed into the device.
1. T
MIN
. 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 T
MIN
value programmed. The fan
will spin up for a predetermined time
(default = 2 secs). See Fan Spin-up section for
more details.
2. T
RANGE
. The temperature range over which the
ADM1030 will automatically adjust the fan speed.
As the temperature increases beyond T
MIN
, the
PWM_OUT duty cycle will be increased
accordingly. The T
RANGE
parameter actually
defines the fan speed versus temperature slope of
the control loop.
3. T
MAX
. The temperature at which the fan will be at
its maximum speed. At this temperature, the PWM
duty cycle driving the fan will be 100%. T
MAX
is
given by T
MIN
+ T
RANGE
. Since this parameter is
the sum of the T
MIN
and T
RANGE
parameters, it
does not need to be programmed into a register
on-chip.
4. 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 T
MIN
. The fan
will continue to run until such time as the
temperature drops 5C below T
MIN
.
Figure 22 shows the different control slopes determined
by the T
RANGE
value chosen, and programmed into the
ADM1030. T
MIN
was set to 0C to start all slopes from the
same point. It can be seen how changing the T
RANGE
value
affects the PWM duty cycle versus temperature slope.
33
40
47
53
60
66
73
80
87
93
100
Figure 22. PWM Duty Cycle vs. Temperature
Slopes (T
RANGE
)
TEMPERATURE (C)
PWM DUTY CYCLE (%)
T
MAX
= T
MIN
+ T
RANGE
T
MIN
0 5 10 20 40 60 80
A
B
C
D
E
A − T
RANGE
= 5C
B − T
RANGE
= 10C
C − T
RANGE
= 20C
D − T
RANGE
= 40C
E − T
RANGE
= 80C
Figure 23 shows how, for a given T
RANGE
, changing the
T
MIN
value affects the loop. Increasing the T
MIN
value will
increase the T
MAX
(temperature at which the fan runs full
speed) value, since T
MAX
= T
MIN
+ T
RANGE
. Note,
however, that the PWM Duty Cycle vs Temperature slope
remains exactly the same. Changing the T
MIN
value merely
shifts the control slope. The T
MIN
may be changed in
increments of 4C.
33
40
47
53
60
66
73
80
87
93
100
Figure 23. Effect of Increasing T
MIN
Value
on Control Loop
TEMPERATURE (C)
PWM DUTY CYCLE (%)
T
MAX
= T
MIN
+ T
RANGE
T
MIN
02040 6080
T
RANGE
= 40C
Fan Spin-up
As was previously mentioned, once the temperature being
measured exceeds the T
MIN
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
ADM1030
http://onsemi.com
14
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.
Table 9. FAN SPIN-UP TIMES
Bits 2:0
Spin-up Times
(Fan Characteristics Register 1)
000 200 ms
001 400 ms
010 600 ms
011 800 ms
100 1 sec
101 2 sec (Default)
110 4 sec
111 8 sec
Once the Automatic Fan Speed Control Loop parameters
have been chosen, the ADM1030 device may be
programmed. The ADM1030 is placed into Automatic Fan
Speed Control Mode by setting Bit 7 of Configuration
Register 1 (Register 0x00). The device powers up into
Automatic Fan Speed Control Mode by default. The control
mode offers further flexibility in that the user can decide
which temperature channel/channels control the fan.
Table 10. AUTO MODE FAN BEHAVIOR
Bits 6, 5 Control Operation (Config Register 1)
00 Remote Temperature Controls the Fan
11 Maximum Speed Calculated by Local and
Remote Temperature Channels Control the Fan
When Bits 5 and 6 of Config Register 1 are both set to 1,
it offers increased flexibility. The local and remote
temperature channels can have independently programmed
control loops with different control parameters. Whichever
control loop calculates the fastest fan speed based on the
temperature being measured, drives the fan.
Figures 24 and 25 show how the fan’s PWM duty cycle is
determined by two independent control loops. This is the
type of Auto Mode Fan Behavior seen when Bits 5 and 6 of
Config Register 1 are set to 11. Figure 24 shows the control
loop for the Local Temperature channel. Its T
MIN
value has
been programmed to 20C, and its T
RANGE
value is 40C.
The local temperature’s T
MAX
will thus be 60C. Figure 25
shows the control loop for the Remote Temperature channel.
Its T
MIN
value has been set to 0C, while its
T
RANGE
=80C. Therefore, the Remote Temperature’s
T
MAX
value will be 80C.
Consider if both temperature channels measure 40C.
Both control loops will calculate a PWM duty cycle of 66%.
Therefore, the fan will be driven at 66% duty cycle.
If both temperature channels measure 20C, the local
channel will calculate 33% PWM duty cycle, while the
remote channel will calculate 50% PWM duty cycle. Thus,
the fan will be driven at 50% PWM duty cycle. Consider the
local temperature measuring 60C while the remote
temperature is measuring 70C. The PWM duty cycle
calculated by the local temperature control loop will be
100% (since the temperature = T
MAX
). The PWM duty
cycle calculated by the remote temperature control loop at
70C will be approximately 90%. So the fan will run
full-speed (100% duty cycle). Remember, that the fan speed
will be 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, may actually calculate a
faster speed, than a higher temperature on the other channel.
33
40
47
53
60
66
73
80
87
93
100
Figure 24. Max Speed Calculated by Local
Temperature Control Loop Drives Fan
LOCAL TEMPERATURE (C)
PWM DUTY CYCLE (%)
T
MAX
= T
MIN
+ T
RANGE
T
MIN
02040 60
T
RANGE
= 40C
Figure 25. Max Speed Calculated by Remote
Temperature Control Loop Drives Fan
33
40
47
53
60
66
73
80
87
93
100
PWM DUTY CYCLE (%)
REMOTE TEMPERATURE (C)
T
MAX
= T
MIN
+ T
RANGE
T
MIN
02040 7080
ADM1030
http://onsemi.com
15
Programming the Automatic Fan Speed Control
Loop
1. Program a value for T
MIN
.
2. Program a value for the slope T
RANGE
.
3. T
MAX
= T
MIN
+ T
RANGE
.
4. Program a value for Fan Spin-up Time.
5. Program the desired Automatic Fan Speed Control
Mode Behavior, i.e., 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
Having programmed all the above loop parameters, are
there any other parameters to worry about?
T
MIN
was defined as being the temperature at which the
fan switched on and ran at minimum speed. This minimum
speed is 33% duty cycle by default. If the minimum PWM
duty cycle is programmed to 33%, the fan control loops will
operate as previously described.
It should be noted however, that changing the minimum
PWM duty cycle affects the control loop behavior.
Slope 1 of Figure 26 shows T
MIN
set to 0C and the
T
RANGE
chosen is 40C. In this case, the fan’s PWM duty
cycle will vary over the range 33% to 100%. The fan will run
full-speed at 40C. If the minimum PWM duty cycle at
which the fan runs at T
MIN
is changed, its effect can be seen
on Slopes 2 and 3. Take Case 2, where the minimum PWM
duty cycle is reprogrammed from 33% (default) to 53%.
33
40
53
60
73
80
87
93
100
Figure 26. Effect of Changing Minimum Duty Cycle
on Control Loop with Fixed T
MIN
and T
RANGE
Values
TEMPERATURE (C)
T
MIN
01628 60
1
2
3
40
T
RANGE
= 40C
47
66
PWM DUTY CYCLE (%)
The fan will actually reach full-speed at a much lower
temperature, 28C. Case 3 shows that when the minimum
PWM duty cycle was increased to 73%, the temperature at
which the fan ran full-speed was 16C. So the effect of
increasing the minimum PWM duty cycle, with a fixed T
MIN
and fixed T
RANGE
, is that the fan will actually reach
full-speed (T
MAX
) at a lower temperature than
T
MIN
+T
RANGE
. How can T
MAX
be calculated?
In Automatic Fan Speed Control Mode, the register that
holds the minimum PWM duty cycle at T
MIN
, is the Fan
Speed Config Register (Register 0x22). Table 11 shows the
relationship between the decimal values written to the Fan
Speed Config Register and PWM duty cycle obtained.
Table 11. PROGRAMMING PWM DUTY CYCLE
Decimal Value PWM Duty Cycle
00 0%
01 7%
02 14%
03 20%
04 27%
05 33% (Default)
06 40%
07 47%
08 53%
09 60%
10 (0x0A) 67%
11 (0x0B) 73%
12 (0x0C) 80%
13 (0x0D) 87%
14 (0x0E) 93%
15 (0x0F) 100%
The temperature at which the fan will run full-speed
(100% duty cycle) is given by:
(eq. 2)
T
MAX
+ T
MIN
) ((Max DC * Min DC) T
RAN
G
E
ń10)
where:
T
MAX
= Temperature at which fan runs full speed
T
MIN
= Temperature at which fan will turn on
Max DC = Maximum Duty Cycle (100%) = 15 decimal
Min DC = Duty Cycle at T
MIN
, programmed into
Fan Speed Config Register
(default = 33% = 5 decimal)
T
RANGE
= PWM Duty Cycle versus Temperature Slope
Example 1
T
MIN
= 0C, T
RANGE
= 40C
Min DC = 53% = 8 decimal (Table 11)
Calculate T
MAX
(eq. 3)
T
MAX
+ T
MIN
) ((Max DC * Min DC) T
RANGE
ń10)
T
MAX
+ 0 ) ((100% DC * 53% DC) 40ń10)
T
MAX
+ 0 ) ((15 * 8) 4) + 28
T
MAX
=285C. (As seen on Slope 2 of Figure 26)
Example 2
T
MIN
= 0C, T
RANGE
= 40C
Min DC = 73% = 11 decimal (Table 11)
Calculate T
MAX
(eq. 4)
T
MAX
+ T
MIN
) ((Max DC * Min DC) T
RANGE
ń10)
T
MAX
+ 0 ) ((100% DC * 73% DC) 40ń10)
T
MAX
+ 0 ) ((15 * 11) 4) + 16
T
MAX
=165C. (As seen on Slope 3 of Figure 26)
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ADM1030ARQZ

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Manufacturer:
ON Semiconductor
Description:
Motor / Motion / Ignition Controllers & Drivers TDM & PWM FAN CNTRLRS IC
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