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ADM1030ARQ View Datasheet(PDF) - Analog Devices

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ADM1030ARQ Datasheet PDF : 28 Pages
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ADM1030
It should be noted however, that changing the minimum PWM
duty cycle affects the control loop behavior.
Slope 1 of Figure 10 shows TMIN set to 0C and the TRANGE
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
TMIN 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%.
100
93
87
80
73
66
60
53
47
40
33
0
16
28
40
60
TMIN
TEMPERATURE – ؇C
Figure 10. Effect of Changing Minimum Duty Cycle on
Control Loop with Fixed TMIN and TRANGE Values
The fan will actually reach full-speed at a much lower tempera-
ture, 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 mini-
mum PWM duty cycle, with a fixed TMIN and fixed TRANGE, is
that the fan will actually reach 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
Config Register (Register 0x22). Table VII shows the relation-
ship between the decimal values written to the Fan Speed Config
Register and PWM duty cycle obtained.
Table VII. Programming PWM Duty Cycle
Decimal Value
00
01
02
03
04
05
06
07
08
09
10 (0x0A)
11 (0x0B)
12 (0x0C)
13 (0x0D)
14 (0x0E)
15 (0x0F)
PWM Duty Cycle
0%
7%
14%
20%
27%
33% (Default)
40%
47%
53%
60%
67%
73%
80%
87%
93%
100%
The temperature at which the fan will run full-speed (100%
duty cycle) is given by:
TMAX = TMIN + ((Max DC Min DC) ¥ TRANGE/10)
where,
TMAX = Temperature at which fan runs full-speed.
TMIN = Temperature at which fan will turn on.
Max DC = Maximum Duty Cycle (100%) = 15 decimal.
Min DC = Duty Cycle at TMIN, programmed into Fan Speed
Config Register (default = 33% = 5 decimal).
TRANGE = PWM Duty Cycle versus Temperature Slope.
Example 1
TMIN
= 0C, TRANGE = 40C
Min DC = 53% = 8 decimal (Table VII)
Calculate TMAX.
TMAX = TMIN + ((Max DC – Min DC) ¥ TRANGE/10)
TMAX = 0 + ((100% DC – 53% DC) ¥ 40/10)
TMAX = 0 + ((15 – 8) ¥ 4) = 28
TMAX = 28؇C (As seen on Slope 2 of Figure 10)
Example 2
TMIN
= 0C, TRANGE = 40C
Min DC = 73% = 11 Decimal (Table VII)
Calculate TMAX.
TMAX = TMIN + ((Max DC – Min DC) ¥ TRANGE/10)
TMAX = 0 + ((100% DC – 73% DC) ¥ 40/10)
TMAX = 0 + ((15 – 11) ¥ 4) = 16
TMAX = 16؇C (As seen on Slope 3 of Figure 10)
Example 3
TMIN
= 0C, TRANGE = 40C
Min DC = 33% = 5 Decimal (Table VII)
Calculate TMAX.
TMAX = TMIN + ((Max DC – Min DC) ¥ TRANGE/10)
TMAX = 0 + ((100% DC – 33% DC) ¥ 40/10)
TMAX = 0 + ((15 – 5) ¥ 4) = 40
TMAX = 40؇C (As seen on Slope 1 of Figure 10)
In this case, since the Minimum Duty Cycle is the default 33%,
the equation for TMAX reduces to:
TMAX = TMIN + ((Max DC – Min DC) ¥ TRANGE/10)
TMAX = TMIN + ((15 – 5) ¥ TRANGE/10)
TMAX
= TMIN + (10 ¥ TRANGE/10)
TMAX
= TMIN + TRANGE
–14–
REV. A
 

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