ADM1031ARQZ View Datasheet(PDF) - ON Semiconductor
Part Name
Description
Manufacturer
ADM1031ARQZ Datasheet PDF : 30 Pages
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ADM1031
100
93
87
80
73
66
60
TRANGE = 5°C
53
TRANGE = 10°C
47
TRANGE = 20°C
TRANGE = 40°C
40
TRANGE = 80°C
33
0 5 10 20
TMIN
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 4°C.
100
93
87
80
73
66
60
53
47
40
33
0
TMIN
TRANGE = 40°C
20
40
60
80
TMAX = TMIN + TRANGE
TEMPERATURE (°C)
Figure 23. Effect of Increasing TMIN Value on
Control Loop
Fan Spin−Up
As mentioned in the How Does the Control Loop Work?
section, once the temperature being measured exceeds the
TMIN value programmed, the fan turns 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 can be reduced in line with the
temperature being measured.
The ADM1031 allows fan spin−up times between 200 ms
and 8 seconds. Bits <2:0> of Fan Characteristics Register 1
(Register 0×20) and Fan Characteristic Register 2 (Register
0×21) program the fan spin−up times.
Table 5. Fan Spin−Up Times
Bits 2:0
Spin−Up Time
(Fan Characteristics Registers 1, 2)
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 ADM1031 device can be
programmed. The ADM1031 is placed into automatic fan
speed control mode by setting Bit 7 of Configuration
Register 1 (Register 0×00). The device powers up in
automatic fan speed control mode by default. The control
mode offers further flexibility in that the user can decide
which temperature channel/channels control each fan.
Table 6. Auto Mode Fan Behavior
Bits 6, 5
00
01
10
11
Control Operation (Configuration Register 1)
Remote Temperature 1 Controls Fan 1
Remote Temperature 2 Controls Fan 2
Remote Temperature 1 Controls Fan 1 and 2
Remote Temperature 2 Controls Fan 1 and 2
Maximum Speed Calculated by Local and Remote
Temperature Channels Controls Fans 1 and 2
When Bit 5 and Bit 6 of Configuration Register 1 are both
set to 1, increased flexibility is offered. 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 fans.
Figure 24 and Figure 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 Bit 5 and
Bit 6 of Configuration Register 1 are set to 11. Figure 24
shows the control loop for the local temperature channel. Its
TMIN value has been programmed to 20°C, and its TRANGE
value is 40°C. The local temperature’s TMAX is thus 60°C.
Figure 25 shows the control loop for the remote temperature
channel. Its TMIN value has been set to 0°C, while its
TRANGE = 80°C. Therefore, the remote temperature’s TMAX
value is 80°C.
Consider if both temperature channels measure 40°C.
Both control loops calculate a PWM duty cycle of 66%.
Therefore, the fan is driven at 66% duty cycle. If both
temperature channels measure 20°C, the local channel
calculates 33% PWM duty cycle, while the Remote 1
channel calculates 50% PWM duty cycle. Thus, the fans are
driven at 50% PWM duty cycle. Consider the local
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