ADM1031ARQ-REEL7 ON Semiconductor, ADM1031ARQ-REEL7 Datasheet - Page 18

• Manufacturer Part Number: ADM1031ARQ-REEL7
• Description: IC SENSOR 2-TEMP/FAN CTRL 16QSOP
• Manufacturer: ON Semiconductor

Specifications of ADM1031ARQ-REEL7

• Rohs Status: RoHS non-compliant
• Function: Fan Control, Temp Monitor
• Topology: ADC, Comparator, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: 0°C ~ 100°C, External Sensor
• Output Type: SMBus™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: 0°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP

temperature with the slowest ramp rate. The ramp rate is set
to 1, while all other control parameters remain the same.
With the slowest ramp rate selected, it took 112 seconds for
the fan to reach full speed.
at which the fan reacts to temperature change is dependent
on the ramp rate selected in the fan filter register. The higher
the ramp rate, the faster the fan reaches the newly calculated
fan speed.
temperature varies. As the temperature rises, the fan speed
ramps up. Small drops in temperature do not affect the
ramp−up function because the newly calculated fan speed is
still higher than the previous PWM value. The filtered mode
allows the PWM output to be made less sensitive to
temperature variations. This is dependent on the ramp rate
selected and the ADC sample rate programmed into the fan
filter register.
Effect of ADC Sample Rate on Filtered Mode
characteristics is to adjust the ADC sample rate. The faster
Figure 33. How Fan Reacts to Temperature Variation
Finally, Figure 32 shows how the control loop reacts to
As can be seen from Figure 29 through Figure 32, the rate
Figure 33 shows the behavior of the PWM output as
The second way to change the filtered mode
120
110
80
60
40
20
90
80
70
60
50
40
30
20
10
0
0
Figure 32. Filtered Mode with Ramp Rate = 1
0
in Filtered Mode
R
TEMP
TIME (s)
TIME (s)
R
TEMP
PWM DUTY CYCLE
PWM DUTY CYCLE
112
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140
120
100
80
60
40
20
0
90
80
70
60
50
40
30
20
10
0
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the ADC sample rate, the more temperature samples are
obtained per second. One way to apply filtering to the
control loop is to slow down the ADC sampling rate. This
means that the number of iterations of the filtered mode
algorithm per second is effectively reduced. If the number
of temperature measurements per second is reduced, how
often the PWM_OUT signal controlling the fan is updated
is also reduced.
ADC sample rate. The default ADC sample rate is 1.4 kHz.
The ADC sample rate is selectable from 87.5 Hz to 11.2 kHz.
Table 9 shows how many temperature samples are obtained
per second, for each of the ADC sample rates.
Relevant Registers for Filtered Automatic Fan Speed
Control Mode
automatic fan speed control mode, the following register
needs to be programmed.
Register 0y23 Fan Filter Register
<7> Spin−up Disable: When this bit is set to 1, fan spin−up
is disabled. (Default = 0)
<6:5> Ramp Rate: These bits set the ramp rate for filtered
mode.
<4:2> ADC Sample Rate.
<1> Fan 2 Filter Enable: When this bit is set to 1, it enables
filtering on Fan 2. Default = 0.
<0> Fan 1 Filter Enable: When this bit is set to 1, it enables
filtering on Fan 1. Default = 0.
Table 9. Temperature Updates per Second
Bits <4:2> of the fan filter register (Register 0×23) set the
In addition to the registers used to program the normal
ADC Sample Rate
00 = 1 (0.416% Duty Cycle Change)
01 = 2 (0.833% Duty Cycle Change)
10 = 4 (1.66% Duty Cycle Change)
11 = 8 (3.33% Duty Cycle Change)
000 = 87.5 Hz
001 = 175 Hz
010 = 350 Hz
011 = 700 Hz
100 = 1.4 kHz (Default)
101 = 2.8 kHz
110 = 5.6 kHz
111 = 11.2 kHz
11.2 kHz
700 kHz
87.5 Hz
1.4 kHz
2.8 kHz
5.6 kHz
175 Hz
350 Hz
Temperature Updates/Sec
1 (Default)
0.0625
0.125
0.25
0.5
2
4
8