ADM1031ARQ-REEL7 ON Semiconductor, ADM1031ARQ-REEL7 Datasheet - Page 19

• 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

Programming the Filtered Automatic Fan Speed
Control Loop
PWM Duty Cycle Select Mode
clearing Bit 7 of Configuration Register 1 (Register 0×00).
This allows the user to directly control PWM duty cycle for
each fan.
allows fan control by varying PWM duty cycle. Values of
duty cycle between 0% and 100% can be written to the fan
speed configuration register (0×22) to control the speed of
each fan. Table 10 shows the relationship between hex
values written to the fan speed configuration register and
PWM duty cycle obtained.
set the PWM duty cycle for Fan 2.
Table 10. PWM Duty Cycle Select Mode
The ADM1031 can operate under software control by
Clearing Bit 5 and Bit 6 of Configuration Register 1
Bits <3:0> set the PWM duty cycle for Fan 1; Bits <7:4>
10. Select automatic fan speed control mode by setting
1. Program a value for T
2. Program a value for the slope T
3. T
4. Program a value for fan spin−up time.
5. Program the desired automatic fan speed control
6. Program a ramp rate for the filtered mode.
7. Program the ADC sample rate in the fan filter
8. Set Bit 0 to enable fan filtered mode for Fan 1.
9. Set Bit 1 to enable the fan filtered mode for Fan 2.
Hex Value
mode behavior, that is, which temperature channel
controls the fan.
register.
Bit 7 of Configuration Register 1.
MAX
0C
0D
00
01
02
03
04
05
06
07
08
09
0A
0B
0E
0F
= T
MIN
+ T
RANGE
MIN
.
PWM Duty Cycle
.
100%
14%
20%
27%
33%
40%
47%
53%
60%
67%
73%
80%
87%
93%
RANGE
0%
7%
.
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19
RPM Feedback Mode
RPM feedback mode. This involves programming the
desired fan RPM value to the device to set fan speed. The
advantages include a very tightly maintained fan RPM over
the fan’s life, and virtually no acoustic pollution due to fan
speed variation.
meaning a wide variation in speed for a typical batch of
identical fan models. If it is required that all fans run at
exactly 5000 RPM, it can be necessary to specify fans with
a nominal fan speed of 6250 RPM. However, many of these
fans run too fast and make excess noise. A fan with nominal
speed of 6250 RPM could run as fast as 7000 RPM at 100%
PWM duty cycle. RPM mode allows all of these fans to be
programmed to run at the desired RPM value.
0×00) to 0 places the ADM1031 under software control.
Once under software control, the device can be placed into
RPM feedback mode by writing to Bit 5 and Bit 6 of
Configuration Register 1. Writing a 1 to Bit 5 and Bit 6
selects RPM feedback mode for each fan.
fan RPM can be written to the fan tach high limit registers
(0×10, 0×11). The RPM feedback mode function allows a fan
RPM value to be programmed into the device, and the
ADM1031 maintains the selected RPM value by monitoring
the fan tach and speeding up the fan as necessary, should the
fan start to slow down. Conversely, should the fan start to
speed up due to aging, the RPM feedback slows the fan down
to maintain the correct RPM speed. The value to be
programmed into each fan tach high limit register is given by:
fan speed measured can be before generating an interrupt.
The slowest fan speed is measured when the count value
reaches 255.
Programming RPM Values in RPM Feedback Mode
register, an 8−bit count value is programmed instead. The
count to be programmed is given by:
The second method of fan speed control under software is
Fans typically have manufacturing tolerances of ±20%,
Clearing Bit 7 of Configuration Register 1 (Register
Once RPM feedback mode has been selected, the required
Count = (f × 60)/R × N
The speed range, N, really determines what the slowest
Since N = 2
Rather than writing a value such as 5000 to a 16−bit
Count = (f × 60)/R × N
where:
Count = (f × 60)/R × N
R = (f × 60)/Count × N
R = (11250 × 60)/255 × 2
R = (675000)/510
R = 1324 RPM, fan fail detect speed
where:
f = 11.25 kHz
R = desired RPM value
N = speed range; must be set to 2
f = 11.25 kHz
R = desired RPM value
N = speed range 2