ADM1031ARQ-REEL7 ON Semiconductor, ADM1031ARQ-REEL7 Datasheet - Page 17

• 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

cycle based on the temperature measured. If the new PWM
duty cycle value is greater than the previous PWM value, the
previous PWM duty cycle value is incremented by either 1,
2, 4, or 8 time slots (depending on the setting of bits <6:5>
of the fan filter register). If the new PWM duty cycle value
is less than the previous PWM value, the previous PWM
duty cycle is decremented by 1, 2, 4, or 8 time slots. Each
time the PWM duty cycle is incremented or decremented, it
is stored as the previous PWM duty cycle for the next
comparison.
What does an increase of 1, 2, 4, or 8 time slots
actually mean in terms of PWM duty cycle?
1/240 of the PWM period. In filtered auto fan speed control
mode, incrementing or decrementing by 1 changes the PWM
output duty cycle by 0.416%.
increases or decreases the PWM duty cycle by the amounts
shown in Table 8, depending on whether the temperature is
increasing or decreasing.
PWM duty cycle for filtered mode. The ADC sample rate is
the highest sample rate; 11.25 kHz. The ramp rate is set to
8, which would correspond to the fastest ramp rate. With
these settings, it took approximately 12 seconds to go from
0% duty cycle to 100% duty cycle (full−speed). The T
value = 32°C and the T
temperature increased very rapidly, the fan gradually ramps
up to full speed.
Table 8. Effect of Ramp Rates on PWM_OUT
The filtered mode algorithm calculates a new PWM duty
A ramp rate of 1 corresponds to one time slot, which is
So programming a ramp rate of 1, 2, 4, or 8 simply
Figure 29 shows remote temperature plotted against
Ramp Rate
1
2
4
8
Figure 28. Filtered Mode Algorithm
VALUE BY RAMP
PREVIOUS PWM
TEMPERATURE
PWM VALUE >
DUTY CYCLE
CALCULATE
INCREMENT
PREVIOUS
NEW PWM
VALUE?
IS NEW
READ
RATE
RANGE
YES
PWM Duty Cycle Change
= 80°C. Even though the
NO
0.416%
0.833%
1.66%
3.33%
DECREMENT
PWM VALUE
PREVIOUS
BY RAMP
RATE
http://onsemi.com
MIN
17
affects the control loop. The overall response of the fan is
slower. Because the ramp rate is reduced, it takes longer for
the fan to achieve full running speed. In this case, it took
approximately 22 seconds for the fan to reach full speed.
of 2. In this instance the fan took about 54 seconds to reach
full running speed.
Figure 30 shows how changing the ramp rate from 8 to 4
Figure 31 shows the PWM output response for a ramp rate
120
110
140
120
100
140
120
100
80
60
40
20
80
60
40
20
80
60
40
20
0
0
0
Figure 29. Filtered Mode with Ramp Rate = 8
Figure 30. Filtered Mode with Ramp Rate = 4
Figure 31. Filtered Mode with Ramp Rate = 2
0
0
0
R
R
R
TEMP
TEMP
TEMP
PWM DUTY CYCLE
PWM DUTY CYCLE
TIME (s)
TIME (s)
TIME (s)
PWM DUTY CYCLE
54
22
12
140
120
100
80
60
40
20
0
120
100
80
60
40
20
0
120
100
80
60
40
20
0