ADM1031ARQ-REEL7 ON Semiconductor, ADM1031ARQ-REEL7 Datasheet - Page 16

• 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

Register 0y24 Local Temperature T
<7:3> Local Temperature T
temperature at which the fan turns on when under auto fan
speed control. T
<2:0> Local Temperature T
temperature range over which automatic fan speed control
takes place.
Register 0y25, 0y26 Remote 1, 2 Temperature
T
<7:3> Remote Temperature T
which the fan switches on based on Remote X Temperature
Readings.
<2:0> Remote Temperature T
temperature range over which the fan is controlled based on
remote temperature readings.
MIN
00000 = 0°C
00001 = 4°C
00010 = 8°C
00011 = 12°C
01000 = 32°C (Default)
11110 = 120°C
11111 = 124°C
000 = 5°C
001 = 10°C
010 = 20°C
011 = 40°C
100 = 80°C
00000 = 0°C
00001 = 4°C
00010 = 8°C
00011 = 12°C
01100 = 48°C
11110 = 120°C
11111 = 124°C
000 = 5°C
001 = 10°C
010 = 20°C
011 = 40°C
100 = 80°C
/T
RANGE
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MIN
can be programmed in 4°C increments.
RANGE
MIN
RANGE
MIN
. Sets the temperature at
. These bits set the
. This nibble sets the
MIN
. This nibble sets the
/T
RANGE
http://onsemi.com
16
Filtered Control Mode
instantaneously to changes in temperature, that is, the PWM
duty cycle responds immediately to temperature change. In
certain circumstances, we do not want the PWM output to
react instantaneously to temperature changes. If significant
variations in temperature are found in a system, the fan
speed changes, which could be obvious to someone in close
proximity. One way to improve the system’s acoustics
would be to slow down the loop so that the fan ramps slowly
to its newly calculated fan speed. This also ensures that
temperature transients are effectively ignored, and the fan’s
operation is smooth.
automatic fan speed control loop. The first method is to ramp
the fan speed at a predetermined rate, to its newly calculated
value instead of jumping directly to the new fan speed. The
second approach involves changing the on−chip ADC
sample rate, to change the number of temperature readings
taken per second.
Bit 0 of the fan filter register (Register 0×23) for Fan 1 and
Bit 1 for Fan 2. Once the fan filter register has been written
to, and all other control loop parameters (such as T
T
into automatic fan speed control mode by setting Bit 7 of
Configuration Register 1 (Register 0×00) to 1.
Effect of Ramp Rate on Filtered Mode
in filtered mode. The PWM_OUT signal driving the fan has
a period, T, given by the PWM_OUT drive frequency, f,
since T = 1/f. For a given PWM period, T, the PWM period
is subdivided in to 240 equal time slots. One time slot
corresponds to the smallest possible increment in PWM duty
cycle. A PWM signal of 33% duty cycle is thus high for 1/3
× 240 time slots and low for 2/3 × 240 time slots. Therefore,
33% PWM duty cycle corresponds to a signal that is high for
80 time slots and low for 160 time slots.
2, 4, and 8. The ramp rates are actually discrete time slots.
For example, if the ramp rate = 8, then eight time slots are
added to the PWM_OUT high duty cycle each time the
PWM_OUT duty cycle needs to be increased. Figure 28
shows how the filtered mode algorithm operates.
RANGE
The
There are two means by which to apply filtering to the
The filtered mode on the ADM1031 is invoked by setting
Bits <6:5> of the fan filter register determine the ramp rate
The ramp rates in filtered mode are selectable between 1,
PWM_OUT
33% DUTY
CYCLE
Figure 27. 33% PWM Duty Cycle Presented
) have been programmed, the device can be placed
automatic
80 TIME
SLOTS
fan
in Time Slots
240 TIME SLOTS
(ONE PERIOD =
PWM OUTPUT
speed
160 TIME
SLOTS
control
loop
reacts
MIN
,