ADM1031ARQZ View Datasheet(PDF) - ON Semiconductor
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ADM1031ARQZ Datasheet PDF : 30 Pages
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ADM1031
speed. Bit 1 (Fan Fault) is set whenever a fan tach failure is
detected. Once cleared, it reasserts on subsequent fan tach
failures.
Bit 2 and Bit 3 of Status Register 1 and Status Register 2
are the Remote 1 and Remote 2 Temperature High and Low
status bits. Exceeding the high or low temperature limits for
the external channel sets these status bits. Reading the status
register clears these bits. However, these bits are reasserted
if the out−of−limit condition still exists on the next
monitoring cycle. Bit 6 and Bit 7 are the Local Temperature
High and Low status bits. These behave exactly the same as
the Remote Temperature High and Low status bits. Bit 4 of
Status Register 1 indicates that the Remote Temperature
THERM limit has been exceeded. This bit gets cleared on a
read of Status Register 1 (see Figure 20). Bit 5 indicates a
remote diode error. This bit is a 1 if a short or open is detected
on the remote temperature channel on powerup. If this bit is
set to 1 on powerup, it cannot be cleared. Bit 6 of Status
Register 2 (0×03) indicates that the Local THERM limit has
been exceeded. This bit is cleared on a read of Status
Register 2. Bit 7 indicates that THERM has been pulled low
as an input. This bit can also be cleared on a read of Status
Register 2.
THERM LIMIT
5°
TEMP
THERM
INT REARMED
INT
STATUS REG. READ
Figure 20. Operation of THERM and INT Signals
Figure 20 shows the interaction between INT and
THERM. Once a critical temperature THERM limit is
exceeded, both INT and THERM assert low. Reading the
status registers clears the interrupt and the INT pin goes
high. However, the THERM pin remains asserted until the
measured temperature falls 5°C below the exceeded
THERM limit. This feature can be used to CPU throttle or
drive a fan full speed for maximum cooling. Note that the
INT pin for that interrupt source is not rearmed until the
temperature has fallen below the THERM limit –5°C. This
prevents unnecessary interrupts from tying up valuable CPU
resources.
Fan Control Modes of Operation
The ADM1031 has four different modes of operation.
These modes determine the behavior of the system.
1. Automatic Fan Speed Control Mode.
2. Filtered Automatic Fan Speed Control Mode.
3. PWM Duty Cycle Select Mode (directly sets fan
speed under software control).
4. RPM Feedback Mode.
Automatic Fan Speed Control
The ADM1031 has a local temperature channel and two
remote temperature channels, which can be connected to an
on−chip diode−connected transistor on a CPU. These three
temperature channels can be used as the basis for an
automatic fan speed control loop to drive fans using pulse
width modulation (PWM).
How Does the Control Loop Work?
The automatic fan speed control loop is shown in Figure 21.
MAX
SPIN−UP FOR SECONDS
FAN
SPEED
MIN
TMIN
TMAX = TMIN + TRANGE
TEMPERATURE
Figure 21. Automatic Fan Speed Control Loop
TMIN is the temperature at which the fan should switch on
and run at minimum speed. The fan only turns on once the
temperature being measured rises above the TMIN value
programmed. The fan spins up for a predetermined time
(default = 2 seconds). See the Fan Spin−Up section for more
details.
TRANGE is the temperature range over which the
ADM1031 automatically adjusts the fan speed. As the
temperature increases beyond TMIN, the PWM_OUT duty
cycle increases accordingly. The TRANGE parameter
actually defines the fan speed vs. temperature slope of the
control loop.
TMAX is the temperature at which the fan is at its
maximum speed. At this temperature, the PWM duty cycle
driving the fan is 100%. TMAX is given by TMIN + TRANGE.
Since this parameter is the sum of the TMIN and TRANGE
parameters, it does not need to be programmed into a register
on−chip.
A hysteresis value of 5°C is included in the control loop
to prevent the fan continuously switching on and off if the
temperature is close to TMIN. The fan continues to run until
the temperature drops 5°C below TMIN.
Figure 22 shows the different control slopes determined
by the TRANGE value chosen, and programmed into the
ADM1031. TMIN is set to 0°C to start all slopes from the
same point. The figure shows how changing the TRANGE
value affects the PWM duty cycle vs. temperature slope.
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