EVAL-ADT7467EB Analog Devices Inc, EVAL-ADT7467EB Datasheet - Page 43

• Manufacturer Part Number: EVAL-ADT7467EB
• Description: BOARD EVALUATION FOR ADT7467
• Manufacturer: Analog Devices Inc
• Series: dBCool®r

Specifications of EVAL-ADT7467EB

• Sensor Type: Temperature
• Sensing Range: -40°C ~ 120°C
• Interface: SMBus (2-Wire/I²C)
• Sensitivity: ±1.5°C
• Voltage - Supply: 3 V ~ 5.5 V
• Embedded: No
• Utilized Ic / Part: ADT7467
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

STEP 4: PWM
PWM
the system runs. It is also the start speed for each fan in
automatic fan control mode when the temperature rises above
T
as low as possible. Depending on the fan used, the PWM
setting is usually in the 20% to 33% duty cycle range. This value
can be found through fan validation.
More than one PWM output can be controlled from a single
temperature measurement channel. For example, Remote 1
temperature can control PWM1 and PWM2 outputs. If two fans
are used on PWM1 and PWM2, each fan’s characteristics can be
set up differently. As a result, Fan 1 driven by PWM1 can have a
different PWM
PWM2. In Figure 59, PWM1
minimum duty cycle of 20%, and PWM2
at a minimum of 40% duty cycle; however, both fans turn on at
the same temperature, defined by T
MIN
Figure 59. Operating Two Fans from a Single Temperature Channel
. For maximum system acoustic benefit, PWM
MIN
PWM2
PWM1
PWM
Figure 58. PWM
is the minimum PWM duty cycle at which each fan in
100%
100%
MIN
0%
MIN
MIN
0%
MIN
MIN
value than that of Fan 2 connected to
FOR PWM (FAN) OUTPUTS
MIN
T
T
MIN
MIN
Determines Minimum PWM Duty Cycle
MIN
(front fan) is turned on at a
MIN
TEMPERATURE
TEMPERATURE
.
MIN
(rear fan) turns on
MIN
should be
MIN
Rev. A| Page 43 of 80
Programming the PWM
The PWM
minimum PWM duty cycle for each output to be configured
from 0% to 100%. This allows the minimum PWM duty cycle to
be set in steps of 0.39%.
The value to be programmed into the PWM
Example 1: For a minimum PWM duty cycle of 50%,
Example 2: For a minimum PWM duty cycle of 33%,
PWM
Reg. 0x64, PWM1 minimum duty cycle = 0x80 (50% default)
Reg. 0x65 PWM2 minimum duty cycle = 0x80 (50% default)
Reg. 0x66, PWM3 minimum duty cycle = 0x80 (50% default)
Fan Speed and PWM Duty Cycle
The PWM duty cycle does not directly correlate to fan speed in
RPM. Running a fan at 33% PWM duty cycle does not equate to
running the fan at 33% speed. Driving a fan at 33% PWM duty
cycle runs the fan at closer to 50% of its full speed, because fan
speed as a percentage of RPM generally relates to the square
root of the PWM duty cycle. Given a PWM square wave as the
drive signal, fan speed in RPM approximates to
STEP 5: PWM
PWM
system runs at during the automatic fan speed control loop.
For maximum system acoustic benefit, PWM
low as possible but capable of keeping the processor below its
maximum temperature limit, even in a worst case scenario. If
the THERM temperature limit is exceeded, the fans are still
boosted to 100% for fail-safe cooling.
There is a PWM
of this register is 0xFF and, therefore, has no effect unless it is
programmed.
Value (decimal) = PWM
Value (decimal) = 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 80 (hex)
Value (decimal) = 33/0.39 = 85 (decimal)
Value = 85 (decimal)l or 54 (hex)
%
MIN
MAX
fanspeed
Registers
is the maximum duty cycle that each fan in the
MIN
registers are 8-bit registers that allow the
MAX
MAX
=
limit for each fan channel. The default value
PWM
FOR PWM (FAN) OUTPUTS
MIN
duty
MIN
Registers
/0.39
cycle
×
10
MIN
MAX
register is given by
should be as
ADT7467