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Fan Performance for Reference Design
Appendix F Fan Performance for
The fan power requirements for proper operation are listed in Table 7–3.
Table 7–3. Fan Electrical Performance Requirements
Maximum Average fan current draw
Fan start-up current draw
Fan start-up current draw maximum
duration
Fan header voltage
Tachometer output
Tachometer output signal
PWM signal input frequency
PWM signal pull up in fan
PWM signal current source
PWM signal maximum voltage for logic
low
PWM compliant function
In addition to comply with overall thermal requirements (Sections 5.1.1 and 6.2), and
the general environmental reliability requirements (Sections 5.2 and 6.3) the fan
should meet the following performance requirements:
•
Mechanical wear out represents the highest risk reliability parameter for fans. The
capability of the functional mechanical elements (ball bearing, shaft, and tower
assembly) must be demonstrated to a minimum useful lifetime of 57,000 hours.
•
In addition to passing the environmental reliability tests described in Sections 5.2
and 6.3, the fan must demonstrate adequate performance after 7,500 on/off
cycles with each cycle specified as 3 minutes on, 2 minutes off, at a temperature
of 70 °C.
See the Fan Specification for 4-wire PWM Controlled Fans for additional details on the
fan specification.
Thermal and Mechanical Design Guidelines
Reference Design
Requirement
Value
1.5 A
2.2 A
1.0 second
12 V ± 5%
2 pulse per revolution
Open-collector (open-drain)
21 kHz to 28 kHz
3.3 V (recommended max)
5.25 V (absolute max)
Imax = 5 mA
(short circuit current)
VIL = 0.8 V
RPM must be within spec for specified
duty cycle
§
107
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