Intel® Xeon™ Processor with 800 MHz System Bus
90 Datasheet
A new 4-pin PWM/T-diode controlled active fan heatsink solution will replace the 3-pin thermistor
controlled solution after initial boxed Intel® Xeon™ processor with 800 MHz system bus
introduction. This new solution is being offered to help provide better control over pedestal chassis
acoustics. This is achieved though more accurate measurement of processor die temperature
through the processor’s temperature diode (T-diode). Fan RPM is modulated through the use of an
ASIC located on the baseboard, that sends out a PWM control signal to the 4th pin of the connector
labeled as Control. This heatsink solution also requires a constant +12 V supplied to pin 2 and
does not support variable voltage control or 3-pin PWM control. See Table 30 for details on the 3-
and 4-pin active heatsink solution connectors.
If the new 4-pin active fan heatsink solution is connected to an older 3-pin baseboard CPU fan
header it will default back to a thermistor controlled mode, allowing compatibility with existing
designs. It may be necessary to change existing baseboard designs to support this new 4-pin active
heatsink solution if PWM/T-diode control is desired. It may also be necessary to verify that the
larger 4-pin fan connector will not interfere with other components installed on the baseboard.
The fan power header on the baseboard must be positioned to allow the fan heatsink power cable to
reach it. The fan power header identification and location must be documented in the suppliers
platform documentation, or on the baseboard itself. The baseboard fan power header should be
positioned within 177.8 mm [7 in.] from the center of the processor socket.
Table 29. PWM Fan Frequency Specifications (4-pin active CEK heatsink)
Description Min Frequency Nominal Frequency Max Frequency Unit
PWM Control
Frequency Range
21,000 25,000 28,000 Hz
Table 30. Fan Specifications (3- and 4-pin active CEK heatsink)
Description Min
Typ
Steady
Max
Steady
Max
Startup
Unit
+12 V: 12 volt fan power supply 10.8 12 12 13.2 V
IC: Fan Current Draw N/A 1 1.25 1.5 A
SENSE: SENSE frequency 2 2 2 2 Pulses per fan
revolution
Figure 27. Fan Cable Connector Pinout (3-pin active CEK heatsink)
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