Intel Xeon Processor Multiprocessor Platform Design Guide

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Processor Power Distribution Guidelines
8.7 Voltage Regulator
Intel recommends that the processor power provided by a voltage regulator module (one per
processor) meets the specifications as described by the VRM 9.1 DC-DC Converter Design
Guidelines. The voltage regulator definition includes Remote-Sense, Current Share and Output
Enable features. Voltage regulator designers must provide these features as well as meeting voltage
and current requirements set forth in the regulator design guidelines. The voltage regulator output
slew rate is generally less than 50 A/µs. The slew rate at the processor socket pins can be as high as
450 A/µs. The system designer needs to provide adequate bulk and high-frequency decoupling on
the baseboard to meet the processor required slew rate. Generally, the main power source for the
voltage regulator is 12 V +5%, -8%. This voltage is supplied by a conventional computer power
supply through a cable to the baseboard.
8.7.1 Voltage Regulator Design
It is outside the scope of this document to provide all the nuances involved in creating a high
performance voltage regulator. Intel provides a list of enabled VRM suppliers. Also, manufacturers
of voltage regulator IC controllers provide application notes, demo modules, design reviews and
other forms of customer support including on site design assistance.
8.7.2 Voltage Regulator System Matching
8.7.2.1 Voltage Regulator Output
Some voltage regulator modules may be purchased with output capacitance included although
many voltage regulator modules available today rely entirely on the baseboard for their output
filtering capacitance. Regardless, the transient response or bandwidth of the voltage regulator must
complement the combined output decoupling and storage capacitors so that the DC to 10 MHz
impedance seen by the processor socket is less than 0.25 mΩ for a four processor system.
8.7.2.2 Voltage Regulator Input
Some voltage regulator modules may be purchased with input power filtering included although
many voltage regulator modules available today rely entirely on the baseboard for their input
power filtering. Input filtering requirements are dependant upon the power source and transient
tolerance of common loads. However, for a typical 12 V power source, the voltage regulator input
filter must limit its power source's current rate of change to less than 100 mA/µs. Other peripheral
12 V components should be powered separately from the voltage regulators.
8.7.2.3 Voltage Regulator Cooling
High performance voltage regulators generally operate at less than 85% efficiency. Careful
attention must be given to providing adequate cooling air or thermal conduction paths. If using
voltage regulator modules, the temperature of the module board must not exceed 90 °C at the
connector interface. Specifically, to maintain the connector within its operating temperature range,
the VRM board must not exceed 90 °C at any point within 2.54 mm of the top of the connector.