Datasheet 15
Electrical Specifications
2Electrical Specifications
This chapter describes the electrical characteristics of the processor interfaces and signals. DC
electrical characteristics are provided.

2.1 Power and Ground Lands

The Intel® Pentium® D processor has 226 VCC (power) and 273 VSS (ground) inputs for on-chip
power distribution. All VCC lands must be connected to the processor power plane, while all VSS
lands must be connected to the system ground plane. The processor VCC lands must be supplied
with the voltage determined by the processor Voltage IDentification (VID) lands.
The Pentium D processor has 24 signals that are denoted as VTT that provide termination for the
front side bus and power to the I/O buffers. A separate supply must be implemented for these lands,
that meets the VTT specifications outlined in Table 2 -3.

2.2 Decoupling Guidelines

Due to its large number of transistors and high internal clock speeds, the processor is capable of
generating large current swings between low and full power states. This may cause voltages on
power planes to sag below their minimum values if bulk decoupling is not adequate. Larger bulk
storage (CBULK), such as electrolytic or aluminum-polymer capacitors, supply current during
longer lasting changes in current demand by the component, such as coming out of an idle
condition. Similarly, they act as a storage well for current when entering an idle condition from a
running condition. The motherboard must be designed to ensure that the voltage provided to the
processor remains within the specifications listed in Tabl e 2-3. Failure to do so can result in timing
violations or reduced lifetime of the component. For further information and design guidelines,
refer to the Voltage Regulator Down (VRD) 10.1 Design Guide For Desktop LGA775 Socket.

2.2.1 VCC Decoupling

VCC regulator solutions need to provide sufficient decoupling capacitance to satisfy the processor
voltage specifications. This includes bulk capacitance with low effective series resistance (ESR) to
keep the voltage rail within specifications during large swings in load current. In addition, ceramic
decoupling capacitors are required to filter high frequency content generated by the front side bus
and processor activity. Consult the Voltage Regulator Down (VRD) 10.1 Design Guide For
Desktop LGA775 Socket for further information.

2.2.2 VTT Decoupling

Decoupling must be provided on the motherboard. Decoupling solutions must be sized to meet the
expected load. To insure compliance with the specifications, various factors associated with the
power delivery solution must be considered including regulator type, power plane and trace sizing,
and component placement. A conservative decoupling solution would consist of a combination of
low ESR bulk capacitors and high frequency ceramic capacitors.