Electrical Specifications
2
Electrical 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 Pentium 4 processor has 226 VCC (power), 24 VTT and 273 VSS (ground) inputs
for on-chip power distribution. All power lands must be connected to VCC, while all VSS
lands must be connected to a system ground plane. The processor VCC lands must be
supplied the voltage determined by the Voltage IDentification (VID) lands.
Twenty-four (24) signals 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 4.
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. This may cause voltages on power planes
to sag below their minimum specified 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 Table 4. Failure to do so can result in timing violations or reduced lifetime of
the component.
2.2.1
2.2.2
V
Decoupling
CC
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 and Transportable
LGA775 Socket for further information.
V Decoupling
TT
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.
Datasheet
13
INTEL [ INTEL ]
