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Intel® i960® RM/RN I/O Processor
Processor Power Supply Decoupling
10.0
Processor Power Supply Decoupling
Processor power supply decoupling is critical for reliable operation. With the 3.3 V ready system,
two areas of concern are described in
•
High frequency decoupling, necessitated by the processor's high speed operation
•
Low frequency decoupling, necessitated by the processor's power saving features
10.1
High Frequency Decoupling
Decoupling capacitors reduce voltage spikes by supplying extra current needed during switching.
Decoupling is especially critical on the
operation.
A reliable design will include a minimum of thirty-two 0.1 µF surface mount ceramic chip
capacitors between power and ground, evenly distributed, around the processor. The capacitors
must be placed as close to the processor as possible, attached directly to the power and ground
planes, otherwise circuit board inductance will significantly reduce their effectiveness.
Figure 10-23
the motherboard or add-in card. The BGA package in
normally it is not be visible from the back side. The outline around the BGA package is the 3.3 V
power island which is only needed on mixed voltage designs. When the design does not permit
components on the back side of the PCB, place the decoupling capacitors around the perimeter on
the component side of the PCB.
Inadequate high frequency decoupling results in unreliable or inconsistent program behavior.
These failures are often intermittent, and are difficult to diagnose and debug.
40
Section 10.1
is an example of how to place high frequency capacitors on the back (solder) side of
and
Section
10.2:
RM/RN I/O processor
because of its 100 MHz internal
Figure 10-23
*
is shown for reference only;
Design Guide
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