AN2586 Freescale Semiconductor / Motorola, AN2586 Datasheet - Page 2

• Manufacturer Part Number: AN2586
• Description: MPC8260 PowerQUICC II Family Power Distribution Trends
• Manufacturer: Freescale Semiconductor / Motorola

Introduction
Introduction
1 Introduction
One important step for designing a high speed digital system is to pre-plan for the power distribution
strategy. The strategy should cover the following aspects:
In the first item, designers should plan for an efficient supply that is capable of providing the following:
This document does not discuss power supply circuit design. The main assumption is that the supply circuit
is a nearly ideal DC source. This assumption simplifies the analysis by de-correlating supply circuit
dynamics from the network dynamics. Instead, this document’s main focus is the supply delivery network
and use of capacitors to bypass the supply network. When the supply circuit is planned, designers must plan
for placement of this circuit relative to the loads. In general it is always preferable to have the supply circuit
closer to the load. When that is difficult, a power delivery circuit is needed to reach far loads. The study of
delivery network characteristics as well as its interaction with the processor load, for instance, is vital to
understand and to design a minimum noise delivery system. To see the whole picture of our power network,
we must include most of the parasitics in the power distribution network as well as in the load chip packages.
In addition, we should include all the bypass caps in the model. Figure 1 shows conceptually the power
circuit of a single-chip load.
2 Statement of the Problem
From the perspective of the decoupling capacitor, the problem is that the following are not known:
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Power supply circuit
Power supply circuit design
Power supply delivery network
IC decoupling networks
Noise and EMI issues
Accurate output voltage levels at different loads
Protection to the load from the main conducted emissions and surges
Protection to the load from shorts and surges
Stability under various overall supply network, i.e., no oscillations, minimum drift, and so on
Enough bypass circuit for sudden demand from the load
Capability to sense loads when the loads are remote from the supply
Isolation of the main from the load
Fast dynamic response to load changes to stay within limit of the specified output levels
Bypass capacitors count
Bypass capacitors type
Bypass capacitors location
Bypass capacitors orientation
MPC8260 PowerQUICC II Family Power Distribution Trends: A Survey
Freescale Semiconductor, Inc.
For More Information On This Product,
Power delivery
Go to: www.freescale.com
Figure 1. Power Circuit
network
Bypass
network
MPC8260
MOTOROLA