AN2127 Freescale Semiconductor / Motorola, AN2127 Datasheet - Page 11

• Manufacturer Part Number: AN2127
• Description: EMC Guidelines for MPC Based Automotive Powertrain Systems
• Manufacturer: Freescale Semiconductor / Motorola

Freescale Semiconductor, Inc.
Digital
Analog
I/O
0 V
Power Supply
Battery
Figure 6 Typical MCU Application Grounding Example
3.3 Micro-Island Approach to Decoupling and Grounding
The micro-island approach to decoupling and grounding is the premier solution for high-speed digital
noise isolation, and as such it tends to cost more to implement than standard decoupling and grounding.
The micro-island technique aggressively seeks to isolate all high-speed digital noise to a micro-island
instead of allowing it to propagate throughout the entire system. All high-speed digital components such
as the MCU, crystal, and memory are grouped together in an isolated island and a moat surrounds the
entire island. There are isolated power and ground islands which are also surrounded by moats; the
ground island extends out further than the power island. Power entry to the micro-island is filtered using
a three terminal EMI chip capacitor or a
-filter consisting of a low-Q inductor or ferrite bead in combi-
nation with some capacitors. The micro-island is decoupled with 22 of the 0306-style 10 nF decoupling
capacitors which are evenly distributed throughout the micro-island area. Any signal line leaving the mi-
cro-island area is filtered using resistors or ferrites.
Figure 7
contains additional details.
EMC Guidelines for MPC500-Based Automotive Powertrain Systems
MOTOROLA
Rev. 0, 15 July 2001
11
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