AN2127 Freescale Semiconductor / Motorola, AN2127 Datasheet

AN2127

Manufacturer Part Number

AN2127

Description

EMC Guidelines for MPC Based Automotive Powertrain Systems

Manufacturer

Freescale Semiconductor / Motorola

Datasheet

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This document contains information on a new product. Specifications and

information herein are subject to change without notice.

EMC Guidelines for MPC500-Based Automotive

Powertrain Systems

by Stevan Dobrasevic

Advanced Vehicle Systems Division, Motorola SPS

Rev. 1, 11 March 2002

1 Introduction

2 Software Guidelines

2.1 CLKOUT

MOTOROLA

SEMICONDUCTOR

APPLICATION NOTE

An increasingly important consideration in the design of automotive powertrain systems is electromag-

netic compatibility (EMC). EMC consists of four sub-groups: radiated emissions, conducted emissions,

radiated susceptibility, and conducted susceptibility. This application note focuses on guidelines for re-

ducing radiated emissions from MPC500-based powertrain systems. These guidelines are not a com-

plete set of all known EMC techniques, instead they are some specific recommendations for MPC500-

based systems. This application note should be used in conjunction with other more general sources of

EMC guidelines, many such sources are suggested in the

The reduction of radiated emissions from automotive modules is an effort to reduce the likelihood of

electromagnetically interfering with the automobile’s other electronic systems, such as its radio receiver.

Electromagnetic interference (EMI) involves the coupling of a noise source to a victim receiver. For this

discussion, the noise source is the automotive module and within the module the MCU can be a source

of electrical noise.

Since the MPC500 family is packaged in a 27-mm x 27-mm PBGA and the maximum frequency of in-

terest is 1000 MHz, the MCU itself is not a very efficient radiator. However, the MCU can couple noise

onto the printed circuit board (PCB), and the PCB and attached cabling can be efficient radiators. There-

fore, the goal is to reduce the amount of noise the MCU generates and to reduce the coupling of the

MCU’s noise onto the PCB.

In general, experiments have shown that the MPC500 family have four primary sources of noise: CLK-

OUT, ENGCLK, core power supply, and the ADDR/DATA bus pins. Of these, CLKOUT is usually the

cause of any given EMI system problem and/or EMI module specification failure. Similarly, ENGCLK

can be a significant noise source if driven at system frequency. However, ENGCLK is normally used at

a much lower frequency and is therefore less of a concern. Simultaneous switching noise (SSN) due to

the switching of digital logic on MCUs causes noise on the core power supply (V

less of an issue than the other three noise sources discussed.

The CLKOUT driver has software selectable drive strengths which are controlled by the COM bits in the

SCCR register. CLKOUT is enabled after reset and the default value of drive strength is determined by

the BDRV bit in the hard reset configuration word. Many board applications are configured such that

for MPC56x). ADDR/DATA bus noise mainly increases the broad band emissions and is therefore

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

4 References

section.

Order this document by:

DDI

for MPC55x and

AN2127/D

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AN2127 Summary of contents

Page 1

... BDRV bit in the hard reset configuration word. Many board applications are configured such that This document contains information on a new product. Specifications and information herein are subject to change without notice. © MOTOROLA 2002, All Rights Reserved For More Information On This Product, 4 References Go to: www.freescale.com Order this document by: AN2127/D section. for MPC55x and DDI ...

Page 2

Freescale Semiconductor, Inc. this results in the selection of full drive strength. Full drive strength for CLKOUT assumes a load and is intended for test purposes only. Unless full drive strength is required for timing considerations, it ...

Page 3

Freescale Semiconductor, Inc. 2.6 Slew Rate Slew rate is controlled by the SLRC[0:3] bits in the PDMCR register. Slow slew rate should be used unless insufficient for system timing requirements. The default configuration is for slow slew rate. Slow slew ...

Page 4

Freescale Semiconductor, Inc. Trace Capacitor Incorrect Figure 1 Vias for Decoupling Capacitors The remaining capacitors are required for decoupling the low-voltage (3.3-V or 2.6-V) MCU supply. The MPC55x and the MPC56x have different ball maps. Also, some ...

Page 5

Freescale Semiconductor, Inc. Figure 2 MPC55x Double-Sided Component Placement Application 2. MPC55x Single-Sided Component Placement Application In this situation, the capacitors should be placed as close as possible, and on the same side of the PCB, as the MCU. Connect ...

Page 6

Freescale Semiconductor, Inc. land). The negative side of the capacitors should be connected with multiple vias to the ground plane (see Figure 3). Figure 3 MPC55x Single-Sided Component Placement Application 3. MPC56x Double-Sided Component Placement Application With this approach, the ...

Page 7

Freescale Semiconductor, Inc. balls should NOT be tied directly to the power plane, but instead should route up to the top layer and over to the 10 nF capacitors. After routing to the 10 nF capacitors, a connection to the ...

Page 8

Freescale Semiconductor, Inc. vias from VDD balls to top side (not connected to power plane) not shown in side view vias to power plane Figure 4 MPC56x Double-Sided Component Placement Application Example 4. MPC56x Single-Sided Component Placement Application In this ...

Page 9

Freescale Semiconductor, Inc. which connect all four V balls to the two capacitors. There should also be wide topside strips con- DD necting all four V balls to the capacitors. After the connected to the power and ...

Page 10

Freescale Semiconductor, Inc. via to ground plane via to power plane VDD capacitor VSS not shown in side view Figure 5 MPC56x Single-Sided Component Placement Application 3.2 Standard Grounding Most MCU based systems will partition different classes of circuits with ...

Page 11

Freescale Semiconductor, Inc 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 ...

Page 12

Freescale Semiconductor, Inc. Micro-Island Signals Leaving Micro-Island Resistors Figure 7 Typical Micro-Island Approach to Decoupling and Grounding 3.4 Signal Routing and Terminations High-speed signals should be isolated as much as possible by using spacing and shielding of the signal traces. ...

Page 13

Freescale Semiconductor, Inc. Components The use of many vias for power and ground connections is stressed throughout this document. Howev- er, care must be taken to avoid degradation of the power and ground planes by too many via anti-pads obstructing ...

Page 14

Freescale Semiconductor, Inc. Circuit EXTAL XTAL Figure 10 Oscillator CIrcuit and Layout 4 References 4.1 MPC500 Family Reference Documentation 1. MPC555 / MPC556 User’s Manual 2. MPC565 / MPC566 Reference Manual 3. MPC561/MPC563 Reference ...

Page 15

Freescale Semiconductor, Inc. 4.3 General EMC References 1. Clayton, Paul. Introduction to Electromagnetic Compatibility 2. Johnson, Howard. High-Speed Digital Design: A Handbook of Black Magic 1993. 3. Ott, Henry. Noise Reduction Techniques in Electronic Systems 4. Kimmel Gerke Associates website, ...

Page 16

... For More Information On This Product, JAPAN Motorola Japan Ltd. SPS, Technical Information Center 3-20-1, Minami-Azabu, Minato-ku Tokyo 106-8573 Japan 81-3-3440-3569 ASIA/PACIFIC Motorola Semiconductors H.K. Ltd. Silicon Harbour Centre 2 Dai King Street Tai Po Industrial Estate Tai Po, N.T., Hong Kong 852-26668334 Go to: www.freescale.com Home Page http://www.motorola.com/semiconductors Order Number AN2127/D ...

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