720 EMC PIC® 单片机的EMC兼容性设计.

720 EMC PIC® 单片机的EMC兼容性设计

议程 EMC介绍条例元器件选择线路端接处理 PCB 布线微控制器电路软件参考资料

Microchip Technology Inc. MASTERs 2003
EMC介绍 EMC - 电磁兼容性一个电子系统与其它电子系统兼容而不产生干扰或受到影响的能力一个电子系统如果符合以下条件就是电磁兼容: 不会导致对其它系统的干扰不会受其它系统的电磁干扰不会对自己产生干扰 Designing products for EMC are not only important to the operation of the device in its intended environment, but also to meet regulations in the various countries where the product is sold. Most countries around the world today have some sort of EMC regulations. Unfortunately, the problem with regulations is that they very carefully set the desired limits and test procedures for EMC but offer no guidance on how to meet these limits. These regulations also don’t tell you why the limit is important. The task of making a product meet the regulations usually turns into a test engineering task rather than a design engineering task. The engineer will design the application using normal design techniques and try to compensate for EMC. The product then goes through the test phase where most of the issues are resolved. 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

EMC与EMI / RFI 一般通常称为EMI或RFI EMI 是指电磁干扰 RFI 是指无线射频干扰工程师们创造了 EMC 这个术语, 用来正面地表达这些情况 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

EMC的组成源 (发射器) 传输途径 (耦合) 受体 (接收器) EMC is concerned with the generation, transmission and reception of electromagnetic energy. These three things define the scope of EMC design. The source (or emitter) produces an emission, and the transfer or coupling path transfers that emission energy to a receptor (or receiver) where it produces a behavior. Sometimes this behavior is intended such as a RF receiver. Or it can be unintended such as a microcontroller resetting. Interference occurs if the energy received causes the receptor to behave in an abnormal manner. The transfer of energy causes interference only if the received energy is of sufficient magnitude or frequency to cause unintended operation in the receptor. The focus is on the way the receptor processes the received energy. One example of intended reception is a radio station broadcasting a signal and your radio receives it when tuned to the transmission frequency. If another radio tuned to a different frequency receives this transmission, it is unintended or actually the emission is intended but the coupling path is not. An example of an emitter whose emissions are always unintended are from a fluorescent light. 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

预防干扰分组射频辐射噪声元件 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

预防干扰分组射频敏感性可能的敏感元件 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

预防干扰分组传导辐射噪声元件 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

预防干扰分组传导敏感性可能的敏感元件 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

EMC常见举例 ESD - 静电放电静电电荷在应用系统和其它系统之间传递 This figure shows a person walking across some carpet and building up static charge on his body. If he touches the computer, an arc is created from his finger to the computer and this built up charge is transferred to the computer. This transfer of charge can cause permanent damage to the Ics inside the computer. The arc itself can cause an electromagnetic wave to travel across the computer which can couple onto the internal circuits of the computer causing operational errors. 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

EMC常见举例 EMP - 电磁脉冲核爆炸产生强烈的电磁波 During the first nuclear testing in the mid 1940s, it was found that semiconductor devices in devices that were used to monitor the blast were destroyed. It was not due to the physical effects of the blast such as the explosion but caused by an intense electromagnetic wave. This wave was created by the separation of charge and movement inside the detonation itself. Polling question The same principles used to reduce the effects of radiated emissions from adjacent systems also apply to EMP but on a much larger scale. 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

EMC常见举例闪电被闪电间接地击中 Lightning occurs all around the world and direct strikes are frequently encountered. It is, however, the indirect effects of the strikes that damage electronic systems. Lightning can carry up to 50,000 Amps of current. The electromagnetic fields generated by this current can easily couple into electronic systems by direct radiation onto the system or coupling to a cable such as the power cord for the system. A system designer would need to prevent the resulting transient voltages and/or surges that lightning generates. 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

解决EMC问题的成本解决EMC问题的成本 The longer you wait to fix EMC issues, the more it will cost to fix them. For example, if you find an EMC problem during testing, you will need to fix the problem on a board (which can be costly) and then retest the board which is another additional cost. 概念设计布线原型测试生产 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

条例 FCC-联邦通讯委员会 IEC - 国际电工委员会军事医疗运输工具其它 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

FCC 重点放在辐射上任何无意放射源(器件或系统), 以每秒 9000 脉冲 (周期)的速率产生和运用时间脉冲,同时使用数字技术… 定义两种类别 A 类: 运用在贸易、商业或工业的环境中 B 类: 运用在家用环境中,但也包括运用在贸易、商业或工业的环境中 This digital device can be any electronic device that has digital circuitry and uses a clock signal in excess of 9KHz. Includes things like printers and computers. It is illegal to market a digital device in the US unless it meets the FCC limits. Marketing is considered to be shipping, selling, offering for sale, etc. It is a very broad term. Class B limits are more stringent than Class A limits because it is assumed that interference from a device in an industrial environment can more easily be corrected than in a residential environment. It is also further assumed that the residential customer does not have the expertise or financial resources to correct the problem as an commercial or industrial customer. 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

FCC 第15章 FCC关于射频和传导辐射的第15章是产品最相关的包括三个部分的内容 A: 一般要求 B: 无意放射 C: 有意放射对产品设定频率和强度限制 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

IEC 国际性的机构,为实现国与国之间的贸易制定规则规则集中在放射和防护两部分标准包括IEC x-x 同时包括CISPR 标准关于无线电干扰包括 CISPR 11, 22的国际特殊委员会两种标准基本标准包括特定干扰产品标准包括特定产品 The European community as well as other areas in the world follow the IEC specifications. The IEC has no legal authority to enforce the standards, it only maintains and helps generate them. The most common IEC standard is the IEC x-x and the CISPR 11 and 22 standards. These standards have two forms. The basic standard covers a specific interference type. The product standard covers a specific type of product and refers to the basic standards. IEC is the product standard for medical instruments. Other product standards exist for automotive and lighting. 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

IEC 标准 > 医疗电子设备 > 电磁兼容 > ESD > 辐射电磁场 > EFT/脉冲群 > 浪涌 > 射频场传导干扰 > 电压跌落和中断 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

IEC 标准 CISPR 11 -> 工业, 科技和医疗 (ISM) 的射频设备 14 -> 电磁兼容性 – 对家用器具, 电动工具和相似设备的要求 22 -> 信息技术设备 (ITE) 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

军用标准军用标准重点放在放射和敏感性两部分包括适用于以下领域的电子设备: 从潜艇到外太空从沙漠到绿洲电脑, 控制系统, 无线通讯标准是面向应用的标准是可以商议的 MIL-STD-461E 是关键的 EMI指标 Military standards are more concerned with mission success and could care less if the application interferes with a nearby television. Mission success means that the equipment must not interfere with vital radio communications and that same equipment must operate under severe conditions. Military specifications are very application specific depending on the application, environment and constraints. A tank has different requirements than a space craft or submarine. Weight is a concern for aircraft and space craft but heavy shielding is a requirement for tanks and submarines. The MIL standard address these issues with a range of tests and levels based on application, environment and even the branch of service. Another difference is that the tests and levels can be negotiated and waivers can be obtained. Based on the particular application, tests can be proved to be irrelevant and levels can be changes. The EMI requirements are not legal requirements but are contractual requirements. These limits are discussed before the design begins and can be modified or waived to best meet the applications requirements. 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

医疗标准最重要的是设备的安全可靠的操作主要着重于对射频电磁场,电源波动和ESD的防护在美国医疗器件是不受 FCC管制的没有强制的 EMI要求 FDA 推荐 IEC 60601标准欧洲运用IEC 60601标准标准是因应用而异的标准是基于泄漏电流的 Medical applications lie in benign to harsh EMC environments. The volumes are low to moderate so cost is not a critical issue. However, the cost of failure can be very high. Immunity is the primary focus with emissions the secondary. The focus of the standards is the safe and reliable operation of the application. The US does not have a mandatory enforcement of standards. Medical devices are exempt from FCC limits and rely on the FDA for regulations. The FDA recommends using the IEC standard. Europe mandates IEC The standard used depends on the application. A pacemaker for instance has a much higher standard than a heart monitor. Upsetting the operation of a pacemaker is life threatening. Upsetting a heart monitor may mean repeating the test. It is very common that the limits used for medical equipment are much higher than those found in military standards. The most severe restrictions are on current leakage. Devices that are directly connected to patients must limit the current leakage to prevent accidental microshocks. This presents interesting design challenges when you consider how a sensor or shield or filter is grounded. Medical standards are concerned with the leakage current that a patient would be subjected to when connected to the equipment. For instance, if you have a heart rate monitor, you don't want it dumping current into the patient. Therefore most of the standards have some level of current leakage that is acceptable. 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

运输工具标准是世界最严格的标准之一适用于飞机, 火车和汽车电子设备在极端恶劣的条件下操作同时也对成本非常敏感重点放在防护和放射两部分汽车工程师协会公布的标准 SAE J551 和 J1113 The vehicular standards are among the toughest in the world. Imagine designing a product that must endure temperatures from subzero to boiling, moisture, corrosion, petrochemicals, RF fields, ESD and power glitches. AND it must be at the lowest possible cost. Sort of a major conflict when designing electronics for cars. Some of the most igneous EMC designs come out of the automotive market. The standards are not mandatory but are usually required by the automobile manufacturer. They cover all aspects of electronics: from engine controls to AM/FM radios to cellular telephones. The environment covers both inside and outside the vehicle. The cost of failure can be low to high depending on the function. A radio failure is not usually life threatening but a failure in the air bag could be. SAE J551 primarily covers radio and TV emissions similar to the FCC emission limits. J1113 is more component level specific and applies to the electronic modules of the automobile. J1113 includes both immunity and emissions and is similar to the MIL-STD-461 spec. Often, the automotive manufacturer may have their own internal specifications based on the SAE standards. 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

其它标准 ANSI/ESD-S > 电力和电子器件, 组件和设备的保护 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

元器件的选择封装类型电阻电容旁路去耦振荡电感 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

封装类型有引脚或表面安装(SMT) 引脚长度和间距会影响器件的高频特性感性的 K K s K L 容性的 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

封装类型从EMC 的角度由好到差排列: 表面安装径向排列引脚轴向排列引脚引脚长度越短越好 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电阻电子系统中最常见的元器件具有多种类型: 碳膜电阻 - 用碳形成的圆柱体，并在两端有引脚线绕电阻 - 在圆柱形物体上绕导线薄/金属膜电阻 - 薄的金属膜沉积在绝缘体的两面，同时两端连有引脚 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电阻 SMT 电阻是最好的，因为它具有最小的引脚电感有引脚电阻碳膜金属膜线绕金属膜适用于高功率密度或高精度电路线绕电阻适用于高功率电路不要在高频敏感电路中使用 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电阻线绕电阻在高频情况下表现出更高的电感性在开关电源中的电流反馈电阻电流可能有很大变化或 di/dt v (t) = R*i(t) + L*di(t)/dt 可能导致反馈电阻给出一个错误的反馈电压也有高辐射的付作用在有快速的上升和下降沿的开关频率上，电阻上产生脉冲电压，并最终导致噪声的产生 Wire round resistors have high inductance due to the wire inside the resistor being wrapped around an insulator. If this type of resistor is used in the feedback loop of a switching power supply, you will have two effects. The first is that as the current is pulsed across the resistor, an additional voltage will be generated as shown in the equation. This voltage will cause an error in the feedback for the power supply. The second effect is that the pulsing current across the resistor typically happen very quickly and have fast rise and fall times. This will generate noise. 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电容电解电容 – 夹着一层薄的电介质的金属薄膜卷绕而成. 钽电容 - 一块电介质二端有金属及引脚陶瓷电容 - 在陶瓷电介质中的多个并列金属盘陶瓷电容和钽电容常用于 EMC 抑制低的电感和低的等效串联电阻（ESR） 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电容 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电容自身谐振 (f0) 感抗等于容抗感抗与容抗的值相等但符号相反电路网络的阻抗呈现出阻性 Impedance 容性的感性的 f0 f0 = 1/(2 LleadC) 频率 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电容为电流到地提供了低阻抗的泻放通道频率必须低于谐振频率有时需要多个电容来提供更宽频的滤波常见的错误是用更大的电容来解决问题 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电容谐振频率不同容值带引脚 SMT 1.0uF 2.5MHz 5MHz 0.1uF 8MHz 16MHz 0.01uF 25MHz 50MHz 1000pF 80MHz 160MHz 100pF 250MHz 500MHz 10pF 800MHz 1.6GHz 并不总是越大越好 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电容陶瓷电容容量一般较小即使到更高的频率,也可保持理想的状态中频到高频的滤波 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电容电解电容和钽电容较大的电容值低频滤波用于大量的电荷储存电解电容有更高的电感性钽电容有低的 ESR 具有低ESR的电容对信号的衰减较小 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电容旁路在不期望的频率到达敏感电路之前将它吸收观察共振频率以及高阻抗电路低阻抗负载会从旁路电容中吸收能量通常使用较大容量的电解电容或是钽电容 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电容去耦器件开关时会把噪音耦合到电源 (VDD & GND) 去耦电容在器件的电源上滤掉高频噪声应该尽量靠近器件的电源引脚陶瓷电容通常被用于去耦, 因为其快速的上升和下降时间以及低的 ESR 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电感开环: 棒状电感磁场穿过空气闭环: 磁环磁场穿过核心无寄生电感引脚器件和 SMT无差别 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电感阻抗 Rpar 阻性感性容性 Rpar 2L 1 2LCpar 频率自身谐振 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电感开环电感增加 EMI 闭环电感对外部噪声极不敏感两类磁芯材料铁: 用于低频 (kHz) 铁氧体: 用于高频 (MHz) 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

电感当使用电感来解决 EMC 问题时适用于直流信号或不常变化的信号低阻抗的负载并联电容更适于高阻抗负载铁氧体磁珠基本上是一个单圈电感在高频时提供 ~10dB 衰减在低频时的呈低衰减特性或阻性 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

线路端接处理使线路 (线路或电缆)的阻抗与负载相匹配阻抗不匹配会产生反射,振铃和过冲形成 EMI; 耦合到其它电路两种常用的类型: 串联并联 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

线路端接处理串联端接低成本和低功率增加对信号的延时在信号源端端接最大值不超过 100 Z0 RS 源驱动器负载 Cd RS = (Z0 - ZS) ZS ZL 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

线路端接处理并联端接低成本高功率对信号有小的延时在负载端端接典型值为 50 Z0 源驱动器负载 RP Cd Z0 = Rp // ZL ZS ZL 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

PCB 布线电路分割接地布线过孔断桩线宽环路 PCB 电容 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

PCB 布线电路分割物理的分割电路来减少耦合大电流或高开关频率电路应该靠电源越近越好 VCC GND 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

PCB 布线接地地是电路中的理想参考电位在实际中, 寄生电感和大电流在地线区域引起变化两种常用的接地技巧单点接地多点接地 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

PCB 布线模拟地和数字地数字电路产生很多噪声在单点分别供电和接地,通常是在电源端数字供电 VDD 数字数字地 AIN 模拟数字模拟供电 AIN 模拟 GND 模拟地 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

PCB 布线过孔 - 避免在高速信号上每一个过孔的阻抗 ~2nH & ~0.5pF 引起阻抗不匹配和信号延迟避免通孔和过孔的集中使电源/接地层有更高的阻抗很多噪声在此区域产生 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

PCB 布线断桩 - 避免在高速信号上以减少反射 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

PCB 布线尖角转角应该避免使用于高速信号内部的边沿产生场 >3T On a trace that has a right angle corner, it creates an impedance mismatch. In the case of the right angle corner, this causes a field to be produced on the inner edge of the corner which creates noise or emissions. The figure shows the proper minimum dimensions to create 45 degree corners in traces to minimize noise and emissions. 45 degree corners have lower emissions than right angle corners. 45° T 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

PCB 布线线宽在整个信号通路保持恒定的线宽任何变化都会引起阻抗的不匹配 Add picturesof examples 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

PCB 布线环路对于高速信号应尽量减小环路的面积尽量减少回路中的噪声回路 Add picturesof examples 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

PCB 布线 PCB 电容单层板: 电源和地平行走线多层板: 2 个相邻的层, 一个用于电源一个用于地均匀分布的去耦电容有助于取得较高的频率响应和较低的感抗双面 PCB 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

PCB 布线通用规则使用去耦电容使用去耦电容!! 使电源和接地线/层越大越好降低阻抗分离或屏蔽高频线路以减少串扰把所有没有用到的铜箔接地 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

微控制器电路电源 I/O 口中断引脚复位引脚振荡器 EMC 保护/预防 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

微控制器电路电源任何电源上的噪声都会窜入到板上的所有电路必须有充足的去耦电容和大电荷储存电容使用有电源层的多层 PCB 板减少环路区和降低阻抗大部分成本敏感的应用都使用单面板或双面板必须在其它采取EMC措施 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

微控制器电路 I/O 口所有未用的输入端应该用电阻接到 VDD 或 GND (4.7K 到 10K) 对于靠近静态信号、复位引脚、中断引脚和振荡器电路的高频输入或输出信号要小心布线在敏感的输入引脚上的耦合电容可以帮助衰减高频噪声 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

微控制器电路中断引脚边沿触发中断对噪声很敏感使用电平触发型中断或在 ISR内部采样中断引脚使用端接技术来减少反射,振铃或过冲,以避免错误的中断对于与中断相关的线路/引脚要小心处理以减少串扰 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

微控制器电路复位引脚推荐使用一个 <1K 的串联电阻来限制由ESD 或EOS 引起的进入MCLR复位脚的总电流推荐使用一个去耦电容来衰减高频噪声推荐使用<40K的到VDD的上拉电阻 PIC18FXXXX MCLR/Vpp VDD 10K 0.1F 100 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

微控制器电路复位引脚 MCLR 同时也是烧写时的 Vpp 引脚如果不使用在线串行编程(ICSP™)的话，就加一个到Vdd的二极管以提供额外的ESD保护 PIC18FXXXX MCLR/Vpp VDD 10K 0.1F 100 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

微控制器电路振荡器振荡器电路通常具有高阻抗对高频信号串扰或噪声都很敏感可导致频率抖动、超标的占空比或停振建议使用保护接地环 VDD VSS OSC1 OSC2 RC0 RC1 RC2 28- 或 40引脚器件 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

微控制器电路 EMC 保护/预防大部分不期望的情形是由于超限使用微控制器所造成的当器件的线宽缩小时, 它们变得更敏感正确保护微控制器的输入/输出二极管, TVS, 串联电阻, 等等正确保护系统的输入/输出电缆, 屏蔽, 等等 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

软件周期性的刷新端口查询输入采用令牌传递技术或子程序计数器技术采用看门狗技术已知的复位循环把没有用到的程序空间用 goto $填充计算程序存储器的校验和 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

EMC 参考资料 Digital Design for Interference Specifications David L. Terrell & R. Kenneth Keenan ISBN X Introduction to Electromagnetic Compatibility Clayton R. Paul ISBN The Designer’s Guide to Electromagnetic Compatiblity by Daryl Gerke and Bill Kimmel EDN ( 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

EMC 参考资料 Noise Reduction Techniques in Electronic Systems Henry W. Ott Interference Control in Computers and Microprocessor-Based Equipment Michel Mardiguian ISBN AN1050, AN1263, AN Motorola 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

标准网站 Federal Communications Commision International Electrotechnical Commission MIL Standards (military) Society of Automotive Engineers 720 EMC Designing PIC® MCU Circuits for EMC/EMI Compatibility

720 EMC PIC® 单片机的EMC兼容性设计.

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720 EMC PIC® 单片机的EMC兼容性设计.

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