EMC设计技巧及经验总结3：TVS的使用-白红宇

EMC设计技巧及经验总结3：TVS的使用

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发布时间：2019-04-28

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Way back in undergrad circuits class（回到本科时的电路课程）, our TA（助教） loved to give us

little “black box” circuits. We’d measure the voltage and current characteristics, then

have to determine what components made up the circuit. Our TA particularly loved to throw

diodes in there. At the time I couldn’t figure out why, as I didn’t see much purpose in

diodes. However, I did come to appreciate diodes when I was looking for ways to protect my

PCBs from electrostatic discharge（静电放电）. Diodes are a crucial component for managing

voltage levels, which is a critical effect of electrostatic discharge (ESD).（中文大意：回想本科时的电路课程，我们的助教喜欢给我们一些黑盒子的电路，我们测量电压电流，然后决定使用什么器件搭建我们自己的电路。在这个时候，我们不理解为什么使用很多的二极管，不知道它的具体用途。现在，我们知道了这些二极管可以用来防止静电放电，以保护PCB。二极管是一个电路组件用于管理电压等级，他对于ESD有显著的效果。）

ESD can come from many sources, even just an inadvertent（疏忽的） touch, and cause a voltage discharge that wreaks（发泄） havoc on your board. One of the most common sources of ESD is at inputs, like cables being plugged in or buttons being pressed. Here, you’ll want to minimize the voltage spike（毛刺） that will reach your sensitive components.（ESD有很多产生源，例如不经意的接触，就会引起电压放电以损坏我们的线路板。在这些产生源中有一种是输入源，例如线缆的插接，按键的按下。为了保护敏感组件，我们需要削减这种电压毛刺。）

When you add a TVS to your design, you want to smooth out your traces as much as possible to minimize any EMI generated at corners and propagating across the board. The Texas Instruments recommendation is to use large radius curves instead of corners. If you can’t because of the PCB technology, then use a maximum corner angle of 45°. To me, it looks like a 135° angle, where instead of a right angle, you cut off the corner, like a stop sign, and have two very obtuse angles instead. Also, I highly recommend TI’s Technical Resources section when you really need to get down in the weeds to solve a problem.

（当你在设计中加入TVS时，最好能够柔滑走线，以最大程度的削减EMI在边角产生并在线路板上穿越。TI公司推荐使用大半径曲线代替边角。如果由于自身PCB技术的缺陷，你可以按照下图进行走线设计。不过，我高度推荐TI的技术源。

）

While

we’re on the subject of traces - you should avoid using a VIA to connect the ESD source (your input) to the TVS if it is at all possible. Stick to traces for the TVS, since VIAs can really complicate ESD protection. When you’re so close to a likely source of ESD, it’s a mess

you don’t want to get into.

（当我们谈到走线的话题时，应当避免使用过孔去连接TVS和ESD源，过孔会恶化ESD效果，这是你不想进入的混乱局面。）

Finally, you should also include a buffer resistor in your protection circuit. You add it in series between the possible ESD source and the IC you’re trying to protect. That helps decrease the peak current that will reach the IC from the current divider you’ve added at the input. Some TVS diodes can “reset” themselves from a massive voltage spike, but not all. If they’ve been cooked from a discharge, they might short to ground and eliminate any protection you were getting from the TVS. Diodes are mighty, but it’s good to have a second line of defense. （也可以通过加入缓冲电阻的方式，以保护我们的电路，它可以降低到达IC的峰值电流。TVS已然很好，不过也可以加入第二道防线。）

有任何问题欢迎留言，我尽最大可能予以解答，知而获智，智达高远。

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