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Prevent from ESD damage by a parallel inductor?

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bagel520

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esd inductor

Hi all,

Why adding an parallel inductor after antenna can prevent RF circuit from ESD damage?

Thanks!
 

bagel520

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cdm requirements for saw filters

Hi! kspalla,

Please see attached file.

"A simple inductor to ground at the antenna port (see Figure 1) will normally provide adequate protection of a SAW device. The inductor shorts most of the ESD voltage to ground."
 

FvM

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inductor esd

inductor can not do ESD protection
Sure it can. Perhaps not reliably in case of fast, high energy transients, but it will at least provide some protection. Quarterwave stubs are the most effective protection, by the way. They can even stand direct lightning influence, in combination with a suitable second level protection.
 

bagel520

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esd protection shunt inductor

Hi! FvM,

Thanks for your response! Could you please explain the reason why an inductor can help prevent from ESD damage? I've heard ESD behaves as a high frequency energy. How an parallel inductor can help divert high frequency energy to ground?
 

FvM

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shunt inductor esd

Standarized ESD test pulses have us rise time and duration. So in case of an UHF antenna and a suitable low inductance, it is reduced to much lower voltage and energy. But as I said, fast rising pulses (e.g. contact discharge test pulse) can still be dangerous to the device.

On the other hand, without an inductor, even a slow rising DC voltage (static electricit without a discharge) can damage the receiver.
 

FvM

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The attachment says something different: The Inductor is good for a SAW filter (that has some intrinsic ESD strength) but not sufficient for a ESD sensitive MMIC. In the latter case, the inductor is used in a resonant circuit with the protection diodes.
 

srftech

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Hi Everyone,
Apart from the use of the inductor in the role of the matching network, and focusing solely on its role during an ESD event, here is how it needs to be viewed.

The inductor will provide a path to ground (Assuming we are talking about a shunt inductor between the protected node and the primary ground) for a good chunk of most ESD energies. BUT....

ESD events are like snow flakes, and no two real events are the same. That is why in the industry we have several standardized test models (HBM, CDM, and MM...to name the most common) in an attempt to qualify products against the majority of ESD events that they would experience in the real world.

The shunt inductor's effectiveness completely depends on its actual inductance and impedance relative to the ESD event, but as a simple rule of thumb (this is not official but works well in a hand waving approach, take it with a grain of salt), HBM type events have ESD energy below <5MHz, MM <15MHz and CDM >1GHz...so you see, an inductor may work well for some ESD events, but not for others (Note CDM especially) in which case the inductor would serve little help at all.

PS: Most ESD events experienced by products in modern assembly lines are CDM like in nature.

Excellence in ESD and IO Design
 

    bagel520

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Joel-Tang

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It all depends on what voltage will damage the part you are trying to protect. An inductor will shunt the energy and the higher the inductor value the higher the initial voltage spike.

I love devices that only need an inductor. . . . Series capacitors also are used in some cases.
 

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