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how to change BJT voltage limiter to mos voltage limiter in ESD protection

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steven_jun

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hi , in ESD protection , i meet some trouble. i have a circuit consisted with bjts to limit the value of the supply voltage ,
but now i must use cmos technology to realize the same function of the voltage limiter in ESD protection . diode and resistor can be still used.

what should i do ??View attachment voltage limiter in ESD.bmp
 

dick_freebird

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You could begin with simple substitution, but you run into
the problem that MOS VT varies way more than BJT Vbe,
in "make" tolerances, and about as badly with temperature.

You would need a shunt at the final devices which is not
there, probably because pumping the shunt BJTs into
saturation and staying there for free is a good thing for
ESD (spurious triggering from noise or leakage, not so much).

You know, there's about a bajillion papers on ESD supply
clamps out there, for the searching. Let alone books.
You might keep an eye out for superior triggering schemes,
because that one looks prone to be slow. Depending on
the application environment, you may want to overlay
a level triggered scheme as you show, with an edge
triggered one that keys on the unique dV/dt of ESD
events (perhaps also including a slow clamp to kill that
trigger-mode under powered operation, if you are going
to be exposed to high level fast supply transients in
use).
 

steven_jun

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i still do not know how i could change bjt to mos(pmos or nmos) to realize the same function.

in my application ,the supply is produced by internal circuit and is bonded to pin of package.
the supply produced by circuit is pulse voltage, so i can not use RC-CLAMP as ESD protection.

i want to use voltage limter to realize ESD protection. i find a circuit made with bjt device from a paper to satisfy my application.
i must use cmos technology in my project. so i need a help !! thanks!!

View attachment voltage limiter in ESD.bmp
 

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