ESD resistor question

[snafflekid]

The resistor is there to help keep the voltage on the gates of the input circuitry lower at the start of the ESD pulse, like an RC filter. The snapback device will see the full
ESD voltage and hopefully turn on before the voltage on the gate has risen to levels that can cause damage.

 

[prcken]

The resistor is there to help keep the voltage on the gates of the input circuitry lower at the start of the ESD pulse, like an RC filter. The snapback device will see the full
ESD voltage and hopefully turn on before the voltage on the gate has risen to levels that can cause damage.

right, as current limiting device

 

[dick_freebird]

The resistor is there to make a limited current for your
"backstop" clamps, so that they can be smaller -and- keep gate
ox protected in the case that the front clamp is overvoltaged
at higher ESD currents (Vclamp+Iclamp1*Rclamp1 will be
held down to Vclamp by the second stage).

Thin film resistors have a finite power-to-blow and you want
to understand this limit, or you may have a "gate fuse"
instead. I have been surprised by short-pulse power-to-blow
data before, thermal calculations are poor predictors of how
the incident energy partitions into the resistor and the
surrounding materials. In the lab you would take a pulsed
overstress series looking for the beginning of resistor drift,
and stay below that power density (watts per square micron)
and energy density (joules per square micron) - both, or the
most restrictive / largest resistor area.

Diffused resistors can take more of a wallop, they are
contact limited rather than self-heating limited, much higher
volume / thermal mass.

However a diffused resistor used in the ESD network needs
to comply with latchup rules because it can be a trigger site,
forward substrate injection or reverse breakdown to well /
substrate can inject trigger current in a powered-ESD
scenario.

 

[iliyana]

Re: dog bone resistor picture

i think there's no difference. i have seen plenty of designs using poly res. poly res are easier to fab.

Poly resistor is easy to fab..where most of ESD was designed with the poly resistor. But I'm more interested on ESD which is designed without the poly resistor & said that it is better than the ESD with poly resistor in terms of the switching. Can anyone explain or comment about this. I don't know how true it is...