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floating well PAD ESD problem?

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gsheng

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when PD/ND mode, there are two paths from pad to Vdd,
(1) PAD->NMOS->VSS->VSS ESD BUS-> Vdd to Vss NMOS(or diode)->Vdd;
(2) PAD->foating well of PMOS ->Vdd;
I don't know which path is the main path. does path 2 exist?
 

sunking

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why not add a pmos for the charge from PAD to Vdd?
 

gsheng

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Because the pad is like 3.3V torlance 5V PAD.

Added after 2 hours 5 minutes:

We can not only connect PMOS's bulk to core vdd. Otherwise it will leackage through juntcion diode.
 

Baiyawfan

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I think if PAD has a negtive ESD voltage,then path (1) is active,else if postive voltage,path (2) is active,right?
 

ranier

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In case of tolerant I/O ( floating nWell structure), there is no path of pad to vdd .

so path (1) is just available.
 

gsheng

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ranier said:
In case of tolerant I/O ( floating nWell structure), there is no path of pad to vdd .

so path (1) is just available.
Do you mean path(2) is available? I do want to know why?
 

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