Some questions about ESD

Hi
1)Which PADs need ESD protection and which of them donot need ESD necessarily?Why?
2)Do we need seperated Power line for ESD and internal circuitry?Why?If it is possiable,PLS give some example like 3.3v(core)/5v(i/o) application and single 5v application.Do we need three power pads(3.3v,5v,esd) for the former?

leohart said:

Hi
1)Which PADs need ESD protection and which of them donot need ESD necessarily?Why?
2)Do we need seperated Power line for ESD and internal circuitry?Why?If it is possiable,PLS give some example like 3.3v(core)/5v(i/o) application and single 5v application.Do we need three power pads(3.3v,5v,esd) for the former?

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all pads need ESD protection because they are directly connected to the external world. the power of the ESD may be connected to the power of the circuit it is protecting. but of course that depends to the ckt designer. the best solution is to tie the ESD devices to the most positive supply and to the ground.

Hi,but I have seen that the esd used seperated power and ground line from internal ckt,what is that?

leohart said:

Hi,but I have seen that the esd used seperated power and ground line from internal ckt,what is that?

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the power connection will be tied at chip level...

(1) For those PADs have a big NMOS (for example: driver or switch) connected between the PAD and ground, they don't need additional first-stage ESD protection. However, special attention is still needed for big NMOS to follow ESD rule. The reason is this big NMOS can function as ESD device.

(2) Generally, it is not necessary to have a dedicated supply line for ESD except for some special cases. Usually, there is no big current in ESD during normal operation, so internal circuit can share supply traces with ESD with no problem.

road_0506 said:

leohart said:

Hi,but I have seen that the esd used seperated power and ground line from internal ckt,what is that?

Click to expand...

the power connection will be tied at chip level...

Click to expand...

Hi，does that mean we will have seperated power pads for esd and internal ckt,and they will be connected on pcb board?It seems that there are seperated analog and digital power pads in some mixed signal applications...But seems no seperated pad for esd power... I am quite confused about these sepetated power for either analog,digital or esd,any books or papers detail this?

Added after 9 minutes:

leo_o2 said:

(1) For those PADs have a big NMOS (for example: driver or switch) connected between the PAD and ground, they don't need additional first-stage ESD protection. However, special attention is still needed for big NMOS to follow ESD rule. The reason is this big NMOS can function as ESD device.

(2) Generally, it is not necessary to have a dedicated supply line for ESD except for some special cases. Usually, there is no big current in ESD during normal operation, so internal circuit can share supply traces with ESD with no problem.

Click to expand...

Hi,if big nmos between pad and gnd can be used as esd device(it is like a pn junction?I suppose),then can a big pmos between pad and vdd be an esd device too?there should be two esd devices for both positive and negative discharge.And the nmos should be diode-connected or just connect on its drain or source is enough?

for the second comment,I'm not clear with the purpose of special power trace for esd,It seems to provide huge current for esd protection from ur comment.

anyway,if there is good books or papers on seperated power systems for analog/digital/esd part of the whole mixedsignal chip,PLS recomment it~