[SI-LIST] Re: ESD protectioin at a Digital Input

Follow the current.  Observe the voltage.

Steve.
Vinod Kumar wrote:
> Hi All,
>
> For handheld battery operated devices, we don't have a  GND EARTH normally. 
> So in this case how should we connect the ESD device?
>
> We generally have a separate noise GND and all the ESD devices are 
> terminated to this. This GND is connected to signal GND at one point. But as 
> explained at  http://emcesd.com/tt2009/tt020309.htm , if the common GND 
> point is far away from ESD device, it can render the protection ineffective.
>
> But if a large single GND plane is used and all the ESD devices are 
> connected to this ground, the excess energy will be shunted to this GND. 
> Will this not affect the other devices through GND pins of ICs which do not 
> have any ESD protection (as all the devices are using same GND)?
>
> Thanks in advance for your suggestions.
>
> Regards,
> Vinod
>
>
>
> ----- Original Message ----- 
> From: "Doug Smith" <doug@xxxxxxxxxx>
> To: "Vivekkumar M-ERS,HCLTech" <Vivekkumarm@xxxxxx>
> Cc: "Arun Kumar P N" <arun@xxxxxxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> Sent: Thursday, December 10, 2009 12:06 AM
> Subject: [SI-LIST] Re: ESD protectioin at a Digital Input
>
>
>   
>> Hi Arun, Vivek, and the group,
>>
>> The board layout can easily erase any protection that the protection
>> device offers. The actual voltage the IC sees can easily be 10, 100 or
>> more times the clamp voltage depending on the board layout. One such
>> layout problem is described in my Technical Tidbit for February 2009:
>> http://emcesd.com/tt2009/tt020309.htm .  However, there are many ways to
>> render the protection device ineffective.
>>
>> Doug
>>
>> Vivekkumar M-ERS,HCLTech wrote:
>>     
>>> Arun Kumar,
>>>
>>> Clamping voltage of an ESD should be closely related to the voltage max 
>>> the pin of the IC can withstand. Even though the IC supports 1KV ESD 
>>> protection, check with the manufacturer about the max voltage the pins of 
>>> the IC can withstand. Say manufacturer suggests 10V. Then at max you can 
>>> have 15V as clamping voltage.
>>>
>>> The danger of having 200V voltage as clamping voltage is that when a 
>>> large surge occurs, the IC is subjected to this much voltage and it may 
>>> damage the IC.
>>>
>>> ESD diodes, another the important factor we need to consider is how much 
>>> energy(power dissipation in wattage) it can withstand. This is based on 
>>> the open and short circuit voltages and were your end equipment is 
>>> placed.
>>>
>>> Find attached app note from semtech.
>>>
>>> http://www.semtech.com/images/datasheet/transient_immunity_standards_iec_61000-4-x.pdf
>>>
>>> Regards
>>> Vivek
>>>
>>> ________________________________________
>>> From: si-list-bounce@xxxxxxxxxxxxx [si-list-bounce@xxxxxxxxxxxxx] On 
>>> Behalf Of Arun Kumar P N [arun@xxxxxxxxxxxxxxxx]
>>> Sent: Wednesday, December 09, 2009 4:16 PM
>>> To: si-list@xxxxxxxxxxxxx
>>> Subject: [SI-LIST] ESD protectioin at a Digital Input
>>>
>>> Hi All,
>>>
>>>
>>> I'm checking for ESD protection at a Digital Input pin.
>>>
>>> A Switch is connected to a Schmitt Buffer. The Schmitt buffer is ESD 
>>> rated
>>> for 1000V HBM
>>>
>>>
>>>
>>> I'm planning to put an external suppressor for IEC levels, on the PCB
>>>
>>> My understanding is the clamping voltage should be less than the max
>>> withstand capability of the pin to be protected.
>>>
>>>
>>>
>>> Since it has internal protection of 1000V, does that mean I can put a
>>> suppressor with a clamping voltage of say 200V?
>>>
>>>
>>>
>>> Or should I use an ESD suppressor with a clamping voltage well below 10V?
>>>
>>>
>>>
>>> Regards
>>>
>>>
>>>
>>> Kumar
>>>
>>>
>>>
>>>
>>>
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>> -- 
>> -------------------------------------------------------
>>    ___          _       Doug Smith
>>     \          / )      P.O. Box 1457
>>      =========          Los Gatos, CA 95031-1457
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>> /  /\  \ ] /  /\  \     Mobile:  408-858-4528
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