[SI-LIST] Re: ESD protectioin at a Digital Input
- From: "Vinod Kumar" <vinodsaharan@xxxxxxxxxxxxxxxx>
- To: "Doug Smith" <doug@xxxxxxxxxx>, "Vivekkumar M-ERS,HCLTech" <Vivekkumarm@xxxxxx>
- Date: Tue, 15 Dec 2009 21:00:51 +0530
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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