Reverse ESD Discharge control

[lightning_bolt]

Hi,

I have a design which is suffering from ESD related issues. The design runs off both a lithium battery and a 14v DC supply and uses a simple Diode O-Ring type setup to switch between the two power sources.
It has ESD protection consisting of ESD / TVS diodes, on all external IOÂ’s (HDMI, USB, etc etc) as well as an RC circuit were applicable. All the electronics are housed in a plastic moulded case.

When an ESD pulse is sent from the outside to the device we have no issues. However, when the plastic case housing the electronics is energised while running off the battery, (by say rubbing it on the carpet) and the discharge runs from the case or DC input jack to a metal object we have hardware crash inside.

Has anyone had any experience with this “reverse” ESD type of discharge ?

Thanks for any help,
Jeff

 

[KlausST]

Hi,

ESD protection ... but still ESD problems....
Thus I assume you did something wrong.

We don't know what you did, unless you show us.

Klaus

 

[std_match]

First make sure that you don't have any unconnected inputs.
Next check for sensitive high-impedande nodes.

It it difficult to give more advice without some documentation.

 

[dick_freebird]

ESD is ESD, it can be either polarity of voltage /
direction of current.

A better choice of case materials might help.

All of that clamping may (?) prevent damage-level
ESD but it will surely not keep inputs or outputs from
being driven to the rails and slightly beyond. A powered
circuit could be induced to latch up, or a spurious logic
signal interpreted causing some sort of functional
interrupt.

 

[marce]

Sometime you have to use plastic for the cases, plenty of electronics in un-shielded plastic cases that work and work even if there is a ESD incident...
Layout is critical, the position of the protection is critical... But every design has its own intricacies, so for a more focued answer we need more information.