ESD protection - clamping diodes

[metRo_]

Hi,
I saw a project where there is a ESD diode http://www.onsemi.com/pub_link/Collateral/ESD9B-D.PDF to protect from the 12v source. How does this diode works to protect against ESD? And in that case per example why should I choose the ESD9B3.3ST5G or ESD9B5.0ST5G?



Thank you

[T3sl4co1l]

Er, it does what it says it does... clamps ESD?

Wouldn't be a good idea from a 12V supply, they're basically 3.3 and 5.0V zeners (respectively).  Wired in pairs back to back, to get the bidirectional behavior.

Note that the clamp voltage is more like 10V under transient conditions -- there's no such thing as absolute "3.3V and nothing more".  It wouldn't be a great idea to connect one directly across a sensitive logic input, for example, but it would be fine with a series resistor inbetween.

Tim

[metRo_]

is is the circuit where i saw it:
i0.wp.com/andybrown.me.uk/wk/wp-content/images//awreflow/power_schematic.jpg

[T3sl4co1l]

Well, it ain't gonna be 12V for long.

Tim

[metRo_]

why you said that?

[T3sl4co1l]

The diode is shorting the supply above 9V or so.