What and why is this component across an isolation barrier?

[AlfBaz]

In this post is a picture of the internals of an M-131 Maynuo RS232 isolator

The isolation barrier is across IC2. Is that blue component a cap, a MOV or something else? I cant, for the life of me, figure out what it's doing or why you would put it there

[Stonent]

It looks like a MOV but is labeled C10 as if it was a capacitor.  The IC underneath is likely a optocoupler/optoisolator.

[AlfBaz]

Ahh, didn't see C10 under the shadow
In that thread they've come to the conclusion its an ADUM2201 digital isolator.

Still don't know why its there. Are they trying to protect the isolator from transients by dumping it onto the pc's ground?

[lgbeno]

It's a Y capacitor, purpose is to allow a high frequency path between the two grounds.  It is a typical thing to do in systems to pass emc testing

[Rufus]

Ahh, didn't see C10 under the shadow
In that thread they've come to the conclusion its an ADUM2201 digital isolator.

It is more likely one of their isoPower isolators (like ADuM5201) which include an isolated DC-DC converter running at 180MHz.

Such converters end up being an rf signal generator between the two grounds and it needs to be shorted out with some capacitance to reduce radiation from one ground with respect to the other. On multilayer boards you might get enough capacitance by overlapping the grounds on different layers. If not you have to add capacitance and placed across the isolation barrier it needs to be rated accordingly.

[T3sl4co1l]

The internal monolithic transformers are pretty good already (they use balanced drive), but a cap may help with EMI from the device, or just for external purposes because -- cables resonate, and added capacitance means you get a lower impedance for ferrite beads to work against.

Tim