Help me identify capacitor + HDMI ESD protection question

[MCH]

Hi,
I am trying to reverse engineer a PCB and it has a few of these parts labelled as capacitors. I am a complete noob and i have never seen capacitors like this. The picture is not very good but they are green with something like a circle in the middle and look more like LEDs or diodes.

I have spent quite some time in google but i have not find anything similar. The closest are SMD film capacitors, but the ones i have seen always have a line pattern, not this circular inner shape.

My multimeter can measure down to at least 100 nF without problem but doesn't see these ones, they must have a very low capacitance.
They are part of a 5V to 1.8V circuit within the board, something like this:

the capacitor in question is the one with the question mark.

 

[DVDdoug]

Since you'll also need to identify the chip, check the manufacturer's datasheet for the recommended circuit design. (Or choose a different chip and don't bother exactly-duplicating the existing design.)

It's on the 5V input so the value isn't that critical. (It's not part of a tuned filter or part of the oscillator.)

Electrolytic capacitors don't "act like" capacitors at high frequencies so it's common to put a ceramic capacitor in parallel with the electrolytic. 0.1uF should be fine.

Or if it's REALLY for ESD protection it could be a transorb.

Were you able to identify the inductor?

 

[MCH]

Thanks dvddoug.
Unfortunately I need to stick with this chip and I don't have access to the datasheet, but I hear your suggestion of a smaller ceramic. I am still curious what this green thing is though.

No, the ESD protection is an unrelated question I will post later on.

Thanks again

 

[sq225917]

Doesn't look like a cap, looks like it had 'legs' so could be a diode.

 

[Sokel]

Looks like a cap to me:

 

[MCH]

Looks like a cap to me:



View attachment 297828

Yes, that seems to be it!!
And, is it just like a regular capacitor? Can I just use a normal ceramic one instead?

 

[Sokel]

Yes, that seems to be it!!
And, is it just like a regular capacitor? Can I just use a normal ceramic one instead?

There must be a reason to put a specialized cap like this there.RF?
Way above my pay grade but I would try to find a same one to put there.

Is there something wrong with the one you have or you just want to duplicate it in another pcb?

 

[MCH]

There must be a reason to put a specialized cap like this there.RF?
Way above my pay grade but I would try to find a same one to put there.

Is there something wrong with the one you have or you just want to duplicate it in another pcb?

well, i have the ones i savaged from the original pcb that i can reuse, but they are 0603 and look so flimsy... I would prefer to have an alternative in case, but i can live with that, no problem.

 

[MCH]

Regarding the question about the HDMI ESD protection.

The same PCB of post #1 is for a HDMI audio card i am trying to build.

I read that it is recommended (even mandatory to comply with the standard? not sure though) to add ESD protection to HDMI connections to avoid damaging the devices when plugging/unplugging. These are usually the very little ICs that you see just besides the HDMI sockets:

I also see that quite often manufacturers just skip them straight away, even leaving the footprints in...:

bad boys...

Now, in my case, this will be a diy device for personal use, and the source (a raspberry pi), will be at the same time the HDMI source and the power source for the HDMI receiving card, that is, they will share a common ground.

My question is:

In this situation, with both circuits electrically connected, is there any chance that a ESD event happens? can i just skip the ESD protection? it would make my project easier....

thanks again for any comments.

 

[Doodski]

In this situation, with both circuits electrically connected, is there any chance that a ESD event happens? can i just skip the ESD protection?

Discharge can happen anywhere at any time is the rule with ESD. It cannot be stopped it can only be minimized and controlled by dissipating the charge slowly to ground so as to prevent high discharge rates. If your unit is powered ON and somebody walks up with a full charge and they zap your gear there's little to nothing you can do other than using ESD safe floor waxes, ESD mats, grounded workstations, ESD wrist straps and ESD clothing. If you can add circuitry that increases ESD safety then it is a wise addition to the connector. I zapped electronics with a major charge and lost 2 KEF tweeters in the process. I would use the ICs

 

[MCH]

Discharge can happen anywhere at any time is the rule with ESD. It cannot be stopped it can only be minimized and controlled by dissipating the charge slowly to ground so as to prevent high discharge rates. If your unit is powered ON and somebody walks up with a full charge and they zap your gear there's little to nothing you can do other than using ESD safe floor waxes, ESD mats, grounded workstations, ESD wrist straps and ESD clothing. If you can add circuitry that increases ESD safety then it is a wise addition to the connector. I zapped electronics with a major charge and lost 2 KEF tweeters in the process. I would use the ICs

Understood, thanks.
I was thinking these protection ics were only there to stop ESD coming from the connected devices, and was wondering what is the point in my case, when the two devices are electrically connected anyways...

 

[Doodski]

Understood, thanks.
I was thinking these protection ics were only there to stop ESD coming from the connected devices, and was wondering what is the point in my case, when the two devices are electrically connected anyways...

Not sure what you mean by, "When the two devices are electrically connected anyways." But that connection is what you are trying to protect and enhance by using the ICs. Just because they are connected does not mean ESD is not present or cannot occur. The cable if in the path of discharge is a direct entry point for the ESD to damage something. Check out these webpages for images of actual ESD damage at components. It causes real and lasting damage.

Microcircuit ESD Damage

NASA Electronic Parts and Packaging (NEPP) Program Website

nepp.nasa.gov

https://sma.nasa.gov/docs/default-source/sma-disciplines-and-programs/quality/qlf/nasa-eee-parts_esd_compendium_june-2018-sept-18.pdf?sfvrsn=551c0f8_0

 

[MCH]

Not sure what you mean by, "When the two devices are electrically connected anyways." But that connection is what you are trying to protect and enhance by using the ICs. Just because they are connected does not mean ESD is not present or cannot occur. The cable if in the path of discharge is a direct entry point for the ESD to damage something. Check out these webpages for images of actual ESD damage at components. It causes real and lasting damage.

Microcircuit ESD Damage

NASA Electronic Parts and Packaging (NEPP) Program Website

nepp.nasa.gov

https://sma.nasa.gov/docs/default-source/sma-disciplines-and-programs/quality/qlf/nasa-eee-parts_esd_compendium_june-2018-sept-18.pdf?sfvrsn=551c0f8_0

Thanks again, Doodski.
For clarification: the HDMI source will be a raspberry pi, that besides being connected to my device via HDMI, will be also powering it via 5v/ground header pins. That's what I mean with "they will be electrically connected anyways". Sorry for the confusion.

 

[Doodski]

Thanks again, Doodski.
For clarification: the HDMI source will be a raspberry pi, that besides being connected to my device via HDMI, will be also powering it via 5v/ground header pins. That's what I mean with "they will be electrically connected anyways". Sorry for the confusion.

ESD can be anywhere. It really is a nemesis of electronics in that it can migrate on surfaces to new locations, travel across the floor, build up on your sleeve and travel down your arm to your hand etc. ESD does not care about electrical energy being present in circuit and it only requires a discharge to boost the voltages into the thousands+ of volts. So a connection/HDMI connector point is to ESD just a opportunity to get into more stuff and do what ESD does which is be a pain in the butt.

 

[Sokel]

I was laying on the carpet in my previous house once and when I got up and touched the pot of my pre I zapped it to the point it blown it's fuse.
It was scary!

 

[MCH]

Well I do have an ESD safe lab coat at work, but the laughing of my family if I start using it at home when tinkering with my stuff could get louder that all the fuses exploding simultaneously