Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Ethernet Centre tap capacitor on transformer

Status
Not open for further replies.

FreshmanNewbie

Full Member level 6
Joined
May 10, 2020
Messages
389
Helped
0
Reputation
0
Reaction score
2
Trophy points
18
Activity points
3,875
I'm using this IC with this Eval board as a reference

On page 5 of the Eval board, the centre tab capacitor on the transformer is 22nF.

When the value is changed to 100nF, it works OK. But if its 22nF, it doesn't work.

Can someone tell me what is the exact reason behind this and what would be the exact capacitor value?
 

Hi,

Please tell which capacitor you talk about: Give the number shown in the schematic.
Aso please tell what "doesn´t work" exactly means and how you tested it.

Klaus
 

Hi,

Please tell which capacitor you talk about: Give the number shown in the schematic.
Aso please tell what "doesn´t work" exactly means and how you tested it.

Klaus
C32 and C37 capacitors in the schematic.
Doesn't work mean, When I connect this PHY to the other device, the link doesn't work. Connection is not established. Sometimes, connection is established with errors.
 

Hi,

"the other device" is what?
I mean, maybe "the other device" is upset somehow.

From the schematic:
We talk about a 3.3V supply node.
on page4 left top, we see the distribution of the 3.3V supply to the VDD33TXRX1 and ...TXRX2 nodes.

So capacitor installed or not, there should be 3.3V.
Now if you install 100nF you just get a bit more stable supply = lower impedance, less ripple.

To debug this I´d use a scope and take some measurements at these nodes. Both with 22nF and 100nF to see the difference.
Indeed I can´t believe the system is that sensitive. I expect the root problem else where, maybe in a non stable power supply at all. Measurement should show.

Klaus
 
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top