Noice from TCP line, why?


Dear Wiznet

We have a product base on W7100A. We followed closely your recommendations in iMCU7100EVB Rev 1.1. Now we are facing with a problem of noise. We noticed that in some of our products there are noises from TCP line (8 modules among 90 modules).

Please help us in troubleshooting this problem.

We provide below parameters of components that are different with the schematic in iMCU7100EVB Rev 1.1.
In our schematic:
CP3=22 uC/16V
CP4=22 uC/16V
CP5 =47 uC/ 16V
CP7= 22 uC/16V
FB5= two inductors 4.7 uH (in parrallel) (We noticed that if we touch the point after FB5 by our bare hand, almost always W7100A resets. Interesting, why?).
FB1= two inductors 4.7 uH (in parrallel)
(Note: FB1=two inductors (0805) 4.7uH in parrallel, each has current rating:50mA. I personally think that this current rating is too low, but I have not found any heat from the inductors. So maybe there is no problem in using them) (in Vietnam it’s hard to find exactly components that we need, so sometimes we use components with different electrical characteristics).

Best regards,
Dat Bui
Hanoi, Vietnam
iMCU7100EVB_Rev1.1_Schematic.pdf (39.3 KB)


Please check voltage of 1.8A line if it is too low. I recommend to ferrite beads or short( through Oohm resistor).
Addtionaly, I recommend to replace FB5 to High-voltage of capacitor(1nF/2kV)
for a discharge path from chassis ground through it for ESD.



Dear Peter,

We measuared the voltage 1.8 V, saw that the voltage is 1.7-1.9V. We think that is normal.

We replaced the FB5 with a capacitor 1nF 2kV, but it does not help.

We found another problem with the eletrified metal cover of our product.

we measured and see that there is voltage around the hole for Hanrun.
Please see the capture of ossciloscope.

So when we use a electric plier to touch to metal cover of Hanrun, Wiznet W7100A resets immediately.

We are wondering, why does this happen? (please note that it does happen in modules with FB5 are inductors, and FB5 are capacitors of 1nF 2KV.
If there is voltage of electric charges around the hole, does it affect aging of W7100A? Does it kill W7100A after a period of time of usage?

We are wondering much, and are very concerned about this phenomenon.
Please help us in troubleshooting this.

Best regards,
Dat Bui
Hanoi, Vietnam


In this case, we are also difficult to find the cause.
And I don’t think it is affect to aging of W7100A.

…I suggest TVS diodes using at each Ethernet data-lines(TX+/-, RX+/-).