[SOLVED] Is it possible to use a 27 mhz crystal with ENC28J60?

[Kounista]

hi everyone,

I know that the ENC28J60 is designed to work with a 25 Mhz crystal but is it possible to use a 27 Mhz?

The thing is, i can't find a 25 Mhz where i live and it will take me at least 15 days to have the 25 Mhz delivered. I don't want to be stuck because of such a basic component.

Can i use the 27 Mhz crytal to generate 25 Mhz? for example by adding some passive components to it?

Thanks!


I have another question and i didn't want to start another thread for it so here it is:

I am planning to use a Magjack RJ45 connector, and i have noticed that i needed a 5mm ferrite bead rated for at least 80 mA. Is the Ferrite bead really necessary? If not, what can i use instead of it? a resistor maybe?

the ferrite bead is represented by L1 in the schematic below:



**broken link removed**

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[FvM]

Can i use the 27 Mhz crytal to generate 25 Mhz?

Never.

Is the Ferrite bead really necessary?

The circuit may work with a jumper wire instead. A resistor would cause unwanted voltage drop.

 

[Kounista]

Hi FvM, thanks for the quick answer,

Just to make sure, when you say jumper wire you mean directly connect the concerned node to 3.3V right?

 

[FvM]

Yes. The ferrite bead is intended for supression of high frequency interferences. I may be needed to keep EMC regulations and prevent voltage spikes on your 3.3V supply to pass to ethernet output driver or vice versa. But the circuit can most likely work with it.

 

[Kounista]

Thanks, i'll make sure the ferrite bead will be included in my final design. But for now i'm gonna start testing without it once i resolve the 25 Mhz crystal issue..

Regards

 

[Kounista]

Hi everyone,

Okay, so now i managed to extract a 25 Mhz crystal from an old NIC. But i was surprised to find out that it had 3 pins instead of the usual 2 pin crytals that i used to work with. Will it still do the job? What's that third pin for? Is it a GND pin? If that's correct, do i still need the external 18pF capacitors?

The only thing that's written on the top of the component is this: 25.00KSS 9H

 

[alexan_e]

Does it look like a crystal or is it a ceramic resonator
Ceramic resonator - Wikipedia, the free encyclopedia

if it looks like a crystal maybe it is a crystal oscillator that has the supply voltage (vcc and gnd) and an output.
like this **broken link removed**

Alex

 

[Kounista]

Hi alexan_e, thanks for your quick answer,

It looks exactly like a crystal but with an extra pin in the middle, i noticed that some crystals were available in 2 or 3 pin configuration just like this one:

QUARTZ CRYSTALS,Wholesale custom QUARTZ CRYSTALS,HC-49U & HC--49T



Edit:

I read somewhere else that the middle pin is there for shielding purposes and that it can be connected to GND or just can be left floating..

Now that i looked more carefully to the extra middle pin, i think it's directly connected to the case, this strengthens the possibility that it must be connected to GND.

What do you think of that?

 

[alexan_e]

I think it is a normal crystal with just a third pin in the center which is connected to the metal case to ground the case easier
Take a look below the crystal ( the pin side) the 2 pins should be insulated from the case and the third one (the middle) should be connected to the metal case.

Alex

 

[Kounista]

Thanks!

I was editing my message while you answered me! Correct, the middle pin is directly connected to the case. Thanks again.