resistors question(s)

[Jordy101091]

Hi all,

im currently doing a redesign of a PCB. To be honest I have use some parts of the eblock circuits just to make sure it would function properly.
I hope I'm allowed to do so, other wise correct me at this point .

But what I'm curious to know is what is the function in series with a signal trace. for example the MMC Card reader block. If you look into the data sheet of the device you can see 8 series resistors of 220 Ohms. What is the function of these resistors. Should Implement these resistors into my design.
Are these resistors use only used for communication lines.

Hope somebody can give me some explanation.

Thanks in advance,
Regards Jordy

[BChappy]

Hi Jordy,

It is to reduce noise. This can be due to impedance mismatch in track or devices that cause signal bounce or reflections. These can be mistakenly interpreted as extra pulses.
Though not in this instance as the MAX3002 is a level shifter, but mixed CMOS circuits also include these sometimes to limit the V.logic from exceeding supply.
As for copying, good designs share common attributes!
By that I don't advocate copying designs but the resistor in series is standard good practice...

Best Regards

Brian

[Jordy101091]

Thanks for your reply,
If I understand this right I can use these series resistors in any communication line.

Regards Jordy.

[BChappy]

Hi Jordy,

I did a search and found this online.
Please see attached file.
It is a little involved with detail.

Best Regards

Brian

[Jordy101091]

Thanks man,

This will help a lot with my future desings.
Again thanks for sharing.

Regards Jordy