DP83822I: Scrambler setting

K.Hamamoto

Part Number: DP83822I

Our customer measured EMI noise on their board. They found some noise(high peak noise) around 60MHz~110MHz and it was from DP83822I.

Is there any way to reduce that noises? I found the function that as Scrambler function.

What register we should set to enable this scrambler function? (Is that PHYSCR[11]?)

Could you give any advice if there is any other way to reduce the noise?

Best Regards,

Koji Hamamoto

over 7 years ago

0 Aniruddha Khadye over 7 years ago

TI__Mastermind 18425 points

Hello Koji,

We do not recommend changing the internal scrambler settings of the PHY. We do however have a reference design that has passed EN55011 Radiated Emissions testing along with other stringent EMI EMC standard. Please refer to the following E2E post for more information:

e2e.ti.com/.../661865

-Regards,
Aniruddha

0 K.Hamamoto over 7 years ago in reply to Aniruddha Khadye

Guru 12155 points

Hi Aniruddha,

Thank you for the information. We can refer the information however could you advice me what should we check at first?
Layout ? or register settings?

We are going to start checking their board. However we do not know what is caused by this EMI issue on the customer board.

Regards,
Koji Hamamoto

0 Geet Modi over 7 years ago in reply to K.Hamamoto

TI__Mastermind 26320 points

Hi Koji-san,

Both schematics and Layout plays important role for meeting emissions. You can start with right decaps on VDD, VIO. You may also want to try ferrite beads on VDD, VDDIO to supress the noise.

Regards,
Geet

0 K.Hamamoto over 7 years ago in reply to Geet Modi

Guru 12155 points

Hi Geet-san,

Thank you for your reply.

I got more detail from customer. (Schematics and layout and spectrum waveform.)
Can we talk on e-mail? I can show those information.

Best Regards,
Koji Hamamoto

0 Geet Modi over 7 years ago in reply to K.Hamamoto

TI__Mastermind 26320 points

Sure address it to me and Aniruddha.

Regards,
Geet

0 K.Hamamoto over 7 years ago in reply to Geet Modi

Guru 12155 points

Thank you.
Could you give me your email address?

Regards,
Koji Hamamoto

0 Geet Modi over 7 years ago in reply to K.Hamamoto

TI__Mastermind 26320 points

Share you email, I will drop you a note.

0 K.Hamamoto over 7 years ago in reply to Geet Modi

Guru 12155 points

This is my address. hamamoto-k@macnica.co.jp

0 Ross Pimentel over 7 years ago in reply to K.Hamamoto

TI__Mastermind 23675 points

Thank you Hamamoto-san,

My colleagues will review the schematic.

0 K.Hamamoto over 7 years ago in reply to Ross Pimentel

Guru 12155 points

Hi

Thank you for your support. I am waiting for your email.

Best Regards,
Koji Hamamoto

0 Ross Pimentel over 7 years ago in reply to K.Hamamoto

TI__Mastermind 23675 points

Sorry Hamamoto-san.
I thought they had sent you their email.
I just sent you mine.

0 Ross Pimentel over 7 years ago in reply to Ross Pimentel

TI__Mastermind 23675 points

Hi Hamamoto-san,

Thank you for sending the document.
It looks like you are following our layout guide well.
There are some options you have to reduce the emissions:
1. Change the gain of the driver by using register 0x403
2. add 10 - 30pF decoupling on TD+, TD-, RD+ and RD- lines

I noticed that LED_0 and LED_1 do not have parallel pull resistors. These are required to ensure proper strapping.
Please see our LED section in the DP83822I datasheet.

0 K.Hamamoto over 7 years ago in reply to Ross Pimentel

Guru 12155 points

Hi Ross-san,

Thank you. I had discussing with the customer about your suggestion and got some question. So that, I will make new post.
Please close this post.

Best Regards,
Koji Hamamoto

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DP83822I: Scrambler setting