DP83TC813S-Q1: Crystal Xi and Xo series resistor Value recommendations and Crystal load cap recommendations

Kallikuppa Sreenivasa

Part Number: DP83TC813S-Q1

Tool/software:

Hi Experts,

We have some schematics review requests where customer are using DP83TC81x devices including DP83TC813 or DP83867 with crystal (On the SKs we currently use LVCMOS clock input).

I am recommending customers to reach out to the Ethernet PL to get the EPHY implementation reviewed but wanted to make some initial recommendations related to the crystal and have the below queries.

For the Crystal is there a recommended series resistor customer should be using for Xi and Xo pins.

Pls Refer below recommendations we provided for the SOC. Is there some similar recommendations that you could share for DP83TC81x and DP83867

Should customers be following the DP83TC81x EVM values (100R and 1K). DP83867 does not use any series resistors.

Regarding the crystal load capacitance, should customer be using 2 X crystal load and does the 2 X crystal load value include PCB capacitance.

Regards,

Sreenivasa

3 months ago

0 Avtar Dhaliwal 3 months ago

TI__Expert 4720 points

Hello Sreenivasa,

I will discuss with my team internally about following the EVM values as well as correct multiplier for crystal load capacitance, and get back to you shortly.

Regards,

Avtar

0 Kallikuppa Sreenivasa 3 months ago in reply to Avtar Dhaliwal

TI__Guru*** 147299 points

Hello Avtar,

Thank you for the note.

While you discuss on the DP83TC81x please note the query also includes the DP83867 and your input for DP83867 along with DP83TC81x is appreciated.

Regards,

Sreenivasa

0 Avtar Dhaliwal 3 months ago in reply to Kallikuppa Sreenivasa

TI__Expert 4720 points

Hello Sreenivasa,

We recommend following the DP83TC81x EVM values for the series resistors on the XI and XO lines.

Furthermore for the DP83867 we recommend following the datasheet which doesnt have any resistance on the XI and XO lines.

Lastly you are correct for crystal load capacitance we recommend the customer use 2 X crystal load.

One more thing to look at is that these parameters also depend on the crystal vendor specs for the crystal as they vary.

Regards,

Avtar

0 Kallikuppa Sreenivasa 3 months ago in reply to Avtar Dhaliwal

TI__Guru*** 147299 points

Hello Avtar,

Thank you.

Kallikuppa Sreenivasa said:
Regarding the crystal load capacitance, should customer be using 2 X crystal load and does the 2 X crystal load value include PCB capacitance.

based on your inputs i understand that the PCB capacitance is not required to be accounted for and the recommendation is to use 2 X crystal load.

Avtar Dhaliwal said:
One more thing to look at is that these parameters also depend on the crystal vendor specs for the crystal as they vary.

Could you please elaborate. the crystal has a specified load and the recommendation is to use load cap of 2 X crystal load.

Is there anything else to consider.

Regards,

Sreenivasa

0 Kallikuppa Sreenivasa 3 months ago in reply to Kallikuppa Sreenivasa

TI__Guru*** 147299 points

Hello Avtar,

Checking if i can use the below app note for DP83867 EPHY?

https://www.ti.com/lit/an/snla290/snla290.pdf?

Regards,

Sreenivasa

0 Avtar Dhaliwal 3 months ago in reply to Kallikuppa Sreenivasa

TI__Expert 4720 points

Hello Sreenivasa,

The 2 X crystal load is a general rule of thumb however for more exact value the equation found in SNLA290 should be used which has PCB capacitance included in Cstray.

And for your second query yes that app note can be used for the DP83867 PHY.

Regards,
Avtar

0 Kallikuppa Sreenivasa 3 months ago in reply to Avtar Dhaliwal

TI__Guru*** 147299 points

Hello Avtar,

Thank you.

Avtar Dhaliwal said:
We recommend following the DP83TC81x EVM values for the series resistors on the XI and XO lines.

I assume this is valid for all the EPHYs. We could follow the EVM configuration for the series resistor values.

If possible please put to gather an FAQ for the crystal load cap and series resistor selection.

Regards,

Sreenivasa

0 Avtar Dhaliwal 3 months ago in reply to Kallikuppa Sreenivasa

TI__Expert 4720 points

Hello Sreenivasa,

Yes that would be recommended.

And yes that would be a good idea, thank you for the feedback.

Regards,
Avtar

0 Kallikuppa Sreenivasa 3 months ago in reply to Avtar Dhaliwal

TI__Guru*** 147299 points

Hello Avtar,

Thank you.

Regards,

Sreenivasa

+1 Avtar Dhaliwal 3 months ago in reply to Kallikuppa Sreenivasa

TI__Expert 4720 points

Hello Sreenivasa,

You are welcome.

Regards,

Avtar

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DP83TC813S-Q1: Crystal Xi and Xo series resistor Value recommendations and Crystal load cap recommendations