DP83867IR: DP83867IR connection question

Hello Roy, 

A 25M crystal can be used for all speed and interface applications.

Regarding the second question, i am having difficulty understanding the question. What do you mean by clock sync for MDIO ?

MDIO needs a pullup and MDC does not need to be pulled up while using.

If not used, it would be a good idea to terminate depending on he product EMC requirement.

Do remember they have weak pull down resistors.

Regards,

Sreenivasa

Hi Screeivasa,

Is it ok to use below structure? If it's ok, can you let me know the spec need of OSC?

Roy

Hello Roy, 

hank you for the query.

You can use this way or use the clock out of the PHY1 for running PHY2.

The requirements would be similar to the crystal requirements in the datasheet.

What is the IO voltage you are considering ?

Regards,

Sreenivasa

Hello Roy,

Do you have some inputs. Please note the IO voltage is higher than 1.8V, a capacitor divider has to be used to divide the clock input.

If you do not have any additional questions, i will close the thread.

Regards,

Sreenivasa

Hi Sreenivasa,

Thanks for note. We used 3.3V and so we need to follow below circuit. Is it correct?

Roy

Hello Roy,

Thank you for he inputs and this is correct.

Regards,

Sreenivasa

Hi Sreenivasa,

Can you let me know if we use four DP83867, is below structure ok?

Roy

Hello Roy,

This architecture may have challenges since the Xo driven by the crystal may be limited by its drive capability.

Any thoughts on the use case for this architecture ?

Regards,

Sreenivasa

Hi Sreenivasa,

Customer use use 4 PHYs in their system. I can tell them use one OSC for two DP83867 is our suggestion.

In addition, in power sequence, I only see 2.5V and 1.8V, but we only have 3.3V/2.5V/1V, do I need to follow any power sequence?

Currently, our power sequence is 1V -> 2.5V -> 3.3V

Roy

Hello Roy, 

They can use a common oscillator + buffer or one OSC for two DP83867 as you suggest.

For the two supply operation, there is no requirement for power sequencing. 

Please note that the supply ramp of >500us has to be ensured.

Regards,

Sreenivasa

Hi Sreenivasa,

I'm not sure the meaning of below. do you mean rise time > 500us?

Kallikuppa Sreenivasa said:

Please note that the supply ramp of >500us has to be ensured.

Roy

Hello Roy, 

Yes that is correct,

Regards,

Sreenivasa

Hi Sreenivasa,

May you let me know why should >500us because I only saw the rise time should < specific value. First time to see '>'

Roy

Hello Roy, 

You are right, there is a max ramp time which is specified.

There is also a minimum supply ramp time. I am providing the table from the DP83869 for your reference.

If the ramp time is faster, there is a possibility of the internal ESD diodes being triggered that can result in higher power consumption.

Regards,

Sreenivasa

Hello Roy, 

If you do not have additional question , can you please click the resolved button to close.

Regards,

Sreenivasa