DP83620 AC coupled?

Calum Mackinnon

Other Parts Discussed in Thread: DP83620

Hi,

This is not necessesarily a DP83620 issue its more advice I am after.

I’m designing a MAC-PHY device using the Avago fiber transceiver HFBR-5963LZ/ALZ. On the datasheet of the part it says the pins are PECL compatible and it only shows how to connect the PHY to MAC in DC topology (fig 3, 4 on datasheet).

I Just noticed that the PHY I’m using DP83620, TI recommends AC coupling although it also supports PECL signaling. I’m a bit concerned because I used the schematic on fig 3 of the HFBR-5963LZ data sheet as my reference design (which is not AC coupled) whereas TI recommends AC coupling (pg 35 of datasheet).

Do you see an issue if I add a 0.1uF AC couling cap betweem the the Phy and the Transceiver? Or can I get away with no cap(I already have my design well through layout!!)

Thanks for any help you can offer.

Calum

over 13 years ago

0 Avi Chami1 over 13 years ago

Mastermind 7395 points

In case of doubt, and since you are under time constraints... I would put the AC coupling capacitor. You can always replace it with a 0 Ohm resistor later, but if you really need it and there is no place to fit it... that is real trouble.

0 Patrick OFarrell over 13 years ago in reply to Avi Chami1

TI__Mastermind 31600 points

The Avago datasheet shows a DC connection to the fiber transceiver, but it also shows an LVPECL driver in the Phy. The DP83620 driver is not an LVPECL driver. Therefore, the connection from the DP83620 to the Avago fiber transceiver should be AC coupled.

Also note that there are differences between the signal detect levels for the devices. The Avago HFBR-5963LZ/ALZ signal detect uses LVTTL levels. The DP83620 signal detect expects LVPECL levels. This difference in signal levels must be accounted for as well.

Patrick

0 Calum Mackinnon over 13 years ago in reply to Patrick OFarrell

Genius 4155 points

Thanks Patrick,

Is there an IBIS model I can get?

Cheers

Calum

0 Patrick OFarrell over 13 years ago in reply to Calum Mackinnon

TI__Mastermind 31600 points

Calum,

There is an IBIS model available for the DP83620, but it only models the digital I/O pins. The fiber interface is not modeled.

For reference, the direct link for the IBIS model is:

http://www.national.com/assets/en/tools/ibis/dp83620.ibs

Patrick

Interface

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DP83620 AC coupled?