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DS90C241: Unable to decide whether to keep digital ground isolated or shared

Deepak Kukreja
Prodigy 30 points
Part Number: DS90C241
Other Parts Discussed in Thread: DS90C124

Hi,

I am planning to use the Serdes pair DS90c124 and DS90c241 in a design.

I use the serializer to serialize 24 signals (max frequency signal 10 MHz) and send them across a 5 meter CAT5e cable to the Auxiliary board.

The boards are powered by separate 24V SMPS.

I need your help to understand whether the "24V Digital Ground" should be made common between the two boards or kept isolated.

Since the only interface between these 2 boards is the differential pair, I feel this must not be required.

ON my research on the internet, I have seen some people suggesting isolating the two power supplies, and some people suggest that making the ground common is not required.

Please suggest.

  • 0
    TI__Intellectual 1450 points

    Hi Deepak,

    Do you mind telling me your application? I am a little bit confused on if you are trying to put the serializer and deserializer on the same board or separate boards. If on separate boards (this is the normal application) the digital grounds should be kept isolated between the two boards. I am attaching the datasheet below where on pages 23 and 24 it shows the digital grounds of the serializer and deserializer kept isolated to the specific boards.

    I believe this might answer your if I am understanding it correctly. Please let me know if not.

    https://www.ti.com/lit/ds/symlink/ds90c124.pdf?ts=1657139551869&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FDS90C124 - Datasheet

    Best regards,

    Anthony

  • 0 in reply to Anthony Goldhawk
    Prodigy 30 points

    Hi Anthony,

    Thanks for the reply.

    In my application the serializer and the deserializer are on separate boards separated connected using 5 meter CAT5e cable.

    Both the boards have their own separate power supply. 

    In this setup I was thinking if I need to make the DC_GND of both the power supplies common.

    The pages you mentioned in the data sheet do show separate boards, but do not mention whether they are powered by separate supplies or not.

    With regards

    Deepak

  • 0 in reply to Deepak Kukreja
    TI__Intellectual 1450 points

    Hi Deepak,

    If you know that you can send PoE (power over ethernet) using the cat5e cable then you only need one power supply. If PoE can be sent over the cat5e cable I would recommend testing the power being sent over the cable to make sure that the second board has enough power to function properly. If PoE cannot be sent over the cat5e cable then you will need two power supplies. Similarly, if the PoE being sent over the cat5e cable does not supply enough power to allow the second board to function properly then two power supplies will be needed for your application.

    If one power supply is being used then a common digital ground would make sense. On the contrary, if two power supplies are being used then keeping the digital grounds isolated is what I would recommend.

    I hope this helps to answer your question.

    Best regards,

    Anthony