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HD3SS460: HD3SS460 : AC Coupling CAP

user3810803
Prodigy 80 points
Part Number:

Please refer the Figure3 of HD3SS460's datasheet as below :


 
The block diagram shows the AC coupling CAP just be implemented on both TX1+/- and TX2+/- near USB TypeC side ,
so please help to confirm how to process the connection of both ML0+/- and ML3+/- between HD3SS460 and DP_source ? (Does it also need any AC coupling CAP?)

And if we've change the design as below , does it have any risk ?

  • 0
    Prodigy 80 points

    user3810803 said:

    Part Number: HD3SS460

    Please refer the Figure3 of HD3SS460's datasheet as below :


     
    The block diagram shows the AC coupling CAP just be implemented on both TX1+/- and TX2+/- near USB TypeC side ,
    so please help to confirm how to process the connection of both ML0+/- and ML3+/- between HD3SS460 and DP_source ? (Does it also need any AC coupling CAP?)

    And if we've change the design as below , does it have any risk ?

  • 0 in reply to user3810803
    TI__Guru 64326 points

    HD3SS460 contains passive switches which need to be biased DC biased on either the source or connector side.

    We suggest not putting AC coupling capacitors on the Source side so the DC bias can be controlled by the DP source which normally haves less variability than the connector side.  

    The design in the second image would allow the HD3SS460 to be DC biased by any device connected which could result in signals passing through having too high or too low of a DC bias. 

  • 0 in reply to Malik Barton57
    Prodigy 80 points
    Hi ,
    I've find out the POST : e2e.ti.com/.../565369 indicates HD3SS460 is a simple passive switch .
    And I think the design follow the typcial design (Figure 3) still have AC coupling CAP on both ML0+/- and ML3+/- near DP source side .
    Maybe the DC biased is not controllable voltage for HD3SS460 inside , so I just want to make sure the second image design is working normally , or not ?

    P.S. : We have design the CPU_On_Module such as QSEVEN/COM_EXPRESS in our backplane, and CPU_Module have AC Coupling CAP already (Follow the design guideline) .
    So if our Backplane also follow HD3SS460's typical design , it will cause the twice AC Coupling CAP on both TX1+/- and TX2+/- .

    Thanks .
  • 0 in reply to user3810803
    TI__Guru 64326 points
    HD3SS460 does need a external DC bias from either the source or connector side. If I understand correctly, in the second image there would be AC coupling capacitors on all relevant pins. This will disrupt the functionality of the HD3SS460, at least one side on the device needs to be DC coupled. In this case having the DP source DC coupled is still suggested.
  • 0 in reply to user3810803
    TI__Guru 60870 points
    Why would the design have twice the AC coupling caps on the TX pairs? TX1+/- and TX2+/- should be routed to the Type C connector.

    You can check out this reference design to see how the HD3SS460 is used in a real world application:

    www.ti.com/.../sllu248b.pdf


    Regards,
    JMMN