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TUSB542: AC COUPLING CAP

FRANK1
Expert 8555 points
Part Number: TUSB542
Other Parts Discussed in Thread: TUSB322, TUSB321

Hi sir,

Can I add AC coupling capacitors on SS Rx?

I found thread in E2E mentioned that the AC coupling capacitors on SS Rx is selectable.

what is the condition to add AC coupling capacitors on SS Rx?

and what what is the condition do not add AC coupling capacitors on SS Rx?

what are the respective effects?

BTW, what is value for this capacitor? 330uF or 330nF.

which one is more better?

Thanks.

Regards,

M

  • 0
    TI__Guru 64326 points

    Hi M,.

    SSRX AC coupling capacitance is optional but recommended for most USB 3.1 or lower applications because there should already be AC coupling on the opposing SSTX. Have this capacitance helps to remove any unwanted bias on the SSRX side.

    The value that should be used is 330 nF or 0.33 uF  (There was a typo in that last post) . 

    Note: This capacitance is required as of USB 3.2 spec.

  • 0 in reply to Malik Barton57
    TI__Expert 8555 points

    Thanks a lot.

  • 0 in reply to Malik Barton57
    TI__Expert 8555 points

    Hi Malik,

    For SSRX AC coupling capacitance, I want to use 0.1uF rather than 0.33uF.

    0603 size, and use it in USB 3.1 spec.

    How about the signal quality in two ways of insert 0.1uF cap or not insert 0.1 uF.

    is there any differences?

    will be signal quality turned to better or turned to bad?

    If I do not insert 0.1uF on the side of SSRX, can the signal quality be guaranteed?

    can you give me some suggestion?

    Thx,

    Regards,

    M

  • 0 in reply to FRANK1
    TI__Guru 64326 points

    Hi M,

    You should not use 0.1uF on RX_CON (in between TUSB542 and connector) this will cause DC common mode imbalance on the bus and the total bus capacitance will be too low. 

    In between TUSB542 and the USB Host (or Hub) 0.1uf is okay. See Figure 16. USB-C DRP Implementation Using TUSB542 and TUSB322/TUSB321 in the datasheet and let me know if this does not make sense.