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TUSB1002A: AC Caps

Sepeedah Zadeh
Expert 3100 points
Part Number: TUSB1002A

Hello team, 

My customer is designing with TUSB1002A and we have a few questions regarding AC caps:

  1. In datasheet section 6.5 there is a defined maximum AC coupling capacitance of 265nF. What are the consequences of exceeding this value? Customer host recommendation is the placement of 330nF capacitors along the TXP2/TXN2 pair and 220nF capacitors along the RXP1/RXN1 pair. I think the RX1 is fine, not sure about TX2 however.
  2. Also, hhould the capacitance on either side match? For example, should the AC coupling capacitance on RXP1 and TXP1 be the same? What would be the consequences of a mismatch in capacitance?

 

  • 0
    TI__Guru 64326 points

    Hi Sepeedah,

    1. Is this a Type-C application? Typically TX pair should have 220 nF and RX pair should have 330 nF (optional but recommended) from the re-driver to the connector. For Type-A/B application TX is AC coupled with 100 nF and RX pair has 330 nF (optional). One consequence  of exceeding the spec can cause DC common mode violations for LFPS at device insertion.

    2. Not necessarily, all USB3 transmitters are AC coupled so for internal connections they would match but when AC coupling to the connector they will not match. You are refer to Figure 18. Host Implementation Schematic in the datasheet for a example.