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Original question:

SN65LVCP114: SN65LVCP114 has AC coupling in RX?

SN65LVCP114: High speed IO ac-coupling capacitor recommendation

roya azimi
Intellectual 725 points
Part Number: SN65LVCP114

Hi TI,

In SN65LVCP114 EVM, used from 0.1uF 0201 capacitors for ac-coupling in RX/TX.

question 1: is there any recommendation for ac-coupling capacitors footprint in RX/TX? for example is it OK to use 0.1uF 0402 capacitor?

question2: is there any recommendation for ac-coupling capacitor side?(it should be closer to receive side or transmit side?)

Thanks.

  • 0
    TI__Guru* 93670 points

    Hi Roya,

    1). 0.1uF O402 form factor capacitor size is fine. Normally it is preferred to have the pad size to be the same as trace width as much as possible. This way there is less impedance mis-match. Also, we normally use void(no ground or VCC) under AC coupling caps. This will reduce parasitic and thus impedance drop due to this parasitic.

    2). Some specification such as PCIe requires AC coupling caps on TX side.  It is recommended to put the AC coupling Cap between TX pin and the connector(> 1 inch from device pin). This will dissipate TX pin reflected energy due to the impedance mis-match.

    Regards,, Nasser