SN65LVCP40: AC-COUPLING CAPACITORS

Nicola Fiorucci

Intellectual 300 points

Part Number: SN65LVCP40
Other Parts Discussed in Thread: DS25CP104A, DS42MB200

Hello,

i need to interface many LVDS input signals to two SN65LVCP40 mux.

All LVDS signals comes from a dedicated connectors.

The outputs of the two SN65LVCP40 (mux) goest to DS25CP104A (cross-point) and finally to an LVDS connector.

I need to know where i need to place ac-coupled capacitos in the paths. For sure i'm going to place ac capacitors after the input connectors (mux inputs) but i don't know if they are required to place at the output of the SN65LVCP40 (between mux and cross-point) and at the output of the DS25CP104A (cross-point).

Thanks

over 7 years ago

0 Lee Sledjeski over 7 years ago

TI__Mastermind 43795 points

Hi,

If you can substitute the DS42MB200 for the SN65LVCP40, it is possible to avoid using AC coupling capacitors on the DS25CP104A input side. If the device receiving the signals on the output of the DS25CP104A is compatible to the LVDS standard, there should be no need for AC coupling capacitors in this location either.

Regards,

Lee

0 Nicola Fiorucci over 7 years ago in reply to Lee Sledjeski

Intellectual 300 points

Thanks. Unfortunately i can't replace the SN65LVCP40. This is how i would like to implement the LVDS out.

0 Lee Sledjeski over 7 years ago in reply to Nicola Fiorucci

TI__Mastermind 43795 points

Hi Nicola,

I have used AC coupling capacitors on the DS25CP104A like this before. You may not need the coupling capacitors on the output as the CP104A outputs are 100% compatible with LVDS inputs.

Regards,

Lee

0 Nicola Fiorucci over 7 years ago in reply to Lee Sledjeski

Intellectual 300 points

My doubt is if i need to place capacitors between SN65 and DS25

0 Lee Sledjeski over 7 years ago in reply to Nicola Fiorucci

TI__Mastermind 43795 points

Yes, the 1.65V common mode voltage is close to an internal trip point in the DS25CP104A receiver. If the common mode is at exactly the wrong voltage, it can result in bit errors on the DS25CP104A output.

0 Nicola Fiorucci over 7 years ago in reply to Lee Sledjeski

Intellectual 300 points

Thanks very much.

I will put AC-coupling capacitors between SN65 and DS25.

Where is the best position of this capactitors? Is it near driver (SN65) or near receiver (DS25)?

Thanks

Best Regards

Nick

0 Lee Sledjeski over 7 years ago in reply to Nicola Fiorucci

TI__Mastermind 43795 points

Hi Nick,

I usually try to place them closer to the receiver. This gives the transmitted signal edge rates a little time to slow down minimizing any chance that the capacitor will result in some signal reflections on the transmission line.

Regards,

Lee

0 Nicola Fiorucci over 7 years ago in reply to Lee Sledjeski

Intellectual 300 points

Thanks Lee,

i have anther question.

I need to place more DS25 to make a bigger multiplexing on LVDS signal.

Do i need to place AC-capacitors even between DS25?

Thanks

0 Lee Sledjeski over 7 years ago in reply to Nicola Fiorucci

TI__Mastermind 43795 points

Hi Nicola,

There is not a requirement to place AC capacitors between DS25 devices.

Regards,

Lee

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SN65LVCP40: AC-COUPLING CAPACITORS