topic Re: SC18IM700 TX-Line Driving Issues in Other NXP Products

SC18IM700 TX-Line Driving Issues

benjaminwyrsch — Wed, 03 Jan 2018 13:19:17 GMT

We are using the SC18IM700 in our design.

We have detected that the TX-line shows some artifacts during the rising and the falling slope.

What is the reason for these artifacts?

Is the output driver that weak?

There is an external 10kOhm pull-up resistor in the TX-line.

I don't think that this resistor causes the artifacts.

I also couldn't find any electrical specification of the TX-line output in the datasheet.

Can anybody provide the electrical specification and detailed information about the electrical output circuit (open-drain, push-pull, etc)?

Thanks

Benjamin

Re: SC18IM700 TX-Line Driving Issues

david_diaz — Mon, 08 Jan 2018 18:36:53 GMT

Hello Benjamin,

The pull-up at the TX line could slightly prolong the signal’s fall time. Have you considered to remove or decrease the pull-up resistor?

If you remove the resistor, does the signal behave correctly? Could you please share your results?

Regards,

David

Re: SC18IM700 TX-Line Driving Issues

benjaminwyrsch — Thu, 15 Feb 2018 08:34:59 GMT

We have found the reason for the artifacts: We were using a bidirectional level-shifter IC for the TX and RX lines. This level shifter doesn't work properly with slow slopes resp. open-drain circuits. We have replaced this IC with direction controlled buffers. All is good now.