PCB connector pinout - crosstalk - Page 1
Forum section: electronics / projects

author: sirwin
author_rank: Newbie
timestamp: June 19, 2015, 05:57:48 pm
content: Hi all,I have a PCB I'm designing that has a 2x6 connector with multiple digital signals and power supplies going through. The digital signals are SENT protocol (see SAE J2716). There are two independent power supplies at 5V. I plan to have decoupling capacitors on each power supply to it's respective ground.What are some guidelines I can apply to reduce the potential crosstalk between the different pins?Here is my connector schematic. The pinout is probably not optimized.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 19, 2015, 06:27:51 pm
content: We don't know what "2x6 connector" you are talking about.But it seems likely that any potential crosstalk symptoms will be much more strongly influenced by the cabling than by a single connector.

author: lapm
author_rank: Frequent Contributor
timestamp: June 19, 2015, 08:12:16 pm
content: https://en.wikipedia.org/wiki/SENT_(protocol)After quick look at this, i would recommend classic method.. Shielded cable per signal, or ribbon cable with every other wire as common ground.

author: Andreas
author_rank: Super Contributor
timestamp: June 19, 2015, 09:08:49 pm
content: Quote from: lapm on June 19, 2015, 08:12:16 pmReally?The edges of SENT are EMI-optimized (relatively slow).If the lines do not run very long in parallel there will be no significant cross talk.(and at the receiver the filter capacitor will filter out the rest).If you want to optimize it anyway and are fixed to the 12 pin connector:it is sufficient to place one power line after 2 signal pins. (either 5V or gnd).In this case I would distribute the power lines symmetrically between the signal lines.With best regardsAndreas

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 19, 2015, 09:11:21 pm
content: It's not apparent if this is a high speed, impedance controlled system or a low speed, slew rate limited system (i.e., some proprietary version of UART over some proprietary version of RS-232).Do you have datasheets for the drivers?What type of connector is that? Regular pin header? Something else?Tim

author: tggzzz
author_rank: Super Contributor
timestamp: June 19, 2015, 09:12:07 pm
content: Why not have the PSU on pint 2,5,8,11?

author: ConKbot
author_rank: Super Contributor
timestamp: June 19, 2015, 10:05:28 pm
content: Since the protocol is asynchronous, and assuming it's no more speedy than rs 232, then the nibble should be static while it's being read, so cross talk between bits shouldn't be to bad, so, just isolating the different channels (assuming thats an rx and a tx there. If you're using a 0.1" header to ribbon cable, then you're first pinout really needs changing. If not then it's probably fine.But asT3sl4co1l said, it depends on a lot of things. The absolute safest bet would be to use a shielded ribbon cable and pin it so there is a ground between each signal (or power, as if it is properly decoupled, they are both low impedance)

author: Andreas
author_rank: Super Contributor
timestamp: June 19, 2015, 10:17:38 pm
content: Quote from: T3sl4co1l on June 19, 2015, 09:11:21 pmHello,one example of a "driver" is the TLE4998Shttps://www.infineon.com/dgdl/Infineon-TLE4998S-DS-v01_00-en.pdf?fileId=db3a30431ce5fb52011d3ec7bd4c25bdThe fall time (the faster edge) is between 2-4 us -> slooow.It has nothing to do with RS-232. The information is coded into the distances of the falling edges. (4 bits at one time/edge).With best regardsAndreas

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 20, 2015, 12:33:56 am
content: Yeah, looks pretty slow. Maybe some concern with crosstalk or interference during the high impedance (pull up / open circuit) rises? If the receiver has filtering and stuff, that might not matter anyway.Tim

author: sirwin
author_rank: Newbie
timestamp: June 20, 2015, 11:10:51 pm
content: Thanks for the replies guys.I do not have influence over the type of cabling to the receiver. I can only specify a pin out. It is a regular 0.1" pin header on the board.I also have no information on any filtering done by the receiver.I can't give a datasheet on the driver as it is not released and I'm under a NDA. It is very similar to the Infineon TLE4998 that Andreas linked.It looks like my best bet is to intersperse the signals among the supplies and grounds.

author: Andreas
author_rank: Super Contributor
timestamp: June 21, 2015, 09:45:45 am
content: Quote from: sirwin on June 20, 2015, 11:10:51 pmfor a regular pin header the counting of the pins is unusual.Usually the pins are counted in the order of the wires which are connected.1 = red wire first row2 = next wire = first pin on other row of connector (where you have pin 12)3 = 2nd pin of first row.With best regardsAndreas

author: sirwin
author_rank: Newbie
timestamp: June 22, 2015, 01:21:51 pm
content: Quote from: Andreas on June 21, 2015, 09:45:45 amThat's just how the mating connector pins are numbered. I matched the header numbers to that connector.