Timeline for Long transmission line inductance with SPI
Current License: CC BY-SA 3.0
20 events
when toggle format | what | by | license | comment | |
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Jul 28, 2012 at 3:24 | answer | added | Chris Stratton | timeline score: 4 | |
Jul 27, 2012 at 20:45 | comment | added | The Photon | @Peter, my first thought was "he can probably use a snubber"... but then I realized you'd given so little information and some things were non-physical as described so I didn't feel safe giving that answer...For future questions, please try to give us some help to help you, and you'll be more likely to get a good answer in a shorter time. | |
Jul 27, 2012 at 20:15 | comment | added | markrages | Can you take a picture of your scope probe connected to the circuit? | |
Jul 27, 2012 at 19:59 | vote | accept | Peter | ||
Jul 27, 2012 at 19:59 | answer | added | Peter | timeline score: 2 | |
Jul 27, 2012 at 19:42 | comment | added | Peter | @ThePhoton I can't open up the cable and there is no documentation on it. I am assuming it is a 26AWG wire bundle. Definitely not coax or ribbon. | |
Jul 27, 2012 at 19:42 | comment | added | Peter | @stevenvh I will post a few pics. I thought about it last night and I have a 'good enough' solution at the moment, but I'd like to understand the underlying issue. | |
Jul 26, 2012 at 5:52 | comment | added | stevenvh | I don't expect a higher RC will be the solution, I just want to see what's needed to get some effect. (service message: I like "Steven" better than "@stevenvh", but you'll have to write the latter, otherwise I won't get notified of your comment. I don't have to write "@Peter" because you'll get notified anyway since it's your question.) | |
Jul 25, 2012 at 19:56 | comment | added | Oli Glaser | How many SPI ICs are there on the board side? Have you tested to see if the spikes are present on the PCI side without the cable/board connected? Have you tried just using a series resistance rather than the RC filter? (i.e. no C) Also answering Photon's questions would definitely help to get to the bottom of this. | |
Jul 25, 2012 at 18:44 | comment | added | Nick Alexeev | app note on the subject: Extending the SPI bus for long-distance communication. | |
Jul 25, 2012 at 16:47 | comment | added | Saad | You could add resistor and two schottkys at the receiver. The schottky will clip the voltage at Vcc+Vf - where Vf is the forward voltage drop of the diode. | |
Jul 25, 2012 at 16:35 | history | tweeted | twitter.com/#!/StackElectronix/status/228166653924478977 | ||
Jul 25, 2012 at 16:29 | comment | added | Peter | Steven: I have not and that is something I was planning on looking at next, but I don't think that will be the final solution. It surprised me that I saw no noticeable drop in spike when I put the RC in. I approximated 40nS spike as equal to 25Mhz (1/40ns) so I would have expected at least a 20dB drop. I am now speculating that perhaps inductance in the return line is mitigating the capacitor? That's why I was thinking of just sticking at IC buffer/zener on the lines. But that seems like a bazooka to kill a fly approach. ;) | |
Jul 25, 2012 at 16:19 | comment | added | The Photon | Is the cable ribbon cable? coax? twisted-pair? What are the wire sizes? Does it have equal number of signal and ground wires? What's the arrangement of signal relative to ground wires? When you observed the 12 V overshoot, how and where were you probing your circuit? What was the duration of the overshoot? Was there equal undershoot on falling edges? Can you post a schematic of your receiving circuit? | |
Jul 25, 2012 at 16:15 | comment | added | The Photon | Something is fishy here. If you just had a transmission line mismatch, you could not have more than 100% overshoot. It would be good to understand the root cause of the problem before trying to suggest an answer. Could you post a photo of the system to make clear the construction of the boards, cables, etc.? A scope trace of the overshoot signal? | |
Jul 25, 2012 at 15:36 | comment | added | stevenvh | Peter, have you tried higher values for the RC than 100 ohm, 1 nF? At 800 kHz it may distort your pulses, and maybe give receive errors, but I would like to know how it affects the overshoot. How about 1 kohm and 10 nF? | |
Jul 25, 2012 at 14:50 | comment | added | stevenvh | @clabacchio - I should think so. 12 V on a 5 V supply is 140 % overshoot. | |
Jul 25, 2012 at 14:43 | answer | added | Andrejs Cainikovs | timeline score: 0 | |
Jul 25, 2012 at 14:34 | comment | added | clabacchio | Do you have a specific issue with the spikes? | |
Jul 25, 2012 at 14:16 | history | asked | Peter | CC BY-SA 3.0 |