Proper automotive design rules - Page 1
Forum section: electronics / projects

author: stef_r
author_rank: Contributor
timestamp: May 14, 2014, 01:01:08 pm
content: Hello,Does anyone know where I could find some good documentation or info about automotive designs?Although it’s for a hobby project, I want to design a circuit that meets the ‘industrial standard’ for automotive applications.The main reason is I want to learn how to design according to professional standards.The circuit is fairly simple:I want to use a PIC with two Smart High Side Switches (Fairchild FDDS10H04A-93242) to drive two positive outputs.On the circuit, I have two inputs. Since I want to build the circuit as it was an commercial automotive application, I had in mind to use two automotive-grade optocouplers (MOC207/8M) for it.Can somebody send me in the right direction on this one?I’m not quite sure how to connect the optocouplers to the ground. (how I create ‘true’ galvanic isolation between the ‘cars’ ground and the ‘digital’ ground of the PIC etc.)Any info about design rules or automotive applications is VERY welcome!

author: tszaboo
author_rank: Super Contributor
timestamp: May 14, 2014, 01:35:57 pm
content: http://www.ixda.org/node/19948I'm sure proper documents describing the rules in lawyerish are available for some hundred dollars each.

author: Scrts
author_rank: Frequent Contributor
timestamp: May 14, 2014, 03:12:31 pm
content: I am working in a huge automotive company and there are so many rules and so many hundreds of pages of documents, that I doubt you'll find them in one place... You have to take into consideration shorted ceramic caps (that's why they have to be used two connected in series and mounted 90 angle on the PCB), also jump stat condition, where your device must not be damaged (or better work without problems) at 28V for 60 seconds (we treat that as infinite). Load-dump, cold-start and many many many more issues... Plus you have to take electrochemical migration into consideration, so many IC packages, that have less than 0.3mm between GND pin/pad and Vbattery are not allowed to use. Sometimes manufacturers like TI take that into consideration and make the packages compatible.

author: DaveW
author_rank: Frequent Contributor
timestamp: May 14, 2014, 03:58:42 pm
content: ISO 7637-2 is a good start for seeing what your power supply should be capable of handling. With some googling it is available on the net

author: max_torque
author_rank: Super Contributor
timestamp: May 14, 2014, 04:56:59 pm
content: Whilst there are no "set" formal rules for a given automotive environment, there are a series of rules that apply to different facets of that environment. Every different manufacturer will specify or use a different set of rules in fact.Broadly these rules fall into the following sections:1) Power supply - things like load dump, reverse battery connection etc2) EMC compliance - ensuring that your device doesn't affect other devices or get effected by them3) Environmental conditions - temp (-30 to 50dgeC usually), humidity, sealing, corrosion, vibration4) Safety critical system design - depend on device, but we are talking about multiple processor error checking, fail safe and diagnostic capabilities here5) Material suitability and recyclability - lead free solders, labeling of plastics etc6) Productionisation and life cycle management - the availability of the components, both now, and for around 10 years has to be guaranteedAnd several more i can't think of at the moment! So in summary, i don't think it's sensible to try to design your device to meet all those rules! Probably just 1) & 3), with as much of 2) as you feel you can do ;-) (assuming your device isn't safety critical itself or effect other devices that are (watch out for devices using vehicles CAN bus, as this can cause safety issues even when nothing to do with that other device etc!)

author: stef_r
author_rank: Contributor
timestamp: May 14, 2014, 06:46:04 pm
content: Thanks for all the answers so far!I've allready red a lot of it.I'm familiar with the load-dump, reverse protection, ESD and EMI issues.at work we have several devices which has been officialy approved to be used in the automotive branche.I also have taken some of them apart to see what's inside and how they managed to solve some issues I'm currently dealing with.Some has only a two-sides PCB with no ground plane (so pretty easy to reverse-engeneering) and some has multi-layer with top and bottom groundplanes.As far as I've learned so far, and from what I've seen with other devices, I came up with this circuit drawing :On top I have a power supply. Load dump and reverse battery protection by the RB040 IC and some filtering through the BNX002 EMI filter.On the bottom I have drawn a input circuit (partly copied from one of the other devices I had taken apart)For the choice of components, I searched specific manufacturers and for specific model ranges to be almost all "automotive-grade".And ofcourse I know I have to take a very close look at the PCB layout because that can make or break everything!Why bother so much about automotive design and regulations since it's 'only' a hobby project?At work, my boss have seen my interests in electronics and electronics designing.If I come up with a good drawing, he is willing to invest in the product and to make it a commercial device.That also means it's going to be tested and approved by 'the officials'.

author: Andreas
author_rank: Super Contributor
timestamp: May 15, 2014, 05:05:41 am
content: Hello,Ford has published some guidelines:http://www.fordemc.com/With best regardsAndreas

author: turbo!
author_rank: Regular Contributor
timestamp: May 15, 2014, 05:42:22 am
content: Automotive use is severe environment.High vibration, splash resistance and extreme temperature and humidity. Rapid and frequent thermal cycling.Even if the component is located in the passenger compartment, it needs to withstand a rapid rise from -30F ish to 200F ish as depending on location the hot heater air can get to it. The ECU needs to stay stable enough for proper functioning without losing gain/offset throughout the entire unit temperature range from being parked at sub zero temperatures to near boiling temperature.If it fogs up on your windshield, it can fog up inside cool electronics too.

author: stef_r
author_rank: Contributor
timestamp: May 15, 2014, 02:03:46 pm
content: Quote from: Andreas on May 15, 2014, 05:05:41 amHi Andreas,Thanks, but I allready came accross this document.There are also some other usefull documents which would help me to document the whole thing.(and there is A LOT of documenting to do)