Steffen, It has been my experience that when unique ID's must be placed on backplanes, it is usually desirable to make them difficult to alter in the field. Any kind of field replaceable assy defeats that, whereas, the Si ID devices, be they LASER ID's or a combination of LASER ID and EEPROM do a decent job of enforcing that. I have found that most houses recommend hand soldering as there are very few connections and it just doesn't make sense to try and reflow a big press-fit assy. I did work with one company who put their device in as an afterthought, and consequently had not worked out the power issue. It is pretty simple to supply OR'd LV power using a series diode and either a series ballast resistor, or active current source ( my preference ) from each of N redundant daughter cards. A three terminal series or shunt regulator, ( I personally prefer shunts for this ), is then placed at the ID device. Only the ID device and its regulator need to be on the BP, so no more than two SO-8's. It's a good idea to work out fabrication w/ your BP assy house before committing placement. Regards, Steve. At 09:32 AM 10/17/2003 -0700, Steffen Hagene wrote: >Placing an EEPROM on a backplane does not make it active in the strict sense >as the active components are not part of the signaling path (driver, >termination, etc.). It is best to avoid active components on backplanes in >general, although sometimes the system design will require it. There are a >couple of reasons why you don't want to do this. The first is that it >completely changes the manufacturing process of the backplane. What was a >press-fit only assembly now has to go through a soldering process and its >associated thermal excursions. Backplanes are typically a lot thicker and >larger than other fabs and they are affected differently when heated than a >typical daughterboard. A lot of assembly shops have limits on the size of >the assembly that they can solder as well. The other issue is that the >system power distribution scheme is altered. Telecom systems typically >distribute 48 volts and regulate locally on each FRU. An active backplane >will now require distribution of a regulated supply across the interface. >You have to ensure that this power is clean and of the appropriate level. > >Keep in mind that a passive backplane does not require an EEPROM per the >standards as an active FRU does. Putting one on an otherwise passive >backplane greatly increases your problems. If you need a unique ID on a >backplane you are a lot better off using a programmable shunt in a socket >which can be read by the controller. > >Steffen Hagene >Engineering Manager >PalPilot Corporation > > > > -----Original Message----- > > >From: "Naveen Reddy" <naveenr@xxxxxxxxxxxxxxx> >Subject: [SI-LIST] Active components on a highspeed backplane >Date: Thu, 16 Oct 2003 11:52:32 -0700 > >Dear All, > >Have any of you folks had any designs where you had to place an active >component on the backplane? In particular, I need to have a unique >'Board ID' for each backplane and the only feasible solution I can think >of is to add a Serial EEPROM; but I am a little weary of this solution >because of the risk of 'frying' the chip. > >Using dedicated pins on connnectors is another possibility, but this is >going to require more pins than I can spare. If you have had designs >similar to this, I would really like to hear your thoughts on this. > >Regards >Naveen. > > > > > > > >------------------------------------------------------------------ >To unsubscribe from si-list: >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >or to administer your membership from a web page, go to: >//www.freelists.org/webpage/si-list > >For help: >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >List archives are viewable at: > //www.freelists.org/archives/si-list >or at our remote archives: > http://groups.yahoo.com/group/si-list/messages >Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu