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From: Jim Thompson on 22 Nov 2009 17:20 On Sun, 22 Nov 2009 14:10:29 -0800, Joerg <invalid(a)invalid.invalid> wrote: >krw wrote: >> On Sun, 22 Nov 2009 13:32:09 -0800, Joerg <invalid(a)invalid.invalid> >> wrote: [snip] >>> In one of my recent cases the crowbar was put in there because the board >>> could otherwise take out a $10k laser connected to it. Now that would >>> really make for a pissed client. Not so much because of the $10k but >>> because it would take more than a month of leadtime to get a new one. >> >> A false trip on the crowbar has the same effect for us. Show doesn't >> go on, customer mad as hell. He doesn't much care if it was $1 or >> $10000s of electronics smoking. It's not working. >> > >Mine are working. I've yet to see a false trip of one of my crowbar >designs and it's been >>20 years now. > > >>> It's like the airbag in a car. After it has opened you cannot continue >>> to drive and it'll be an expensive repair bill but it may have saved a >>> lot of grief. >> >> If it went off when there was no accident, you still have at least >> second degree burns, broken arms and thumbs, and perhaps no ear drums. >> ...and haven't saved a damned thing. >> > >But they rarely go off without an accident. You need to exceed >life-threatening G-forces to make the sensor signal an accident. > > >> See, I can burn strawmen too. ;-) > >:-) Yep, Joerg, Sometimes _even_ _you_ can toss out strawmen and be aggravating ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 |
From: Greg Neff on 23 Nov 2009 12:06 On Fri, 20 Nov 2009 18:05:07 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: <snip first post> > >I'm thinking that it would be prudent to clamp or crowbar all the >supplies so that silly regulator problems don't take out expensive >chips. Transzorbs don't work at low voltages, and real SCR crowbars >would be a PITA. > >I was thinking about a string of power diodes > > > > +---- +3.3 > | > | > --- > \ / > --- > | > +---- +2.5 > | > | > --- > \ / > --- > | > + > | > | > --- > \ / > --- > | > | |/| > +--------------| |----- +1.8 > | |\| > +---- +1.5 > | > | > --- > \ / > --- > | > +---- +1.2 > | > | > --- > \ / > --- > | > + > | > | > --- > \ / > --- > | > gnd > > >using something like S3DB's and maybe some strategically-placed >schottkies. > >One can also make a pseudo-zener from a bandgap and a bipolar power >transistor, which would take more parts but be more accurate. > >Or maybe really crowbar the 3.3 volt rail with an SCR that's fired if >any of the switchers go nuts. > >John > > We did a similar, but bidirectional, diode clamp arrangement on a PowerQUICC SBC. Everything worked fine in the lab and in production test, but the customer reported some cases of the SBCs not starting up. In our case the customer supplied a 5V rail, and we used TI TPS54610 switchers to provide 3.3V and 2.0V. We found that the customer 5V startup was much faster than our lab and production power supplies. One TPS54610 started quickly, pulling up the output of the other via one of these diodes, which confused it and prevented it from starting. We had to adjust the soft-start capacitor values to ensure that the switchers started in the correct order, so that they didn't get confused by their outputs being pulled up via the clamp diodes during startup. ================================ Greg Neff VP Engineering *Microsym* Computers Inc. greg(a)guesswhichwordgoeshere.com
From: John Larkin on 23 Nov 2009 18:21 On Fri, 20 Nov 2009 16:22:15 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >OK, I just got the first board from production this morning, for this >spectroscopy controller thing. > >ftp://jjlarkin.lmi.net/First.JPG > >It gets 12 volts in, which runs an LTM8023 switcher brick to make 3.3 >volts. The 3.3 runs most of the logic on the board (including a >Spartan 6 and a PLX PCIe bridge, both BGAs) and also drives four >secondary switchers and some LDOs to make 1.2, 1.5, 1.8, 2.5, and -5 >for various uses. > >So when I powered it up everything went nuts. The PLX chip was >obviously fried. After that was pulled, the Xilinx was running hot, >and the 3.3 volt supply was bogged down to about 2.6. The LTM >regulator was hot. > >Pulled the Spartan BGA next. > >Now the 3.3 volt rail wants to run at 5 or so. > >After much head scratching, I discovered this: > >ftp://jjlarkin.lmi.net/Swapped.jpg > >The resistor that's screened "R127" is actually R129. And vice versa. >So the switcher was programmed wrong, told to run at an absurdly low >frequency and an absurdly high voltage. The ref designators somehow >got misplaced during layout. We usually check for this. > >Apparently our production people, when semi-auto placing dense parts, >double-check the ref designator and plop the part into the "correct" >place, even if the machine coordinates are a little off. I'll have to >warn them to be suspicious about cases like this, especially on first >articles. > >TGIF > >John > > OK, we fixed the power supply and replaced both BGA chips. ftp://jjlarkin.lmi.net/First_Light.jpg On the aluminum plate is the Kontron SBC, running Linux. It connects to our controller board through the short silver PCI Express jumper cable. So far, it's powered up, things look reasonable, and we have Linux talking to the PCIe chip. Next step is to get the FPGA configured and doing stuff. The NewHaven LCD looks real nice. The Kontron is talking to it RS-232, with a little AVR processor on the user interface board handling the LCD and buttons and LEDs. John
From: JosephKK on 28 Nov 2009 06:57 On Sat, 21 Nov 2009 18:59:49 +0000, Raveninghorde <raveninghorde(a)invalid> wrote: >On Fri, 20 Nov 2009 16:22:15 -0800, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>OK, I just got the first board from production this morning, for this >>spectroscopy controller thing. >> >>ftp://jjlarkin.lmi.net/First.JPG >> >>It gets 12 volts in, which runs an LTM8023 switcher brick to make 3.3 >>volts. The 3.3 runs most of the logic on the board (including a >>Spartan 6 and a PLX PCIe bridge, both BGAs) and also drives four >>secondary switchers and some LDOs to make 1.2, 1.5, 1.8, 2.5, and -5 >>for various uses. >> >>So when I powered it up everything went nuts. The PLX chip was >>obviously fried. After that was pulled, the Xilinx was running hot, >>and the 3.3 volt supply was bogged down to about 2.6. The LTM >>regulator was hot. >> >>Pulled the Spartan BGA next. >> >>Now the 3.3 volt rail wants to run at 5 or so. >> >>After much head scratching, I discovered this: >> >>ftp://jjlarkin.lmi.net/Swapped.jpg >> >>The resistor that's screened "R127" is actually R129. And vice versa. >>So the switcher was programmed wrong, told to run at an absurdly low >>frequency and an absurdly high voltage. The ref designators somehow >>got misplaced during layout. We usually check for this. >> >>Apparently our production people, when semi-auto placing dense parts, >>double-check the ref designator and plop the part into the "correct" >>place, even if the machine coordinates are a little off. I'll have to >>warn them to be suspicious about cases like this, especially on first >>articles. >> >>TGIF >> >>John >> >> > >Experience has taught me to power up new boards on a bench psu by >winding up the voltage from zero while monitoring the supply rails and >input current. Do all the testing you see fit. This case can be used to argue for "hard start" testing.
From: JosephKK on 28 Nov 2009 07:35
On Sun, 22 Nov 2009 15:20:30 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Sun, 22 Nov 2009 14:10:29 -0800, Joerg <invalid(a)invalid.invalid> >wrote: > >>krw wrote: >>> On Sun, 22 Nov 2009 13:32:09 -0800, Joerg <invalid(a)invalid.invalid> >>> wrote: >[snip] >>>> In one of my recent cases the crowbar was put in there because the board >>>> could otherwise take out a $10k laser connected to it. Now that would >>>> really make for a pissed client. Not so much because of the $10k but >>>> because it would take more than a month of leadtime to get a new one. >>> >>> A false trip on the crowbar has the same effect for us. Show doesn't >>> go on, customer mad as hell. He doesn't much care if it was $1 or >>> $10000s of electronics smoking. It's not working. >>> >> >>Mine are working. I've yet to see a false trip of one of my crowbar >>designs and it's been >>20 years now. >> >> >>>> It's like the airbag in a car. After it has opened you cannot continue >>>> to drive and it'll be an expensive repair bill but it may have saved a >>>> lot of grief. >>> >>> If it went off when there was no accident, you still have at least >>> second degree burns, broken arms and thumbs, and perhaps no ear drums. >>> ...and haven't saved a damned thing. >>> >> >>But they rarely go off without an accident. You need to exceed >>life-threatening G-forces to make the sensor signal an accident. >> >> >>> See, I can burn strawmen too. ;-) >> >>:-) > >Yep, Joerg, Sometimes _even_ _you_ can toss out strawmen and be >aggravating ;-) > > ...Jim Thompson Just the same, krw was being a twit. |