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From: krw on 21 Nov 2009 15:46 On Sat, 21 Nov 2009 12:20:27 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Sat, 21 Nov 2009 13:35:01 -0600, krw <krw(a)att.bizzzzzzzzzzz> wrote: > >>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. >> >>With switchers this rarely does anything and often makes things even >>worse. > >Yes. The only thing to do is to isolate the power section from the >loads and bring up the supplies unloaded. That requires jumpers or >whatever. I do have LC filters between the supply pours and the main >pours, and in retrospect I should have removed the inductors and >tested the supplies. We generally put 0-ohm resistors on supply inputs. We do it mainly to be able to measure the current but this has also helped pass EMI a couple of times. Ferrites fit nicely where 0-ohm resistors once were. ;-) >Given the consequences of power supply failure, I'm leaning more >towards always incorporating transzorbs/clamps/crowbars on things like >this. Given that this sort of thing is a pre-production hazard, I don't see it worth spending much money or effort on. Have you had any bzzzt-BANGs in manufacturing? We do once in a while but rarely on supplies. There are just so many places this can happen that it doesn't seem reasonable to attack only a minor source of smoke.
From: Joerg on 21 Nov 2009 15:46 John Larkin wrote: > On Sat, 21 Nov 2009 10:04:18 -0800, Joerg <invalid(a)invalid.invalid> > wrote: > >> John Larkin wrote: >>> On Fri, 20 Nov 2009 17:26:06 -0800, Joerg <invalid(a)invalid.invalid> >>> wrote: >>> >>>> don wrote: >>>>> John Larkin wrote: >>>>> >>>>>> ftp://jjlarkin.lmi.net/First.JPG >>>>>> ftp://jjlarkin.lmi.net/Swapped.jpg >>>>>> >>>> Hey John, you wasted lots of real estate there. Wish I could have some >>>> of that. Doing an EMC fix on a client design right now and I can't even >>>> shove one more 0402 part in there :-( >>>> >>> We have lots of space for this one. We're replacing an >>> older-generation board that is about 6x or so of our board area. >>> >>> You will be not-pleased to know that the switcher section has its own >>> rectangular ground plane section that is connected to the rest of the >>> plane through a number of thinnish slivers. ... >> >> Interestingly, one of the line items in my recommendations for this one >> is to pepper a similar isolated plane with vias to the ground plane. For >> EMC purposes, since this one must pass much stricter rules than the >> usual class B. > > I'm trading off potential switcher-harmonic noise (EMI test hazard) > against allowing switcher fundamentals to creep into other parts of > the board, where they would make birdies in my spectra right in the > region of interest. > > I have no idea whether any of this will work. > For EMI it works but in Europe they have put some lids on that trick. >>> ... The rows of inductors, >>> incoming and outgoing, straddle the plane gaps. The idea is to keep >>> the various circulating currents in the switchers from leaking into >>> the main ground plane where the analog stuff is. I did the >>> spread-spectrum thing on all the switchers, too. >>> >> Oh, how I wish I could do spread spectrum. But with the EMC measures so >> far I am already at a full 100% of available real estate. Unless someone >> knows a self-contained oscillator in an SC75 package :-) > > I'm using one tiny logic schmitt as an RC oscillator. The resulting > triangle, around 1 volt p-p, gets squirted into the Fset pin of each > of the switchers through a pretty big resistor, and that FMs the > switcher frequencies. That's not a lot of parts, but then I have a lot > of area available on this one. > My problem is that's three parts for the oscillator plus one 0201 resistor per switcher (I've got three). No dice :-( The board already looks like this: http://allfloridablog.com/wp-content/uploads/2009/11/eaa5eea19cvw-guiness.jpg -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 21 Nov 2009 15:49 John Larkin wrote: > On Sat, 21 Nov 2009 18:44:44 GMT, nico(a)puntnl.niks (Nico Coesel) > wrote: > >> 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 >> I assume The Brat can kiss her Christmas invitation goodbye this year >> :-) > > But then maybe I couldn't drive her jeep! > Hey, didn't she pay that with college "savings" which ultimately came out of your pocket? [...] -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 21 Nov 2009 15:59 John Larkin wrote: > On Sat, 21 Nov 2009 13:35:01 -0600, krw <krw(a)att.bizzzzzzzzzzz> wrote: > >> 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. >> With switchers this rarely does anything and often makes things even >> worse. > > Yes. The only thing to do is to isolate the power section from the > loads and bring up the supplies unloaded. That requires jumpers or > whatever. I do have LC filters between the supply pours and the main > pours, and in retrospect I should have removed the inductors and > tested the supplies. > > Given the consequences of power supply failure, I'm leaning more > towards always incorporating transzorbs/clamps/crowbars on things like > this. > The only thing that really works with such low voltage levels and finicky FPGA is precisely controlled crowbars. Either TL431-style or use one of those newfangled comparators in DFN packages that have a reference built in. The ones with push-pull outputs ought to be able to fire an SCR directly. This also afford the chance to shut down when a sequencing rule is being violated. Another option is to yank the shut-down or slow-start pin. Of course that won't help if the root cause is a blown FET in a buck. Also, there must be something in front of the board that could gracefully blow open without causing the sirens to go off. With comparators be careful, I just unearthed an undocumented nastiness upon power-up in one. Do _not_ trust SPICE models. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Mycelium on 21 Nov 2009 16:05
On Sat, 21 Nov 2009 12:59:52 -0800, Joerg <invalid(a)invalid.invalid> wrote: >John Larkin wrote: >> On Sat, 21 Nov 2009 13:35:01 -0600, krw <krw(a)att.bizzzzzzzzzzz> wrote: >> >>> 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. >>> With switchers this rarely does anything and often makes things even >>> worse. >> >> Yes. The only thing to do is to isolate the power section from the >> loads and bring up the supplies unloaded. That requires jumpers or >> whatever. I do have LC filters between the supply pours and the main >> pours, and in retrospect I should have removed the inductors and >> tested the supplies. >> >> Given the consequences of power supply failure, I'm leaning more >> towards always incorporating transzorbs/clamps/crowbars on things like >> this. >> > >The only thing that really works with such low voltage levels and >finicky FPGA is precisely controlled crowbars. Either TL431-style or use >one of those newfangled comparators in DFN packages that have a >reference built in. The ones with push-pull outputs ought to be able to >fire an SCR directly. This also afford the chance to shut down when a >sequencing rule is being violated. > >Another option is to yank the shut-down or slow-start pin. Of course >that won't help if the root cause is a blown FET in a buck. > >Also, there must be something in front of the board that could >gracefully blow open without causing the sirens to go off. With >comparators be careful, I just unearthed an undocumented nastiness upon >power-up in one. Do _not_ trust SPICE models. I thought transzorbs were the current norm. |