day shot to hell
John Larkin
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
Martin Riddle
"John Larkin" <jjla...@highNOTlandTHIStechnologyPART.com> wrote in
message news:u0beg512h0fcels3a...@4ax.com...
Yea, know the feeling.
Most people I've talked to agree that the first board always has some
sort of problem(s).
Cheers
don
> ftp://jjlarkin.lmi.net/First.JPG
> ftp://jjlarkin.lmi.net/Swapped.jpg
>
Hi John and all,
This is a good example of what Jim was talking about.
Inside Thunderbird, I click these links and up pops up I.E.
I have checked Thunderbird for what it wants to call for ftp links.
I do not find any config settings for this.
Does anyone know how to re-configure Thunderbird to call Firefox instead.
Thanks
don
Joel Koltner
news:u0beg512h0fcels3a...@4ax.com...
I (cough!) think most of us have had that happen...
What's the big yellow silkscreened square around the oscillator-in-a-can for?
Metal shield maybe?
---Joel
Joerg
> 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 :-(
>
> Hi John and all,
>
> This is a good example of what Jim was talking about.
>
> Inside Thunderbird, I click these links and up pops up I.E.
>
> I have checked Thunderbird for what it wants to call for ftp links.
>
> I do not find any config settings for this.
>
> Does anyone know how to re-configure Thunderbird to call Firefox instead.
>
My Thunderbird does not do that, never did. Check Windows for
preferences, IOW which program a certain file suffix launches. If no
dice: Best may be to hose it all off your computer and do a clean slate
install of Firefox and if that doesn't do the trick, Thunderbird as
well. But save the bookmarks, email, addresses and whatever else you need.
--
Regards, Joerg
http://www.analogconsultants.com/
"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
Joerg
> "John Larkin" <jjla...@highNOTlandTHIStechnologyPART.com> wrote in message
> news:u0beg512h0fcels3a...@4ax.com...
>> The resistor that's screened "R127" is actually R129. And vice versa.
>
> I (cough!) think most of us have had that happen...
>
Mine were usually followed by ... phut ... *PHOOMP*
> What's the big yellow silkscreened square around the oscillator-in-a-can for?
> Metal shield maybe?
>
It's probably the no-step area, per ISO-9000 :-)
Phil Hobbs
Better complain to the head of Engineering. ;)
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
John Larkin
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
Joerg
Make an SCR crowbar with a TL431 pulling the trigger. I did a design
where a >$10k laser is connected to it. The LV rail needed super
protection because it could somehow cause the laser to commit suicide.
They wanted it to kick in between 3.6V and 3.7V. Built it here in the
lab, shipped it to them. So they fired it up, cranked that rather large
supply ... 3.63V ... 3.64V ... 3.65V ... *TUNGGG* ... they were impressed.
a7yvm1...@netzero.com
I usually produce an "assembly drawing" where another layer of text
contains the refdes inside the part outline.
This refdes text is defined at the library level and is never moved by
hand except when the component moves.
This drawing is produced separately from the silkscreen and is shipped
to the assembly house.
This is the reference, not the silkscreen.
Joerg
Typically this is done via the XYRS file which feeds into the placement
machine. So theoretically all this could not possibly have happened, but
... then there's reality. On my last one they had one chip 180 degrees
rotated. On all boards :-(
John Larkin
There will be an aluminum cover over the OCXO, more to keep air
currents off of it than as an EMI shield. That yellow thing was
supposed to be bare copper, not screened, but it is kind of cute this
way. The cover will get grounded by the mounting hardware anyhow.
It's impressive how nice of a phase noise improvement you can get by
keeping air flow off XOs, even cheap ones. Ditto reducing 1/f noise in
opamps.
We've found a few mistakes on this board so far... luckily none are
fatal and none require serious kluges. Mostly minor mechanical things
that annoy manufacturing.
I didn't ground HSWP_EN on the FPGA (we used it as a signal pin) so
all the lines that drive the many TTL interface chips float until the
FPGA is configured. Some of them randomly go linear and get quite hot
(fun to watch on the FLIR) and almost bog down the 3.3 volt switcher.
Luckily I can pull down HSWP with a resistor, which adds weak pullups
at powerup time, fixing that problem.
I will breathe serious sighs of relief when the PCIe link works and
the FPGA configures.
John
John Larkin
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. 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.
John
Joerg
> On Fri, 20 Nov 2009 17:26:06 -0800, Joerg <inv...@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
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.
> ... 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 :-)
krw
Our automatic insertion tools would never make this mistake. They
make a *lot* of others, but not this one. :-(
>Better complain to the head of Engineering. ;)
Fire the manufacturing manager. ;-)
krw
wrote:
We now back-annotate the placement information into the schematic and
use Crapture to generate a BOM with placement information. This is
released to manufacturing via an ECO and sucked into the pick-n-place
machine. The layout guy does produce an "assembly drawing" but it's
only use is in inspection. When the two disagree the released BOM is
"right". Only engineering can change the BOM, via another ECO) if
there is a disagreement. Well, that's the process, anyway.
Nico Coesel
>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
:-)
--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
"If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------
Raveninghorde
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.
Joerg
That often doesn't not help. Many switcher do nothing intil the UVLO
threshold is exceeded, and then they step on it with gusto. You may not
have enough time to rip out the banana plug before phssseee ... *POOF*
krw
With switchers this rarely does anything and often makes things even
worse.
John Larkin
wrote:
>John Larkin wrote:
>> On Fri, 20 Nov 2009 17:26:06 -0800, Joerg <inv...@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.
>
>
>> ... 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.
John
John Larkin
wrote:
>John Larkin <jjla...@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!
I did take the board home at night to do some of the placement and
routing myself, for the analog front end, some fast stuff, and the
switcher region. So it may well be my fault. She's learning fast, so I
suspect this will go on her evolving checklist and it's not likely to
happen again. There are probably 30 to 50 things one should check
before releasing gerbers, and it's easy to forget a couple. We need a
checklist.
All the supplies are working now. On Monday I'll have them put two new
BGAs on the board and see what happens next. Bringing up a new board
of this complexity is always, well, tense.
John
John Larkin
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.
John
Raveninghorde
wrote:
This depends on the topology of the switchers. I normally use buck
regulators but I admit that it doesn't work with other topologies.
krw
Often doesn't work with buck regulators either. Depending on what
they're driving startup can get quite nasty.
krw
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
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.
Joerg
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
Joerg
> On Sat, 21 Nov 2009 18:44:44 GMT, ni...@puntnl.niks (Nico Coesel)
> wrote:
>
>> John Larkin <jjla...@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?
[...]
Joerg
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.
Mycelium
wrote:
I thought transzorbs were the current norm.
Joerg
Too much lot tolerance, usually. A chip that works nicely at 3.3V might
go kaputt at 3.7V so you don't have much wiggle room.
krw
wrote:
>John Larkin wrote:
Use an FPGA that's not so finicky. They're all better than they were
but some have no sequencing requirements at all.
>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.
Comparitors with references are expensive. I'm surprised that you
even know they exist. ;-) With money to burn, the ones with the
variable hysterias input switch are pretty nice too (ADCMP343, etc.).
>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.
If you want belt and suspenders, what about a pass FET on the input?
>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.
Usually, the normal board variance is more than one that of one device
failing. Fuses, PTCs, and the like are pretty poor at this.
Unless a model specifically addresses an operational mode, assume it
doesn't. If it says it does, be very skeptical. Manufactrurer's
public models are pretty damned lousy.
Joerg
> On Sat, 21 Nov 2009 12:59:52 -0800, Joerg <inv...@invalid.invalid>
> wrote:
>
>> John Larkin wrote:
[...]
>>> 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
>
> Use an FPGA that's not so finicky. They're all better than they were
> but some have no sequencing requirements at all.
>
>> 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.
>
> Comparitors with references are expensive. I'm surprised that you
> even know they exist. ;-) ...
Well, on a recent design I had to. Dozens of components that all had to
fit into the space of a postage stamp. It was one of the few projects
where the BOM budget was huge, at least from my usual perspective. I
still ended up under 50% of it :-)
> ... With money to burn, the ones with the
> variable hysterias input switch are pretty nice too (ADCMP343, etc.).
>
>> 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.
>
> If you want belt and suspenders, what about a pass FET on the input?
>
That could also fail. I prefer sacrificial parts for this such as fuses
or fuse-resistors.
>> 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.
>
> Usually, the normal board variance is more than one that of one device
> failing. Fuses, PTCs, and the like are pretty poor at this.
>
Fuses are excellent. SCR shunts the rail, holds it there for a brief
moment ... phut ... fuse lets go.
> Unless a model specifically addresses an operational mode, assume it
> doesn't. If it says it does, be very skeptical. Manufactrurer's
> public models are pretty damned lousy.
This one has a problem that the reference shoot up to the VCC rail and
then slowly comes back. IOW it isn't very suitable for power-up
protection or sequencing.
John Larkin
wrote:
You can buy a 3.3 volt transzorb. It will sink lots of current at
about 6 volts.
http://www.vishay.com/doc?88940
John
krw
wrote:
>krw wrote:
>> On Sat, 21 Nov 2009 12:59:52 -0800, Joerg <inv...@invalid.invalid>
>> wrote:
>>
>>> John Larkin wrote:
>
>[...]
>
>>>> 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
>>
>> Use an FPGA that's not so finicky. They're all better than they were
>> but some have no sequencing requirements at all.
>>
>>> 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.
>>
>> Comparitors with references are expensive. I'm surprised that you
>> even know they exist. ;-) ...
>
>
>Well, on a recent design I had to. Dozens of components that all had to
>fit into the space of a postage stamp. It was one of the few projects
>where the BOM budget was huge, at least from my usual perspective. I
>still ended up under 50% of it :-)
They're too expensive as "protection devices" even for me.
>> ... With money to burn, the ones with the
>> variable hysterias input switch are pretty nice too (ADCMP343, etc.).
>>
>>> 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.
>>
>> If you want belt and suspenders, what about a pass FET on the input?
>>
>
>That could also fail. I prefer sacrificial parts for this such as fuses
>or fuse-resistors.
ANything can fail. How many belts do you wear with your suspenders?
Fuses are ugly. Customers with blown fuses even more so. THe owner
got a ration a few weeks back because we made the television (official
time out for equipment failure). ...and it wasn't even our fuse. They
had the crate closed up so didn't hear the UPS bitching either.
>>> 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.
>>
>> Usually, the normal board variance is more than one that of one device
>> failing. Fuses, PTCs, and the like are pretty poor at this.
>>
>
>Fuses are excellent. SCR shunts the rail, holds it there for a brief
>moment ... phut ... fuse lets go.
Fuses have very poor tolerances. A 2A fuse my let something go phut
at 5A. The electronics is there to protect the fuse.
>> Unless a model specifically addresses an operational mode, assume it
>> doesn't. If it says it does, be very skeptical. Manufactrurer's
>> public models are pretty damned lousy.
>
>
>This one has a problem that the reference shoot up to the VCC rail and
>then slowly comes back. IOW it isn't very suitable for power-up
>protection or sequencing.
Just sequence its power!
Joerg
> On Sat, 21 Nov 2009 13:18:08 -0800, Joerg <inv...@invalid.invalid>
> wrote:
>
>> Mycelium wrote:
>>> On Sat, 21 Nov 2009 12:59:52 -0800, Joerg <inv...@invalid.invalid>
>>> wrote:
>>>
>>>> John Larkin wrote:
[...]
>>>>> 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.
>>
>> Too much lot tolerance, usually. A chip that works nicely at 3.3V might
>> go kaputt at 3.7V so you don't have much wiggle room.
>
> You can buy a 3.3 volt transzorb. It will sink lots of current at
> about 6 volts.
>
> http://www.vishay.com/doc?88940
>
Ok, but at 6V it'll be way too late for whatever logic stuff hangs on
that rail.
Joerg
> On Sat, 21 Nov 2009 13:30:00 -0800, Joerg <inv...@invalid.invalid>
> wrote:
>
>> krw wrote:
>>> On Sat, 21 Nov 2009 12:59:52 -0800, Joerg <inv...@invalid.invalid>
>>> wrote:
[...]
>>>> The only thing that really works with such low voltage levels and
>>>> finicky FPGA is precisely controlled crowbars. Either TL431-style or use
>>> Use an FPGA that's not so finicky. They're all better than they were
>>> but some have no sequencing requirements at all.
>>>
>>>> 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.
>>> Comparitors with references are expensive. I'm surprised that you
>>> even know they exist. ;-) ...
>>
>> Well, on a recent design I had to. Dozens of components that all had to
>> fit into the space of a postage stamp. It was one of the few projects
>> where the BOM budget was huge, at least from my usual perspective. I
>> still ended up under 50% of it :-)
>
> They're too expensive as "protection devices" even for me.
>
That's why I usually opt for a TL431 plus transistor plus SCR. If I have
the space which I sometimes don't.
>>> ... With money to burn, the ones with the
>>> variable hysterias input switch are pretty nice too (ADCMP343, etc.).
>>>
>>>> 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.
>>> If you want belt and suspenders, what about a pass FET on the input?
>>>
>> That could also fail. I prefer sacrificial parts for this such as fuses
>> or fuse-resistors.
>
> ANything can fail. How many belts do you wear with your suspenders?
If a few hundred bucks worth of FPGA hang on it I'd say at least one :-)
> Fuses are ugly. Customers with blown fuses even more so. THe owner
> got a ration a few weeks back because we made the television (official
> time out for equipment failure). ...and it wasn't even our fuse. They
> had the crate closed up so didn't hear the UPS bitching either.
>
It's the last resort. Still better than a unit belching smoke.
>>>> 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.
>>> Usually, the normal board variance is more than one that of one device
>>> failing. Fuses, PTCs, and the like are pretty poor at this.
>>>
>> Fuses are excellent. SCR shunts the rail, holds it there for a brief
>> moment ... phut ... fuse lets go.
>
> Fuses have very poor tolerances. A 2A fuse my let something go phut
> at 5A. The electronics is there to protect the fuse.
>
You'd be surprised what a li'l DPAK SCR can do. It has no problem
blowing at fuse at 5A or 10A.
>>> Unless a model specifically addresses an operational mode, assume it
>>> doesn't. If it says it does, be very skeptical. Manufactrurer's
>>> public models are pretty damned lousy.
>>
>> This one has a problem that the reference shoot up to the VCC rail and
>> then slowly comes back. IOW it isn't very suitable for power-up
>> protection or sequencing.
>
> Just sequence its power!
Couldn't. In that case power was the actual control signal and things
had to happen fast, within hundreds of usec. Now they do :-)
Nico Coesel
If possible I assemble prototypes in different phases. Starting with
the power supply. Another option is removing filtering components. I
usually have beads at PSU outputs. Removing those isolates the PSU
from the rest of the circuit.
krw
wrote:
>Raveninghorde <raveninghorde@invalid> wrote:
Assembling things in stages just pisses off the manufacturing folk.
Our boards usually have far too many components to do manually.
Sometimes not, but they're too simple to not work. ;-)
krw
wrote:
Few hundred bucks? Jeorg, I'm ashamed of you. ;-)
I've really never been scared of taking out an FPGA, even when they
were a few thou$and. The sort of thing we're talking about is a
bring-up issue which is something I'd rather not spend any significant
BOM cost on. That's a cost that keeps on taking.
>> Fuses are ugly. Customers with blown fuses even more so. THe owner
>> got a ration a few weeks back because we made the television (official
>> time out for equipment failure). ...and it wasn't even our fuse. They
>> had the crate closed up so didn't hear the UPS bitching either.
>>
>
>It's the last resort. Still better than a unit belching smoke.
Fuses to limit smoke, sure, but that's not going to save any
electronics. The idea of fuses is to keep the damage inside the
covers. Fuses just aren't accurate/fast enough to protect circuits.
>>>>> 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.
>>>> Usually, the normal board variance is more than one that of one device
>>>> failing. Fuses, PTCs, and the like are pretty poor at this.
>>>>
>>> Fuses are excellent. SCR shunts the rail, holds it there for a brief
>>> moment ... phut ... fuse lets go.
>>
>> Fuses have very poor tolerances. A 2A fuse my let something go phut
>> at 5A. The electronics is there to protect the fuse.
>>
>
>You'd be surprised what a li'l DPAK SCR can do. It has no problem
>blowing at fuse at 5A or 10A.
>
I just don't see the purpose, on small stuff. 100A, maybe.
>>>> Unless a model specifically addresses an operational mode, assume it
>>>> doesn't. If it says it does, be very skeptical. Manufactrurer's
>>>> public models are pretty damned lousy.
>>>
>>> This one has a problem that the reference shoot up to the VCC rail and
>>> then slowly comes back. IOW it isn't very suitable for power-up
>>> protection or sequencing.
>>
>> Just sequence its power!
>
>
>Couldn't. In that case power was the actual control signal and things
>had to happen fast, within hundreds of usec. Now they do :-)
I meant sequence the power to the reference. ;-)
Jim Thompson
>On Sat, 21 Nov 2009 14:14:15 -0800, Joerg <inv...@invalid.invalid>
>wrote:
>
[snip]
>>>>
>>>> This one has a problem that the reference shoot up to the VCC rail and
>>>> then slowly comes back. IOW it isn't very suitable for power-up
>>>> protection or sequencing.
>>>
>>> Just sequence its power!
>>
>>
>>Couldn't. In that case power was the actual control signal and things
>>had to happen fast, within hundreds of usec. Now they do :-)
>
>I meant sequence the power to the reference. ;-)
Any reference that "shoot(s) up to the VCC rail" should be replaced
with one that doesn't. Where do you buy such crap?
As for fuses, I've always been fond of crowbar fuse blowers when
over-voltage conditions occur. Why lose downstream electronics when a
power supply goes bananas?
...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 |
Opa, Do all fairy tales begin with
"Once Upon A Time?"
No Darling, There is a whole series
of fairy tales that begin with
"If Elected I Promise"
Joerg
> On Sun, 22 Nov 2009 10:10:35 -0600, krw <k...@att.bizzzzzzzzzzz> wrote:
>
>> On Sat, 21 Nov 2009 14:14:15 -0800, Joerg <inv...@invalid.invalid>
>> wrote:
>>
> [snip]
>>>>> This one has a problem that the reference shoot up to the VCC rail and
>>>>> then slowly comes back. IOW it isn't very suitable for power-up
>>>>> protection or sequencing.
>>>> Just sequence its power!
>>>
>>> Couldn't. In that case power was the actual control signal and things
>>> had to happen fast, within hundreds of usec. Now they do :-)
>> I meant sequence the power to the reference. ;-)
>
> Any reference that "shoot(s) up to the VCC rail" should be replaced
> with one that doesn't. Where do you buy such crap?
>
Later per PM.
> As for fuses, I've always been fond of crowbar fuse blowers when
> over-voltage conditions occur. Why lose downstream electronics when a
> power supply goes bananas?
>
Exactamente!
krw
<To-Email-Use-Th...@My-Web-Site.com> wrote:
>On Sun, 22 Nov 2009 10:10:35 -0600, krw <k...@att.bizzzzzzzzzzz> wrote:
>
>>On Sat, 21 Nov 2009 14:14:15 -0800, Joerg <inv...@invalid.invalid>
>>wrote:
>>
>[snip]
>>>>>
>>>>> This one has a problem that the reference shoot up to the VCC rail and
>>>>> then slowly comes back. IOW it isn't very suitable for power-up
>>>>> protection or sequencing.
>>>>
>>>> Just sequence its power!
>>>
>>>
>>>Couldn't. In that case power was the actual control signal and things
>>>had to happen fast, within hundreds of usec. Now they do :-)
>>
>>I meant sequence the power to the reference. ;-)
>
>Any reference that "shoot(s) up to the VCC rail" should be replaced
>with one that doesn't. Where do you buy such crap?
>
>As for fuses, I've always been fond of crowbar fuse blowers when
>over-voltage conditions occur. Why lose downstream electronics when a
>power supply goes bananas?
I guess that depends on the application. I'm more worried abut
fuse-blowers getting too happy than even attempting to save any
downstream electronics. In my case, the large cost is the service
outage, not the electronics.
Jim Thompson
I was protecting $1000's of dollars of custom-made stuff. I could
make a 10A fuse element vanish is micro-seconds
(filter-cap-bus-bar-SCR loop) ;-)
...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 |
Obama: Master of Opaque Transparency
Jim Thompson
wrote:
>Jim Thompson wrote:
>> On Sun, 22 Nov 2009 10:10:35 -0600, krw <k...@att.bizzzzzzzzzzz> wrote:
>>
>>> On Sat, 21 Nov 2009 14:14:15 -0800, Joerg <inv...@invalid.invalid>
>>> wrote:
>>>
>> [snip]
>>>>>> This one has a problem that the reference shoot up to the VCC rail and
>>>>>> then slowly comes back. IOW it isn't very suitable for power-up
>>>>>> protection or sequencing.
>>>>> Just sequence its power!
>>>>
>>>> Couldn't. In that case power was the actual control signal and things
>>>> had to happen fast, within hundreds of usec. Now they do :-)
>>> I meant sequence the power to the reference. ;-)
>>
>> Any reference that "shoot(s) up to the VCC rail" should be replaced
>> with one that doesn't. Where do you buy such crap?
>>
>
>Later per PM.
>
>
[snip]
I just designed a POR/Reference that does this sequence...
(1) Verify supply is at least 3 CMOS thresholds
(2) Verify Reference potential has reached regulation
(3) Verify VDD has reached minimum per specification
(4) Verify an additional input (monitoring switcher) is reporting OK
(4) Time-out for 100mS (on-chip oscillator and 14-stage counter ;-)
(5) Release RESETbar
...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 |
Ability without honor is useless.
- Marcus Tullius Cicero
krw
<To-Email-Use-Th...@My-Web-Site.com> wrote:
The price may be (tens of) $1000s of dollars, but the cost certainly
isn't. ;-) OTOH, a royally pissed off customer might easily be worth
40dB more. The boss doesn't like it when we're the subject of the
television program.
krw
...but transistors are free, packages are not.
Jim Thompson
If that were packaged by itself it would be only 4-pins (or 6-pin if
you'd like to use the reference ;-)
In this case it's about 5% of the total chip function.
...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 |
The AMA represents only 19% of doctors, and only that high if you
count student members. In Obama-talk that's considered consensus.
krw
<To-Email-Use-Th...@My-Web-Site.com> wrote:
Would you do it at $1-$2 per supply?
Jim Thompson
If I made such a function as a custom part? Sure?
...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 |
If you wanted a President with balls why didn't you elect Hillary?
krw
<To-Email-Use-Th...@My-Web-Site.com> wrote:
You mean as part of the spec? Well, of course. I meant as an added
expense just in case...
Joerg
Let's put it that way: If the crowbar trips something else _has_ already
failed. Meaning it's a service call no matter what. The difference
between having a crowbar or not having one could be several thousand
bucks (board repairable versus it being toastissimo). It can also
prevent plumes of smoke and a rather embarrassing case where the fire
engines had to come out because the automatic fire alarm and the
sprinklers came on, damaging all sorts of other equipment.
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.
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.
krw
wrote:
Right. The difference is the cost, not the price. The cost of the
electronics is certainly not in the tens of thousands of dollars. The
stuff I did where the cost was in the millions had all sorts of belts
on. With supplies rated in the kA, things get smoky fast and smoke
was rather more frowned upon. These weren't jellybean regulators,
though.
>It can also
>prevent plumes of smoke and a rather embarrassing case where the fire
>engines had to come out because the automatic fire alarm and the
>sprinklers came on, damaging all sorts of other equipment.
Fuses are there to keep the heat, if not a little smoke, inside. Fans
dissipate the rest rather quickly. ;-)
>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.
>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.
See, I can burn strawmen too. ;-)
Joerg
With a bunch of hotshot FPGA you can easily get to $1k. Many of my
boards drive very expensive gear.
>> It can also
>> prevent plumes of smoke and a rather embarrassing case where the fire
>> engines had to come out because the automatic fire alarm and the
>> sprinklers came on, damaging all sorts of other equipment.
>
> Fuses are there to keep the heat, if not a little smoke, inside. Fans
> dissipate the rest rather quickly. ;-)
>
See, that's why fuses are a good thing :-)
>> 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. ;-)
:-)
Jim Thompson
wrote:
>krw wrote:
>> On Sun, 22 Nov 2009 13:32:09 -0800, Joerg <inv...@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 ;-)
krw
wrote:
Sure, the Virtex-IIs and 4's I last used were about $4K each. Even
here a service call at the wrong time (incoming shells) makes that
chump change. That's not the point though. I don't spend a lot of
money to protect bring-up (which was the original point). We'll put
in 0-ohm resistors for debug but that's about it.
BTW, the FPGA I'm most likely to use next[*] is more like $2.
[*] Firmware is so hosed up there isn't much point in making new
hardware to play with.
>>> It can also
>>> prevent plumes of smoke and a rather embarrassing case where the fire
>>> engines had to come out because the automatic fire alarm and the
>>> sprinklers came on, damaging all sorts of other equipment.
>>
>> Fuses are there to keep the heat, if not a little smoke, inside. Fans
>> dissipate the rest rather quickly. ;-)
>>
>
>See, that's why fuses are a good thing :-)
I never said I didn't use fuses, only that I don't have any illusions
of them saving electronics. As I said before, their purpose is to
keep any fire inside the covers.
>>> 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.
Circuits that never fail? Why don't you just use one of them on the
power supply, instead? ;-)
>
>>> 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.
That's the theory. Reality is much different, of course.
Greg Neff
<jjla...@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.
gr...@guesswhichwordgoeshere.com
John Larkin
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
JosephKK
<raveninghorde@invalid> wrote:
>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.
JosephKK
Just the same, krw was being a twit.
JosephKK
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
Interesting power distribution used there.
John Larkin
We're using an external 12 volt supply and one of these
http://www.mini-box.com/s.nl/sc.8/category.13/.f
which plugs into the mini-ITX processor board. Switched +12 and +5
come out of it and power our spectrosopy board (which has 5 more
switchers and 3 linear regs of its own) and has power distribution for
the hard drives. Seems to work.
This instrument is basically a PC, but we don't want it to look like a
PC. Most PCs are wiring hairballs inside.
That AC powered fan is temporary. We'll use a temperature-controlled
DC fan in the real rackmount box. The Kontron has a connector for
that.
John
JosephKK
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
Kinda cute. Nice to know such exists.