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Old 11th March 2010, 01:35 PM   #141
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Originally Posted by Vikt0r View Post
Your'e right, I wasn't precise enough. Just to add - I didn't have an intention to blame anyone, especially not TI's engineers - rather I wanted to highlight a possible problem. Honestly, I didn't think the subject will cause such amount of feedback, therefore I didn't struggle too much to share all the prerequisites of my conclusions.
Again, I would be happy if I'm wrong and something went wrong due to my specific mistake, but, based on "test, collect&conclude" I had to conclude, that everything's fine with my design, the reason is somewhere behind.
One option would be (if that is possible) to measure the current from the two analog and the digital supply when sut down, to see if there is a specific one that causes the heating. That could lead to a direction where to look. Also the DC output voltage when shut down (if not zero) could be a clue.

jd
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Old 11th March 2010, 02:06 PM   #142
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Originally Posted by janneman View Post
One option would be (if that is possible) to measure the current from the two analog and the digital supply when sut down, to see if there is a specific one that causes the heating. That could lead to a direction where to look. Also the DC output voltage when shut down (if not zero) could be a clue.

jd
Unfortunately, that's not possible already, as I have thrown away the defective chip and installed a new one...But. The heating were caused definitely by both analog supplies. Didn't need to measure - the +5V digital supply was staying cold, while both +15V and -15V analog regulator chips (
Lm317/337) were very hot, the only reason they remained alive - that I installed them on excessive heatsinks, which went very hot (was not possible to hold the finger on them). Normally I would also suspect an oscillation, but again - I had a case, where this occured during normal operation. The root cause was most probably a power-line spike/noise which forced the IC to "hang up" - and in such condition it started to act as a heater drawing current from both analog PS lines.
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Old 11th March 2010, 02:50 PM   #143
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Originally Posted by Vikt0r View Post
[snip]The root cause was most probably a power-line spike/noise which forced the IC to "hang up" - and in such condition it started to act as a heater drawing current from both analog PS lines.
How do you know that? Do you mean a power line spike from the mains getting through to the output of your regulators?

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Old 11th March 2010, 04:07 PM   #144
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Yesterday I had an issue with PGA2310, want to post it here to check if someone may had similar thing. So, my PGA suddenly died. In the evening I turned off the device just usually (staying in standby, so the PGA and controller were on), and in the morning when I turned it on - it didn't work anymore.
On the PCB around the PGA traces of overheating are visible - the fiberglass even turned slightly brown, which means that for some reason the PGA just burned... Also, when I touched it (wasn't working already) it was still very hot.
I'm glad I saw this post (I don't check this site as much as I should, I guess). I've built a few pga boards (pc, perf, even hand wiring) and some of them have done this 'heating' thing on me! I thought it was my hacked up PSU (using a rail splitter chip to take 10v and make 2 fives from it, etc). I would remove power if the chip 'got hot' and let it cool for a bit then reapply power. it would always work fine after that but I never found what put it in that state. my controller is an arduino (in all cases) and I can't really blame the controller; it always seems to be working fine.

this happens on the DIP version (5v version) more often but I've seen it on the smd (12v version) sometimes, as well.
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Old 11th March 2010, 06:13 PM   #145
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I'm glad I saw this post (I don't check this site as much as I should, I guess). I've built a few pga boards (pc, perf, even hand wiring) and some of them have done this 'heating' thing on me! I thought it was my hacked up PSU (using a rail splitter chip to take 10v and make 2 fives from it, etc). I would remove power if the chip 'got hot' and let it cool for a bit then reapply power. it would always work fine after that but I never found what put it in that state. my controller is an arduino (in all cases) and I can't really blame the controller; it always seems to be working fine.

this happens on the DIP version (5v version) more often but I've seen it on the smd (12v version) sometimes, as well.
I looked through the data sheet to see if it said anything about the power up sequence. Soms chips are critical with regard to that, they for instance want the digital supply to be up and stable before you should bring up the analog supplies, or something like that.
Didn't find anything though; anybody has more info on that for the PGA's?

jd
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Old 11th March 2010, 07:30 PM   #146
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in my case, it had nothing at all to do with init'ing the chip. this would happen hours or even days after clean steadystate operation. it would just come out of nowhere.

once it gets into that run-away state, only a power cycle would fix it (sending bytes to it over the ctl channel does nothing)
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Old 11th March 2010, 07:38 PM   #147
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How do you know that? Do you mean a power line spike from the mains getting through to the output of your regulators?

jd
Exactly. I simply can't suspect anything else than power-line related instability.

Last edited by Vikt0r; 11th March 2010 at 07:44 PM.
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Old 11th March 2010, 07:43 PM   #148
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in my case, it had nothing at all to do with init'ing the chip. this would happen hours or even days after clean steadystate operation. it would just come out of nowhere.

once it gets into that run-away state, only a power cycle would fix it (sending bytes to it over the ctl channel does nothing)
This is 1:1 similar to my experience. It's definitely not from nowhere. The fact itself wouldn't be that much a problem, if there would be any kind of protection circuit within the IC. But there's not, obviously.
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Old 11th March 2010, 08:12 PM   #149
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Exactly. I simply can't suspect anything else [snip].
Try

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Old 12th March 2010, 02:27 AM   #150
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Viktor, picture would help. Maybe somehing wrong with analogue supply, LM3x7 have internal thermal protection. I thing you should measure 5v power supply. Just to make sure there is no over voltage in power supply.
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