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computerpie
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Re: Ethernet chip gets raging hot

Mon Jul 23, 2012 1:12 am

jojopi wrote:
The LAN9512 is powered from the 3V3 rail and has no connection at all to the 5V input. So I do not believe that the quality of the 5V supply can have any effect on its power dissipation.
Ok well I am seeing a definite difference. So whats changed on my board?
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mahjongg
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Re: Ethernet chip gets raging hot

Mon Jul 23, 2012 1:29 am

The lan9512 chip doesn't only control ethernet, it also controls USB, and notable ethernet is just another USB device, so "turning it on" by plugging in an ethernet cable equals to adding another USB device to the equation. USB devices are 5V devices, so having a stable 5V might have some influence on how the whole USB "ecosystem" behaves, perhaps significantly reducing traffic somehow, as USB is actually a balanced serial high speed connection, terminated with 100 Ohm, it also needs a fair amount of power, and maybe if there are "conflicts" like two USB drivers trying to control the bus at the same time, it takes much more (i'm just thinking aloud here) which may be the cause of this particular chip heating up somewhat. Its a pity its not easy to cut the 3V3 feed to this chip somewhere to see how much current it is using.

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computerpie
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Re: Ethernet chip gets raging hot

Mon Jul 23, 2012 1:48 am

I keep seeing people talking about touching a chip isn't a precise way of knowing what temps its running at.
That is true and I'm sure most people understand that.
I've been designing embedded/electronic systems for a long time and know that a good rule of thumb is "if you can't leave your finger on a device for a few minutes without discomfort there is something wrong" . If you don't deal with it ie.. heat sink, fan or design change then it's going to fail.
It might not be tomorrow or the next day but it will fail prematurely. Thats why there are tons of old Apple Imacs in the dump today. GPU running too hot and they are now dead. :lol:
Also the whole board runs off the 5v rail all other voltages are regulated off that.

Crap in gives you crap out. :?
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Mega
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Re: Ethernet chip gets raging hot

Mon Jul 23, 2012 1:52 am

computerpie wrote:I keep seeing people talking about touching a chip isn't a precise way of knowing what temps its running at.
That is true and I'm sure most people understand that.
I've been designing embedded/electronic systems for a long time and know that a good rule of thumb is "if you can't leave your finger on a device for a few minutes without discomfort there is something wrong" . If you don't deal with it ie.. heat sink, fan or design change then it's going to fail.
It might not be tomorrow or the next day but it will fail prematurely. Thats why there are tons of old Apple Imacs in the dump today. GPU running too hot and they are now dead. :lol:
Also the whole board runs off the 5v rail all other voltages are regulated off that.

Crap in gives you crap out. :?
Yeah, but do you normally work with SoC embedded projects?

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computerpie
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Re: Ethernet chip gets raging hot

Mon Jul 23, 2012 2:00 am

[quote}
Yeah, but do you normally work with SoC embedded projects?[/quote]

What does that have to do with anything? All electronic devices are made of plastic, metals, and sand. Dissimilar materials heating and cooling expand and contract different rates. Something's gonna give!! :)
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pluggy
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Re: Ethernet chip gets raging hot

Mon Jul 23, 2012 12:16 pm

Silicon junctions fail at around 160 C and research done by the US military suggests that electronic devices life halves for every 10 C increase in temperature. but the life of an individual device isn't set. The life of a component running at 60 degrees could be several years, but it would be 8 times longer (several decades) if it was only running at 30. How much do you value a 25 quid device ?

My Pi which has now been up for approaching 5 days and doing a fair amount of work and network stuff every minute by cron jobs, CPU is running at around 46 C and the USB chip is at 48 C measured with an IR thermometer. Ambient is 21 C. Sticking you finger on a small device generating 0.7 watts of heat will cool it by a fair degree because the blood flowing through your finger will carry some of the heat away. What temperature causes pain will vary with climatic conditions, the heat capacity of the object and with the individual. I can put my finger on the USB chip and it feels warmish but putting my finger on a large water filled radiator at 48 C feels a lot more uncomfortable and I can't keep it there for more than a few seconds because my blood flow through my finger isn't going to have much on an impact on several dozen litres of water with a 20kW boiler on the end of it.
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bones0
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Re: Ethernet chip gets raging hot

Sun Sep 09, 2012 2:31 pm

A friend of mine just told me:

"Meiner Meinung nach sind die VDD18CORE Pins am LAN/USB Chip Ausgänge. Und die hängen sie an eine 1.8V Quelle."

Which means translated:
"In my opinion the VDD18CORE Pins at the LAN/USB Chip are outputs. And those are connected to a 1.8V Power Source".

If he's right we might have a clue. Even for a software guy like me connecting outputs to outputs sounds like not the best idea...

Regards
Peter

naplam
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Re: Ethernet chip gets raging hot

Sun Sep 09, 2012 2:42 pm

bones0 wrote:"In my opinion the VDD18CORE Pins at the LAN/USB Chip are outputs. And those are connected to a 1.8V Power Source".

If he's right we might have a clue. Even for a software guy like me connecting outputs to outputs sounds like not the best idea...
The problem has been solved in the new revision of the board. The lan chip was providing power to stuff other than itself, thus running quite hot.

bones0
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Re: Ethernet chip gets raging hot

Sun Sep 09, 2012 3:44 pm

OK, thanks. Didn't find the proper thread then ;-)

My Raspberries are rather unstable concerning USB/Ethernet. But I got a couple of coolers now; guess that will help. And they aren't expensive.

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Peter

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jojopi
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Re: Ethernet chip gets raging hot

Sun Sep 09, 2012 3:46 pm

naplam wrote:The problem has been solved in the new revision of the board. The lan chip was providing power to stuff other than itself, thus running quite hot.
The 1V8 connection was certainly an error. But neither logic nor evidence suggests that it caused significant overheating of IC3. The new board revision includes an area of copper on the bottom face under the LAN9512. I would expect that to cool the chip more than the fix does.

rocketero
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Re: Ethernet chip gets raging hot

Mon Feb 11, 2013 11:18 pm

I found a command line to check the temperature of the rpi, I don't know how trustable it is.

it's:

[email protected] $ vcgencmd measure_temp

Mine says it's 51.9 C (Celsius) after running for almost 1 day. It's boxed so the external plastic box does not feel any hot at all.

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mahjongg
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Re: Ethernet chip gets raging hot

Mon Feb 11, 2013 11:47 pm

Its quite trustable but its also totally irrelevant to this old thread, which has become obsolete ever since the revision 2 board came out that solved a hardware bug that caused some LAN9512 USB hub/ethernet-adapter chips to get warmer than normal. You are talking about measuring the temperature of the Broadcom SoC, a completely different chip.

The LAN9512 chip doesn't get abnormally hot anymore since revision 2.0.

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