RG1 1.8v regulator

Just to expand on my original observations, the negative current I see on the output of RG1 seems to be due to it outputting 1.79v for a few seconds on initial powerup before stabilising at 1.804v. While the LAN9512 appears to power up at 1.805v and stay there.

My second order of Raspberry Pis arrived earlier in the week. A quick check shows one of them is running slightly warmer than the rest, not too much, I can still hold my finger on the LAN chip. I measure 1837mV at RG1 compared to 1793mV on one of the cooler ones (at idle, unmodified boards). Perhaps the LAN9512 core is running over voltage due to the external source and hence a bit hotter in this case. There may be multiple scenarios depending on components.

I don't expect it will reduce the life of the chip unless it gets really hot, so I'll leave the rest alone unless LAN chips start dying all over the place.

Selsinork

Thank you so much for this great piece of work, really helpful.  Cannot wait to try some FN1204xxxx,FN1205xxxxx boards with the same configuration.

I'll let you know how I get on.

(I wonder if this post will dissolve into the Ether as soon as I post? )

Cheers

Pete

PeteL wrote:

 

(I wonder if this post will dissolve into the Ether as soon as I post? )

You're in luck Pete!  The SHA-512 of the characters in the subject line multiplied by the current distance to Jupiter in furlongs added to the day of the week is not prime!

Or maybe Loki was so stunned at selsinork's awesome chart that he forgot his usual duties.

Morgaine.

Pete, if your examination of Pi design around the LAN9512 leads to board changes in that area, you might wish to consider the problem of self-powered USB hubs attempting to power the Pi upstream through their A-B lead, which typically fails and sends the Pi into a rapid continuous reboot cycle and a consequent rapid power cycling of attached HDMI equipment.

I reported it in a thread here -- http://www.element14.com/community/thread/19316?tstart=0

Unfortunately this affects an official Farnell "Pi Accessory" hub, and I'm sure it's not the only one.

Morgaine.

My IR thermometer arrived yesterday and I was able to take some more measurments. The laser sight is mounted off to the side, so it is necessary to scan around to find the hot spot. Measurements taken after 20min of video playback over network.

FN120508290 The first board the mod was applied to, still in a configuration where I can switch between the 1.8V power sources with a jumper.

  Powered from RG1 exclusively

    RG1 ____mV/IC3 ____mV idle (I forgot to measure this, will edit later as it might give an indication of each regulators ouput as a function of load)

    RG1 ____mV/IC3 ____mV playback

    45.7C

  Powered from IC3 exclusively

    RG1 ____mV/IC3 ____mV idle

    RG1 ____mV/IC3 ____mV playback

    49.1C - hot spot seems to be larger

FN120744907 The second board which seemed to be running a bit warmer from the beginning

  Unmodified (RG1 removed and replaced in previous test. Heat stress may have influenced result)

    1837mV idle

    49.9C playback

  RG1 removed

    1837mV idle

    50.7C playback

  Mod applied

    RG1 1795mV/IC3 1845mV idle

    RG1 ____mV/IC3 ____mV playback

    46.0C - 49.5C (initially 46.0C after 20mins video playback, but it continued to rise for another 5 minutes or so)

I thought I was getting consistent results until that last measurement. Not sure what happenned, maybe it needs more time to equilibriate or there was an action scene. I measured again after leaving it overnight and still read 47.2C and climbing after at least 20 mins _at idle_ (lan plugged in, but no traffic, no video playback), then after another 10 minutes back down to 46.0C. Maybe this is normal, at least we seem to have elliminated the dependance on video playback.

The results seem to suggest that powering the 1.8V rail from IC3 might account for up to 4 degrees higher temperature on IC3. Looks like there might be quite a bit of variation in the LAN9512 chips based on the observed variation of VDD18CORE voltage so some may be affected more so than others.

This doesn't really confirm if this bug is the source of the _really_ hot LAN chips, but my chips don't seem to be in that category anyway (50C seems to be the norm from what I see). Perhaps some chips handle this extra current drain more gracefully than others though.

Here is the second attempt at the mod

My IR thermometer arrived yesterday

I was looking at picking one up, but noticed that even rather expensive ones seem to have a minimum measurement 'spot' of something around 20mm which is rather larger than the lan9512. I was wondering just how that affects the readings..  Presumably they average the total emissions over whatever is in the sensors view somehow.

Like you I don't have a Pi that runs as hot as some reports, and without one it's difficult to form a theory on what the cause is.

selsinork wrote:

 

My IR thermometer arrived yesterday

I was looking at picking one up, but noticed that even rather expensive ones seem to have a minimum measurement 'spot' of something around 20mm which is rather larger than the lan9512. I was wondering just how that affects the readings..  Presumably they average the total emissions over whatever is in the sensors view somehow.

 

Like you I don't have a Pi that runs as hot as some reports, and without one it's difficult to form a theory on what the cause is.

yes the IR meter have there issues and you have to know it to get good readings and i have even an very good Fluke 568 there is on the high side of them and i dont use muchs because they crude in eletronics work and it is better to use an IR cam

The Fluke 568 IR meter i am having is having and IR spot of (the number is is IR spot size and the distance from the surface)

Spot 19mm @ 300mm distance

Spot 18mm @ 900mm distance

Spot 42mm @ 1500mm distance

you also has to hold it at an right angle

next time i will do some testing i will take both some IR images and use the IR meter and let you know what it is showing, but in the mean time try look at the images i have posted there is an graf showing the temparatura across the surface of the chip and you can clearly see the edges of the chip and that there is an very tinny hotsport at the center of the chip.

Tooms

it is better to use an IR cam

I'd love one.. I looked at prices. No way can I afford one

The Fluke 568 IR meter i am having

Yeah, that's the one I was looking at, it was the only one I could find that gave a good explanation of the D:S relationship and that was what decided me not to bother getting one - my dodgy sensor stuck to the top center of the IC is likely more accurate

Has anyone found the emissivity coefficients that we should use for the encapsulant on the chip (0.92 has been suggested)?

I've asked a few chip suppliers FAEs and been met with a blank stare!  I guess that's why I still use thermocouples, but they are messy as I always gunk them up with heatsink compound.

Cheers

Pete

Hi

I am using the 0.95e on my Fluke 568 as this is the default one and it is for black plastic

the 568 build in tabel has:

0.93 paint

0.95 plastic

0.93 water

an book i have about IR is having

0.85 Brick, common

0.94 Brick, refractory rough

0.95 electrical tape black plastic

0.92 Glass

0.93 lacquer, bakelite

0.94 paint average oil based

0.94 paper black

0.93 rubber

0.92 tar paper

(I have only listed the values there seems usagbol to this as the list is alot longer..)

So based on this i will say around 0.93-0.95 so a good point will be 0.94e but as other users here is having IR meters and they are very likly fixed at 0.95e so i think it is best to use 0.95 so it is easyer to compire the results there is posted.

Thomas

Seems like a good suggestion - as you say at least we can compare results with some confidence, I think the issue on resolution, spot size is also a complicating factor.  From what I understand you will get the average of the spot size so any real hot spots will be averaged away.

I've been trying to find a IR lens that will give 10mm x 15mm as the total field of view.  Interestingly it gets even more complicated when you look at effective touch temperature and we need a gizmo called a "thermesthesiometer probe" but these are not commercially available as far as I have found - if you find one let me know.

NASA (slightly old but the most recent I could find) have suggested that 45C is tolerable (indefinitely) for polished metal with an effective infinite heat capacity, and obviously a very high thermal conductivity, but this does not play well to our circumstances unless we measure less than that.

So I think there are three issue in this thread:

1) Touch temperature concern.

2) Die temperature and effect on performance.

3) Effect on functionality of USB? (Circumstances yet to be determined)**.

I have not seen any reports that making the suggested mod fixes anything, I'm sure you will let me know if I've missed it.

As always - comments welcome.

Cheers

Pete

Seems like a good suggestion - as you say at least we can compare results with some confidence, I think the issue on resolution, spot size is also a complicating factor.  From what I understand you will get the average of the spot size so any real hot spots will be averaged away.

I've been trying to find a IR lens that will give 10mm x 15mm as the total field of view.  Interestingly it gets even more complicated when you look at effective touch temperature and we need a gizmo called a "thermesthesiometer probe" but these are not commercially available as far as I have found - if you find one let me know.

NASA (slightly old but the most recent I could find) have suggested that 45C is tolerable (indefinitely) for polished metal with an effective infinite heat capacity, and obviously a very high thermal conductivity, but this does not play well to our circumstances unless we measure less than that.

So I think there are three issue in this thread:

1) Touch temperature concern.

2) Die temperature and effect on performance.

3) Effect on functionality of USB? (Circumstances yet to be determined)**.

I have not seen any reports that making the suggested mod fixes anything, I'm sure you will let me know if I've missed it.

As always - comments welcome.

Cheers

Pete