RG1 1.8v regulator

Nice to see you here again, Pete.

My finger is quite toasty now from all the finger tests on my very hot LAN9512.  Looking forward to your input on this!

Morgaine.

I came across a document "Standards for School Premises" at

  http://www.plymouth.gov.uk/standards_for_school_premises_dfes-3.pdf

that says:

   Hot Surfaces   

   83. Some pupils are more at risk than others from hot surfaces. In special

    schools, nursery schools and in teaching accommodation used by nursery

    classes, the surfaces of radiators and exposed pipes located where they

    might be touched by a pupil must not become hotter than 43 degrees C.

This probably isn't directly relevant to electronic devices, but it might suggest

that uncovered electronics with blisteringly hot chips may be considered a

safety hazard in schools.

In California, hot surfaces of 140 degrees F (60 degrees C) are considered

a safety hazard in the workplace.

http://www.dir.ca.gov/oshsb/hot_surfaces_isor.pdf

If you recall our "Finger Contact Survival Time" (:-) testing over in this thread , although initial contact temperature on my Pi was such that pure instinctive body reaction tore the finger away in a fraction of a second to avoid harm, subsequent fingers survived contact for progressively longer periods, indicating that the LAN9512 has low heat capacity and/or high thermal resistivity in its surface material.

Those tests tell me that it's not really a danger in the safety sense.  The temperature is below ignition point for all common materials, and there's not enough of a heat reservoir there to maintain its temperature if coupled to anything that is thermally conducting.  The main danger to humans is probably from the instinctive reaction:  a schoolkid's sudden violent withdrawal of their hand could knock out another kid's eye or break something.

The other thing that those tests tell me is that the main problem doesn't seem to be too much heat being generated but not enough heat being conducted away through the solder connections, because the surface of the device isn't able to conduct nor radiate much heat away at all.

For reference, link to post with thermal image showing the 65.1C peak temperature on LAN9512 .

PS. Because of the low heat capacity and/or high thermal resistivity of the surface material, a thermocouple attached to the surface is likely to indicate a lower temperature than a thermistor.  The thermocouple is entirely metallic and hence very likely to be a good conductor of heat away from the device.  A non-contact measurement like Remy's is best here.

Morgaine.

Yes, I recall the "Finger Contact Survival Time" discussion,

but I'm not sure how relevant it is. As you say, if you pull away

the first finger in a fraction of a second, you can use subsequent

fingers for longer.  But the safety concern is whether the first

finger will get burned if not pulled away in a fraction of a second,

because younger children, older adults, and the disabled are

assumed to have slower reflexes.

Pete,

Here's some additional data.

To hopefully make these reasonably repeatable, here's some detail of the setup I've been using

2012-07-15-wheezy-raspbian.img no firmware/kernel upgrades done.

overscan disabled

1600x1200 Dell 2007FP monitor

all 'idle' readings taken while at a text based login prompt, X has not been started

'playing video' readings taken after running startx and then omxplayer from a terminal to play a 720p h264 mkv file

temperature readings taken with a MCP9803 i2c temperature sensor on top of the lan9512

5v applied via the GPIO header with 16/0.2 cable and I'm arranging that TP1-TP2 reads 5.00v

Ambient, today:

outside 20C

inside 26C

50.3% RH

1005 hPa

at each step I'm giving the board 15mins to reach equlibrium

The blue column at the end is the unloaded voltage reading from RG1 while it's off the board.

Sorry, but I won't be pulling RG1 off that last board, hope you understand why

I have a couple of boards from FN120720xxx FN120722xxx, but as my results are mostly similar I've just picked either end of the range I have along with a couple in the middle.

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.

Catching up after some vacations.

NO IT IS NOT OK to use the VDD18CORE pins as an output supply, they pins are there only to hookup the

decoupling caps for the internal regulator.

Glad you guys had a chance to test the theory, if the Gerbers match the schematics, and the actual PCB match the Gerbers, that's a hardware error on the Rpi, I don't think that there is much more to say.

-J

Hi all and hallo to the forum from Copenhagen Denmark

I have done some testing to try out what your guys saying.

1. using switchmode power
2. the LAN9512 is having an buildin LDO there is haveing higher volt level then the LDO RG1 has and because of this then the LAN9512 LDO is powering the other items there is using the 1V8 and the LDO RG1 is not doing any work.

So i was thinking why not just try add some ebay LM2596 switchmode boards in paralle with the two LDO RG2 3V3 and RG1 1V8 to see if i can get it to use less power and get the LAN9512 to run cooler, so i just add some wires to the RG1 and RG2 and then add the LM2596 with the volt level just an small bit higher then the RG1/LAN9512 and RG2 was showing and by this let the LM2596 do the work..

To the raspberry i connected the buildin network card to the switch and then another usb wireless netcard connected to my wireless network with WPA2 encryption and then an usb webcam to have some things to use power via the network and usb ports.

I then ask the raspberry to take 10000 single images from the webcam with ffmpeg and at the same time i copy some files over the wireless network, this process was running for about 30-45 minutes each time to get the temperature to get stabile

Background rum temperature is 25.5C (measured with Fluke 54II)

The Volt level is measured with an Fluke 8846A

The Amp reading is the reading from the powersuppy (HP 6632B)

This is photo of the setup (and alot other things sorry for the mess)

Here is test 1

Work: Idle mode
Power: Power from buildin RG1 and RG2 LDO
Amp reading = 541.10 mA
RG2 5V0 pin = 4.96150v
RG1 3V3 pin = 3.32753v
RG1 1V8 pin = 1.81029v
Raspi watt =  (4.96150v * 0.54110A) = 2.68466W
temperature - sorry have not taking any images of this

Here is test 2

Work: Idle mode
Power: Power from the onboard LDO and two paralle switchmode LM2596 there is set to 1V8 and 3V3
Amp reading = 443.20 mA
RG2 5V0 pin = 4.98338v
RG1 3V3 pin = 3.35214v
RG1 1V8 pin = 1.84575v
Raspi watt =  (4.98338v * 0.44320) = 2.20863W

Here is an IR images of the PI at this test and the temperature is 49.5C on the LAN9512

Here is test 3

Work: capturing images from webcam and copy data via the wireless network
Power: Power from buildin RG1 and RG2 LDO
Amp reading = 671.51 mA
RG2 5V0 pin = 4.93466v
RG1 3V3 pin = 3.32762v
RG1 1V8 pin = 1.81068v
Raspi watt = (4.93466V * 0.67151A) =  3.31367W

Here is an IR images of the PI at this test and the temperature is 59.2C on the LAN9512

Here is test 4

Work: capturing images from webcam and copy data via the wireless network
Power: Power from the onboard LDO and two paralle switchmode LM2596 there is set to 1V8 and 3V3
Amp reading = 553.19 mA
RG2 5V0 pin = 4.96022v
RG1 3V3 pin = 3.34853v
RG1 1V8 pin = 1.84341v
Raspi watt = (4.96022v * 0.55319A) =  2.74394W

Here is an IR images of the PI at this test and the temperature is 51.3C on the LAN9512

So it seems by add two switchmode power suppy modules for the 3.3V and 1.8V instedt of the LDO then it is using 0.5 watt less power and is running around 8C cooler on the LAN9512.

I guess it will be even better if removing the LDO's from the board and only use the switchmode modules like the ebay LM2596 modules i got from china.

as a side note, i have also bypassed the USB fuses with direct 5v at the fuse on the usb side and i need this to be powering the usb netcard and webcam.

Tooms