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expert opinion needed on Raspberry Pi power issue

Former Member

The Raspberry Pi has an LDO voltage regulator to produce 1.8v. 

However, a thermal image of the board, see post #6 on this thread:

http://www.element14.com/community/thread/18991

shows that this regulator, RG1, (the largest blue rectangle in the

upper-left quadrant) to be cool, while the hottest chip is the LAN chip

(SMSC LAN9512).  It turns out that the LAN chip has an internal

1.8v regulator, which user jamodio noticed is apparently connected

to the 1.8v power plane where it normally would be connected

only to decoupling capacitors, not the power plane.  User selsinork

verified that if RG1 is removed completely from the board, the

board still works, apparently drawing all its 1.8v power through

the LAN chip.  User beetem, who first noticed the cool RG1,

has commented on possible problems with having two LDO

regulators operating in parallel like this.

 

So is this really a problem?  If so, how serious?  Is there an

explanation for why some boards run significantly hotter than

others?  How to get element14's attention?

 

The latest thread is here:

http://www.element14.com/community/thread/19236?start=15&tstart=0

 

SMSC datasheet, showing VDD18CORE connected to decoupling

capacitors in Figure 2.2, page 16:

http://www.smsc.com/media/Downloads_Public/Data_Sheets/9512.pdf

 

Raspberry Pi Schematic 1.0, where top left of page 3 of 5 shows VDD18CORE

connected to +1.8v in addition to decoupling capacitors.

http://www.element14.com/community/solutions/5952

 

jamodio's original 10 June 2010 report (post #137)

http://www.element14.com/community/message/53280

Parents

  •  

    Mike Powell pinged me this thread directly and asked if I could respond, first apologies dropping of the radar (is it really that long!).  I have been looking at board bugs and this one is on my list, notes in my lab so more tomorrow.

     

    All - it would be really helpful if you could call out your serial numbers, it would allow me to find one in my stash with (hopefully) the same batch of parts, then we can get test aligned.

    Pete

     

  • in reply to Former Member

    PeteL wrote:

     

     

     

    Mike Powell pinged me this thread directly and asked if I could respond, first apologies dropping of the radar (is it really that long!).  I have been looking at board bugs and this one is on my list, notes in my lab so more tomorrow.

     

     

     

     

    It would be extremely interesting to see what else is on the "list"

     

    -J

Reply
  • in reply to Former Member

    PeteL wrote:

     

     

     

    Mike Powell pinged me this thread directly and asked if I could respond, first apologies dropping of the radar (is it really that long!).  I have been looking at board bugs and this one is on my list, notes in my lab so more tomorrow.

     

     

     

     

    It would be extremely interesting to see what else is on the "list"

     

    -J

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