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)
