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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

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  • I've seen the other threads discussing this subject and I think that what you need is not so much an expert opinion as an informed opinion - from somebody at SMSC who really understands the chip.

    My generalised expert opinion is that (to paraphrase form a 1970's Nat Semi data book) if you operate outside specifications then all bets are cancelled.

    SMSC is in the process of being acquired by Microchip which might well eventually improve the availability of detailed information but the takeover is being held up by legal nonsense (IMHO it's nonsense) so right now I expect they are all worrying about their futures.

     

    I can think of ways to measure the power dissipated by the SMSC chip but you would need a supply of hot and cold Pi's.

     

    Why not try selsinork's mod on a hot Pi and see if it gets better.

     

    Michael Kellett

  • in reply to michaelkellett

    SMSC is in the process of being acquired by Microchip which might well eventually improve the availability of detailed information but the takeover is being held up by legal nonsense

    Seemingly it's now been approved http://www.marketwatch.com/story/smsc-stockholders-approve-merger-with-microchip-2012-07-10

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