RG1 1.8v regulator

I wasn't so sure about their complete independence inside the LAN9512 when looking at the datasheet.

The VDD18ETHPLL and VDD18USBPLL lines are also connected to L3 which is specc'd at 100MHz so it seems strongly related to dynamic PLL operation (L3 is isolating ETH and USB sections from each other for RF, similar to L4 on the 3V3 side), and neither of those PLL lines has a tank cap like the 4.7uF on the 1V8CORE lines, so it doesn't seem to be caring about low-frequency stability.  That suggested to me that the PLL's 1.8V may actually be affected by the core 1V8 LDO, if not directly as a source (which seems unlikely since it's fed from 3V3) then at least indirectly through core logic.

When SMSC go to all the trouble of inductively isolating the USB and ETH sections of both their 3V3 and 1V8 LDOs, it's easy to imagine that they're not too impressed when their 1V8CORE pins are coupled to something foreign.

There are also some additional bits of information to consider based on reports of problems with Ethernet and the X1 crystal. If there are indeed power issues on the SMSC core that may produce unstable operation of the internal clock signals and ethernet is particularly picky about clock jitter and shape which may get the part to operate out of the IEEE specs. I've seen this problem with some Ethernet controllers/PHYs where temperature produces too much drift on the crystal/oscillator and the ethernet link is lost.

And who said that the parts on the R-pi are rated to operate at 120C ?

The PoP RAM chip on top of the SoC is rated for Commercial temp ranges, it varies from mobile to normal applications but it does not exceed 95C.

There is a lot of clueless folks at the R-Pi forum contributing wrong information to the already existing confusion.

-J

There's a dedicated thread now in the other forum.

http://www.raspberrypi.org/phpBB3/viewtopic.php?f=29&t=14489

Love the classical cryptyc response from RPF minions ...

-J

coder27 wrote:

 

There's a dedicated thread now in the other forum.

 

http://www.raspberrypi.org/phpBB3/viewtopic.php?f=29&t=14489

From that thread:

JamesH wrote, on the RPF forum:

 

Cannot say much about this, except that the Foundation are aware

of the problem and are working to rectify it.

And why exactly can the Foundation not say much about it?

This is a board intended for technical education, not a secret product hiding trade secrets for commercial advantage.  Why are essential items of information like the gerbers hidden?  Why are problems hidden?  Why are solutions hidden?  Why are future plans hidden?

I think I can summarize the questions more succinctly, if less politely:

Why is the Foundation full of it?

Morgaine.

There is a lot of clueless folks at the R-Pi forum contributing wrong information to the already existing confusion.

+1

Fairly clear that a lot of them are consumer level and are just blundering around in the dark..  If you dare to comment on them being clueless you just get shot down. Not worth the effort anymore IMHO.

selsinork wrote:

 

Fairly clear that a lot of them are consumer level and are just blundering around in the dark..  If you dare to comment on them being clueless you just get shot down. Not worth the effort anymore IMHO.

That's a comment that applies far more widely than just to RPF's non-technical followers.  Unfortunately humanity is largely broken, the far greater proportion of it not being able nor willing to be rational.  Spok would weep in sympathy.

It's instinctive for engineers to want to fix things, so when we see broken people, we occasionally try to convince them of their errors through clear factual and logical argument, but more often than not that's a doomed exercise since they "lack the hooks" for it to work.  More likely to succeed is appealing to emotion or self-interest, but those are not engineering methods and do not taste good to the engineering palate.  Also, most of us are not good at them.

I think it boils down to "Choose your fights wisely".  We can't fix the clueless millions, but we can focus on RPF as a public entity which is legally accountable for what it does, and we can focus on product which does have to conform to standards when claimed and does have to operate as advertised.  Those things do provide us with hooks so we're not totally powerless to fix what is wrong.

But no, we can't fix the clueless followers.  At best, only their descendents might be fixable through education.

Morgaine.

I just did some digging in the NCP1117 data sheet (ONsemi version).

RG1 is an NCP1117-1v8 fixed linear LDO regulator.  We have suggested that if RG1's regulation voltage Vreg is greater than IC3's (LAN9512) internal Vreg, then RG1 will supply 1.8V current instead of IC3, reducing IC3's power consumption.

The NCP1117 has a "adjustable output" version which sets Vreg using external resistors instead of internal resistors like the NCP1117-1v8.  In addition, you can adjust Vreg of the "fixed" version with an external resistor plus a stabilization capacitor.  Take a look at Figures 31 and 32.  In Figure 31, a 50 Ohm resistor between the NCP1117's GND pin and circuit GND shifts its output by 300 mV.  Figure 32 uses a variable resistor.  Shifting RG1's Vreg up by 90 mV (+5%) might do a nice job of cooling down IC3 -- probably a 15 Ohm resistor.

Figure 31 also confirms that if two NCP1117's are connected in parallel, the LDO with higher Vreg does switch off the LDO with lower Vreg.

I usually read these posts with interest to keep abreast of discoveries of potential issues with the R-Pi but these last few posts have bugged me because they are as disappointing to read as the gushing exultations of fanbois.

The problem with contradicting peoples' beliefs and emotions (which is one outcome of hype) is that, in general, "rationality" of the Spock-kind comes over as being pompous self-righteousness, no matter how correct someone may be (with some egos confusing "usually correct" with "infallibly correct").

Convincing people relies on an aspect of humanity which most technical types I've dealt with seem to lack and that aspect is empathy

This means having to sit with the non-tehnical person in their viewpoint of the situation (because there was a time when you weren't an expert either), then guide them on a short-ish journey of self-discovery.

In my own job (Industrial Instrument Maker/Repairer) if you had no such empathy, you would continue to be called to jobs which the 'technically unaware' had 'fixed' themselves... like the truckie who would get a $10k tanker-decanting control system to work by bashing it with a rock, but I digress...

In addition, regardless of how well you make an argument technically, if the points you raise do not affect the majority of people in the pursuit of whatever endeavours they choose with the device, then you'll only be arguing for the sake of hearing your own voice and having nothing better to do.

Let's say that as a result of this endeavour to bring down the ruthless RPF Oppressor that there is some degree of success and the RPF folds as a result of it?

Would you be satisfied knowing that you've been proven technically correct whilst successfully preventing the device from reaching those people whom the device may work within their requirements or that the device now costs $70.00 before adding the power supply, etc?

How can you hope to educate the technically-unwashed when your war has made a casualty of the only potential path they have to understanding in the near future and you've offered no tangible and immediately available alternative for equivalent cost?

I'd like to see less posts of the "For the glorious struggle against the oppressors of freedom that are the RPF" type and more of the "These are my findings and in day-to-day operations of type x under conditions y, then the device may fail", the likelihood of this happening (MTBF) and also  what the wider effect this has, bearing in mind that the investigations presented thus far cannot be demonstrated as being representative of a large sample of all devices produced.

If you want rational, be wary that you don't become irrational in your efforts to secure it.

Also remember that there's a difference between fit-for-purpose and a technically-perfect design, and that these states are mutually exclusive in the minds of most techie types, if the former exists at all.

Please provide an URL to the datasheet you found. I searched for NCP1117 and

found: http://unihedron.com/projects/sqm-le/PDFspecs/NCP1117-D.PDF as the first hit. That one doesn't have figures 31 and 32. (but you're referring to figures 28 and 29 in that datasheet).