Power schematic from AT06068 question

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Gents, First, I have to say that I am not sure if this is the right forum, but I can't find a SAM specific forum, so I though the AVR32 forum would be closest. If not, I would appreciate it if an admin would put it where it needs to be. I have about convenced myself that I need to tackle an ATSAM4E based projected.

 

So, I was going through AT06068: SAM4E Schematic Checklist and looked rather close at the suggested power supply schematic (it is a bit more complex than the ATtiny/ATmegas need) and came across this schematic on page 3 in section 1.1:

 

This is a copy of the 1.2V supply section I put together in Eagle (I couldn't copy the factory schematic). It is exactly the same with all the junctions in exactly the same position. Or look at the original at http://www.atmel.com/images/atmel-42231-sam4e-schematic-checklist_ap-note_at06068.pdf

 

Fundamentally, all that is going on is there is a 1.2V regulator in the chip that takes it's input from the 3.3V VCC, outputs it at VDDOUT so it can be filtered and then brings it back in at VDDCORE and VDDPLL for use. But there are three things in this that make no sense to me:

 

  1. The ground connection goes from the left side of the top capacitor all the way around the VDDPLL pin! And it is NOT connected to ground at any point
  2. The 100nF capacitor on the bottom left is completely shorted out!
  3. What is the 10uH inductor doing? I would expect it to be filtering the power going into VDDPLL, but how is it doing that in this schematic?

 

I've also looked at the ATSAM4E-PRO board schematics and I'm having a hard time finding anything like this in that schematic. This is how I would expect the schematic to be drawn based on what I THINK it is doing:

In my schematic, the first three capacitors provide filtering and storage for the 1.2V supply. The 10uH inductor filters power going into VDDPLL and the 4.7uF capacitor provides storage for VDDPLL. Any suggestions on what is actually going on with the factory schematic? Thanks!

 

Clint

Last Edited: Sat. Sep 6, 2014 - 02:00 AM
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LOL !
Not content with making one stuffup in that checklist document, the author repeats the same arrangement in another diagram, and then for extra bonus points shorts the VDDCORE to ground in a third diagram. !
Maybe Atmel needs some internal proofreaders.

Personally., I'd use the basic layout from the SAM4E datasheet and augment it with what is sensible from the checklist.
The datasheet doesn't mention inductors anywhere for VDDPLL but sortof implies it when it specifies the maximum allowed ripple on VDDPLL.
(But what to believe ?, the datasheet says VDDPLL max ripple is 30mV but the checklist says 10mV and there are no inductors on the VDDPLL line of the SAM4E Xplained-Pro board)
A 'hedge-your-bet' idea would be to put a footprint for an inductor but populate it with a zero-ohm resistor initially.

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RRRoamer wrote:
I can't find a SAM specific forum

It's here: http://www.at91.com/

SAM4 specifically: http://www.at91.com/discussions/...

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Thanks!  I recently came across that forum but didn't realize it was related to avrfreaks.

 

awneil wrote:

 

RRRoamer wrote:

I can't find a SAM specific forum

 

It's here: http://www.at91.com/

SAM4 specifically: http://www.at91.com/discussions/viewforum.php/f,29/sid,2d8b524bae724a0a2cd49d9884a41f36.html

 

Clint

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So it's nice to know that I haven't secretly taken up smoking crack...

 

mikech wrote:

LOL !
Not content with making one stuffup in that checklist document, the author repeats the same arrangement in another diagram, and then for extra bonus points shorts the VDDCORE to ground in a third diagram. !
Maybe Atmel needs some internal proofreaders.

Personally., I'd use the basic layout from the SAM4E datasheet and augment it with what is sensible from the checklist.
The datasheet doesn't mention inductors anywhere for VDDPLL but sortof implies it when it specifies the maximum allowed ripple on VDDPLL.
(But what to believe ?, the datasheet says VDDPLL max ripple is 30mV but the checklist says 10mV and there are no inductors on the VDDPLL line of the SAM4E Xplained-Pro board)
A 'hedge-your-bet' idea would be to put a footprint for an inductor but populate it with a zero-ohm resistor initially.

 

Clint