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In Reply to: RE: Being one who posted by AbeCollins on February 17, 2017 at 12:50:30
If you don't use GPIO its going to sound like crap....because as you already pointed out, you will still be using the Internal Regulators.Didn't mean to throw you under the Bus....:)
Edits: 02/17/17Follow Ups:
No bus! Please no bus! Nah, I didn't see it that way.What puzzles me though is even if you go thru the GPIO, various components on the RPi still require 1.8V, 2.5V, 3.3V, and 5V. So those voltages must come from somewhere and I would guess that those onboard regulators are still in play. That is, unless you provide all of those voltages separately yourself via GPIO. I haven't looked at the GPIO schematic so I really don't know.
Edits: 02/17/17 02/17/17 02/17/17
You are right, many different voltages at play.
From what I gather, the regulation occurs at the main miniUSB input and voltages are supplied without further regulation. It would not make sense to regulate the incoming and then regulate the regulated again for each step. This would not only add cost but create a redundant step.
Again from reading the manual and other literature about the RPI all regulation is bypass when the GPIO is used. Therefore, there is a Warning to Not Use GPIO unless the PS is regulated otherwise you might damage the unit.
Don't worry about the Bus, I'm sure you have been run over plenty of times and know how to get out of the way by now.
:-)
From what I saw in the schematic the RPi takes in regulated 5VDC to power some components but the others are powered by additional regulators that take the 5VDC and regulate it down to 1.8V, 2.5V, and 3.3V. So there are three onboard regulators.
This is a partial schematic from an older RPi but I suspect the newer ones also require multiple voltages.
Thanks for the schematic, now we can know "For Sure" what other regulators are being used. See below data sheets from the manufacture.
Spoiler Alert: Looks like they are Linear Regulated.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The NCP1117 series are low dropout (LDO) positive linear voltage regulators that are capable of providing an output current that is in excess of 1.0 A with a maximum dropout voltage of 1.2 V at 800 mA over temperature. This series contains eight fixed output voltages of 1.5 V, 1.8 V, 2.0 V, 2.5 V, 2.85 V, 3.3 V, 5.0 V, and 12 V that have no minimum load requirement to maintain regulation. Also included is an adjustable output version that can be programmed from 1.25 V to 18.8 V with two external resistors. On chip trimming adjusts the reference/output voltage to within +/- 1.0% accuracy. Internal protection features consist of output current limiting, safe operating area compensation, and thermal shutdown. The NCP1117 series can operate with up to 20 V input. Devices are available in SOT223 and DPAK packages.
Line Regulation for 3.3 V = 0.8mV or 0.0008V
http://www.onsemi.com/PowerSolutions/product.do?id=NCP1117
http://www.onsemi.com/pub_link/Collateral/NCP1117-D.PDF
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
LP29808.1 Application Information
The LP2980-N is a linear voltage regulator operating from 2.1 V to 16 V on the input and regulates voltages
between 2.5 V to 5 V with 0.5% accuracy and 50-mA maximum output current. Efficiency is defined by the ratio
of output voltage to input voltage because the LP2980-N is a linear voltage regulator.Line Regulation for ≤ 16 V = 0.7mV or 0.0007V
http://www.ti.com/lit/ds/symlink/lp2980-n.pdf
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`
Edits: 02/18/17 02/18/17
No spoiler, I realized they were all three terminal linear regulators per the schematic. But I thought your goal was to bypass all the onboard regulators with something better.
Edits: 02/18/17
how relevant some specs are.Usually if some is good then more is better...we don't consider how much is enough, just more is better.
Same thing for specs, sure I've seen 0.003mV regulators. Even iFi specs rate the voltage as +/-.5V....which is actually much worse than the RPI internal regulator variance. But still, even if you use a 0.0000001mv regulator how much does the ARM processor pollute the whole system?
Pretty much, you can't obsess over one factor and ignore the whole chain. The RPI's regulators are but one factor in a chain of many many variables.
IMO, better to start with the low hanging fruit. Then work you way systematically and logically into other variables that produce the greatest effect on the whole system.
Edits: 02/18/17
That was my goal.
I bypass the switching with something better.
The ones left are linear with 0.8mV and 0.7mv regulation. I can live with that...that is to say my ears are not complaining.
They do have better regulators but I'm not trying to solder something that small...
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