gregeric
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Joined: Mon Nov 28, 2011 10:08 am

Re: RPi2 USB current output specifications

Sun Feb 21, 2016 5:34 pm

@davidcotton the PAM2306 reg has recommended max 5.5V, absolute max 6.5V, same goes for the AP2553 current switch. The soc will continue to see 3V3 & 1V8 on its supply rails.

On the HDMI side the AP2551 has 5.2V/6.5V specs., but it trips (cuts power) at 5.3V so if that is exceeded the display may go off, nothing worse than that.

Is there anything else to consider?

MrNice
Posts: 72
Joined: Thu Oct 17, 2013 10:18 am

Re: RPi2 USB current output specifications

Sun Feb 21, 2016 7:14 pm

Done and working/playing fine
With models A and B results are the same. I'd guess the difference is only the plug (USA, Australia)
I didn't try model C as you says voltage is too high

Code: Select all

With PSU Samsung ETA-U90EBE	(Model B)
1m Thin cable (no ref)
Load	A@5V	PP1-PP5	PP1-PP35	USB pin	USB outside connector
0	0	5.16	5.15	5.10	5.10
20	.250	5.17	5.15	5.07	5.06
10	.500	5.17	5.16	5.02	5.00
5	1	5.14	5.08	4.90	4.86
3.33	1.50	5.15	5.07	4.78	4.58

1m 23AWGx2C 30AWGx2C cable
0	0	5.16	5.15	5.10	5.10
10	.500	5.15	5.12	5.01	4.94
5	1	5.13	5.07	4.89	4.74
3.33	1.50	5.12	5.05	4.79	4.56

Nota: 82Kohms//R4
I noticed when moving USB connector it could change the voltage for 20-40mV
No noticeable difference with thin or AWG23 cable, the connector quality is more important.
The voltage loss with load is catch up by the PSU over-voltage and results of an almost constant voltage at PP5

Hope this will help

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davidcoton
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Re: RPi2 USB current output specifications

Sun Feb 21, 2016 7:46 pm

gregeric wrote:@davidcoton the PAM2306 reg has recommended max 5.5V, absolute max 6.5V, same goes for the AP2553 current switch. The soc will continue to see 3V3 & 1V8 on its supply rails.

On the HDMI side the AP2551 has 5.2V/6.5V specs., but it trips (cuts power) at 5.3V so if that is exceeded the display may go off, nothing worse than that.

Is there anything else to consider?
Well, you may be right. While 5V +/- 5% has been widely quoted here, I can't find an authoritative source for that limit on this site. However, I prefer to be conservative in my own engineering, and I won't recommend anything to others that I wouldn't do myself. If RPF publish a higher voltage limit, I'm happy with that. Until then I will stick to 5.25V as the maximum recommended input. (Note also the possible consequences to external 5V devices connected to the Pi, which may not tolerate in excess of 5.25V.)
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gregeric
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Joined: Mon Nov 28, 2011 10:08 am

Re: RPi2 USB current output specifications

Sun Feb 21, 2016 8:08 pm

Yes I had overlooked downstream USB devices, but given the last set of measurements from MrNice of those PSUs in service, including USBvbus , no concerns there either.

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GTR2Fan
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Re: RPi2 USB current output specifications

Sun Feb 21, 2016 8:12 pm

davidcoton wrote:While 5V +/- 5% has been widely quoted here, I can't find an authoritative source for that limit on this site.
That's the official certified USB industry-standard specified voltage range for pre-USB3.0 interfaces.

It's actually specified as 5.00V +/-0.25V, so it makes perfect sense to not stray outside these limits, especially when other USB devices are attached to the Pi.
Pi2B Mini-PC/Media Centre: ARM=1GHz (+3), Core=500MHz, v3d=500MHz, h264=333MHz, RAM=DDR2-1200 (+6/+4/+4+schmoo). Sandisk Ultra HC-I 32GB microSD card on '50=100' OCed slot (42MB/s read) running Raspbian/KODI16, Seagate 3.5" 1.5TB HDD mass storage.

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davidcoton
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Re: RPi2 USB current output specifications

Sun Feb 21, 2016 8:19 pm

GTR2Fan wrote:
davidcoton wrote:While 5V +/- 5% has been widely quoted here, I can't find an authoritative source for that limit on this site.
That's the official certified USB industry-standard specified voltage range for pre-USB3.0 interfaces.

It's actually specified as 5.00V +/-0.25V, so it makes perfect sense to not stray outside these limits, especially when other USB devices are attached to the Pi.
Thanks. It's nice to know that my intuitive conservative engineering got it right this time! Interesting too that the voltage spec uses absolute limits rather than a percentage tolerance.
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