eijia
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Is the voltage at the USB hub regulated on the RPi3B?

Fri Sep 14, 2018 10:12 pm

Using the RPI3b.

I know that it should be 5V, but is it directly connected to the source?

If the source goes to 5.5V, will the USB hub on the Pi also provide 5.5V or is it regulated down to 5V?

klricks
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Re: Is the voltage at the USB hub regulated on the RPi3B?

Fri Sep 14, 2018 11:08 pm

eijia wrote:
Fri Sep 14, 2018 10:12 pm
Using the RPI3b.

I know that it should be 5V, but is it directly connected to the source?

If the source goes to 5.5V, will the USB hub on the Pi also provide 5.5V or is it regulated down to 5V?
There is no 5V regulator. There will be a small voltage drop across the 'polyfuse' and the USB power controller chip.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Stretch w/ Desktop OS.

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davidcoton
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Re: Is the voltage at the USB hub regulated on the RPi3B?

Sat Sep 15, 2018 9:50 am

eijia wrote:
Fri Sep 14, 2018 10:12 pm
Using the RPI3b.

I know that it should be 5V, but is it directly connected to the source?

If the source goes to 5.5V, will the USB hub on the Pi also provide 5.5V or is it regulated down to 5V?
It is directly connected. The spec limit for voltage input is 5V +/- 0.25V, so 5.5V is out of spec.
AIUI the spec is derived from the USB voltage spec for this reason.
"Thanks for saving my life." See https://www.raspberrypi.org/forums/viewtopic.php?p=1327656#p1327656
“Raspberry Pi is a trademark of the Raspberry Pi Foundation”

hippy
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Location: UK

Re: Is the voltage at the USB hub regulated on the RPi3B?

Sat Sep 15, 2018 6:25 pm

davidcoton wrote:
Sat Sep 15, 2018 9:50 am
It is directly connected.
Not to the '5V source' it isn't as klricks notes. It goes through the polyfuse and 'ideal diode' if powered through the micro-USB, and goes through the USB power control chip as well, even if power is sourced via the GPIO connector.

But it is pretty much 'what goes in is what comes out', not regulated AFAIK but we don't have a published circuit diagram which shows the USB power control chip and I have no idea what it's doing or what its spec is.

And yes, I know I am being pedantic, but "directly connected" suggests something which isn't true which could bite someone if they took that at face value. It is directly connected on the Zeroes.

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davidcoton
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Re: Is the voltage at the USB hub regulated on the RPi3B?

Sat Sep 15, 2018 9:55 pm

hippy wrote:
Sat Sep 15, 2018 6:25 pm
davidcoton wrote:
Sat Sep 15, 2018 9:50 am
It is directly connected.
Not to the '5V source' it isn't as klricks notes. It goes through the polyfuse and 'ideal diode' if powered through the micro-USB, and goes through the USB power control chip as well, even if power is sourced via the GPIO connector.

But it is pretty much 'what goes in is what comes out', not regulated AFAIK but we don't have a published circuit diagram which shows the USB power control chip and I have no idea what it's doing or what its spec is.

And yes, I know I am being pedantic, but "directly connected" suggests something which isn't true which could bite someone if they took that at face value. It is directly connected on the Zeroes.
I'll give you half marks ;) The question is about the on-board hub, which itself contains the USB power protection/switching elements. So in that sense the hub is directly connected. I concede that the polyfuse intervenes, but that is on overcurrent device, not a regulator. The voltage drop should be negligible, apart from a severe overcurrent fault. So not relevant to the question.
There is always a problem about full answers vs sufficient answers. You earn half marks only because I strayed too far from full. :lol:
"Thanks for saving my life." See https://www.raspberrypi.org/forums/viewtopic.php?p=1327656#p1327656
“Raspberry Pi is a trademark of the Raspberry Pi Foundation”

hippy
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Re: Is the voltage at the USB hub regulated on the RPi3B?

Sat Sep 15, 2018 10:12 pm

davidcoton wrote:
Sat Sep 15, 2018 9:55 pm
I'll give you half marks ;) The question is about the on-board hub, which itself contains the USB power protection/switching elements. So in that sense the hub is directly connected.
I'll agree there, your are right. To push it to Pedantic Level 11 I could say I believe the protection / switching is external to the hub chip and between that and the sockets. But I think we've hit the end of that road, and it wouldn't invalidate what you have said :P

klricks
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Re: Is the voltage at the USB hub regulated on the RPi3B?

Sat Sep 15, 2018 11:21 pm

hippy wrote:
Sat Sep 15, 2018 6:25 pm
davidcoton wrote:
Sat Sep 15, 2018 9:50 am
It is directly connected.
Not to the '5V source' it isn't as klricks notes. It goes through the polyfuse and 'ideal diode' if powered through the micro-USB, and goes through the USB power control chip as well, even if power is sourced via the GPIO connector.

But it is pretty much 'what goes in is what comes out', not regulated AFAIK but we don't have a published circuit diagram which shows the USB power control chip and I have no idea what it's doing or what its spec is.

And yes, I know I am being pedantic, but "directly connected" suggests something which isn't true which could bite someone if they took that at face value. It is directly connected on the Zeroes.
I believe the 'ideal diode' is not included on the RPi3B+ and the USB power control is U13 which on the 3B+ is the 6 pin chip next to the PoE connector: https://www.diodes.com/assets/Datasheets/AP255x.pdf
Unless specified otherwise my response is based on the latest and fully updated Raspbian Stretch w/ Desktop OS.

hippy
Posts: 3570
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: Is the voltage at the USB hub regulated on the RPi3B?

Sun Sep 16, 2018 6:22 pm

klricks wrote:
Sat Sep 15, 2018 11:21 pm
I believe the 'ideal diode' is not included on the RPi3B+
That appears to be correct from the reduced schematics but the OP indicates they have a 3B.

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