nonoti
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The 5V GPIO Power Question

Wed Sep 19, 2018 1:40 pm

I've been reading a lot on the Net about powering the Pi from 5V supplies.

What I would like to know is, if anyone knows the EXACT range of power the 5V GPIO pins can take before the Pi breaks?

I have a situation where I need about 100-200 Pi's in a server room. Ideally, they do not want 5V USB chargers all over the place. There is the possibility that they can supply me with a custom connector to a 5V power rail that can do up to 3A per connection.

However, that rail runs at 5.2V not exactly 5V. Would this damage the Pi on GPIO?

Are there any other options since 2012 where mosts of the posts come from for powering a Pi without relying on Micro USB?

Thx.

B.Goode
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Re: The 5V GPIO Power Question

Wed Sep 19, 2018 3:44 pm

What I would like to know is, if anyone knows the EXACT range of power the 5V GPIO pins can take before the Pi breaks?


Since no model of RPi board has 5 volt GPIO pins the question doesn't arise.

All GPIO pins on an RPi board are rated at 3.3 volts. Engineering being what it is, no doubt there is some latitude above that. But if the designers and marketing people say the limit is 3 3 volts then I for one am not going to put anything different in writing in a public forum.

Note that not all of the pins presented on the 40-way header of an RPi board are GPIO pins.

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mahjongg
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Re: The 5V GPIO Power Question

Wed Sep 19, 2018 3:59 pm

The range of voltages that are acceptable for the PI is any voltage between 4.75V and 5.25V, BECAUSE USB devices need this range! The PI itself is mostly 3V3 powered, and the 3V3 regulator will keep working on a voltage below that 4.65V (that is why the PI can show an undervoltage event without crashing).
Below 4.65V, a voltage monitor will report an undervoltage, by turning off the power LED, and even very short undervoltages trigger an undervoltage icon.
If you put more than 6.0 Volt on the (microUSB) power input an overvoltage protection diode (kind of thyristor, triggered bij more than 6V over it) will short the 5V line on the PI, and this will blow the polyfuse to protect the overvoltage device from burning out.
if you feed 5V directly through the GPIO pin(s) then there is no polyfuse in between to protect the overvoltage diode.

An unrelated issue, is that putting any voltage at any time, however short, of more than the 3.3V supply PLUS one diode forward drop (typically 0.7V) can and will trigger a fatal latch-up event in the silicon near the GPIO driver logic, this event will short out the 3V3 supply to GND (to the substrate of the chip), this will burn out the silicon, which is irreparable, and the damage will spread through the chip if the current is not removed. Read wikipedia "latch up" for an explanation.
In short, the GPIO's are not 5V tolerant!

hippy
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Re: The 5V GPIO Power Question

Wed Sep 19, 2018 4:56 pm

nonoti wrote:
Wed Sep 19, 2018 1:40 pm
There is the possibility that they can supply me with a custom connector to a 5V power rail that can do up to 3A per connection.

However, that rail runs at 5.2V not exactly 5V. Would this damage the Pi on GPIO?
The Pi is officially rated as 5V +/- 5%, 4.75V to 5.25V so your Pi should be okay and being slightly high will help compensate for any losses in the leads connecting from the rail to the Pi.

As to actual maximum voltage you can safely apply to the Pi beyond 5.25V; that depends on the model of Pi you have and what you have connected to it.

To work out what the maximum safe voltage of any Pi model is would require doing a full audit of everything which uses the 5V rail and that isn't easy with only reduced schematics published which don't show all components or connections.

For the Pi Zero and Zero W, with nothing else which uses 5V (HDMI/GPIO/USB) connected at all, the 5V rail appears to only be used by the 3V3 regulator (PAM2306AYPKE) and that should be good for up to 5.5V with an absolute maximum of 6.5V from the datasheet I have. And also good down to 2.5V though you'll be getting 'low power warning' all the time and the official view is that this is a fault condition and will adversely affect your Pi and SD Card.

For other Pi there is a SMBJ5.0A transorb fitted which appears to kick in around 6.4V. One could assume that other components, some not shown on the reduced schematics, would also tolerate that or the protection it offers is mostly illusionary, but it's hard to say.

For example the PMIC on the 3B ( and likely 3B+ ) appears to be good for up to 5.5V with an absolute maximum of 6V, so I imagine that could well be gone before the transorb kicks in.

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mahjongg
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Re: The 5V GPIO Power Question

Fri Sep 21, 2018 5:40 pm

All PI's except the zero have overvoltage protection that will short the 5V line when it raises above 6.0V, so putting 6.5V on it is an absolute no no. :twisted: :roll: The SoC itself is also powered directly from 5V, at least in many models of the PI, if not all of them.

hippy
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Re: The 5V GPIO Power Question

Sat Sep 22, 2018 1:58 am

mahjongg wrote:
Fri Sep 21, 2018 5:40 pm
The SoC itself is also powered directly from 5V, at least in many models of the PI, if not all of them.
Please can you tell us on which Pi models the 5V goes to the SoC.

I was under the impression that no Pi models had 5V to the SoC rather than many.

klricks
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Re: The 5V GPIO Power Question

Sat Sep 22, 2018 2:13 am

hippy wrote:
Sat Sep 22, 2018 1:58 am
mahjongg wrote:
Fri Sep 21, 2018 5:40 pm
The SoC itself is also powered directly from 5V, at least in many models of the PI, if not all of them.
Please can you tell us on which Pi models the 5V goes to the SoC.

I was under the impression that no Pi models had 5V to the SoC rather than many.
The schematic of the RPi1 shows 5V0 connected in 5 places.
https://www.raspberrypi.org/app/uploads ... s-R1.0.pdf
Page 1 grid location 7-E
Unless specified otherwise my response is based on the latest and fully updated Raspbian Stretch w/ Desktop OS.

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Burngate
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Re: The 5V GPIO Power Question

Sat Sep 22, 2018 8:31 am

I was under the impression that, to fit the extra ARM cores on the chip, they removed the power supply bits.
Looking at the Compute Module schematics, 5v doesn't appear to reach the module, so the chip can't require it.

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rpdom
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Re: The 5V GPIO Power Question

Sat Sep 22, 2018 6:37 pm

Burngate wrote:
Sat Sep 22, 2018 8:31 am
I was under the impression that, to fit the extra ARM cores on the chip, they removed the power supply bits.
Looking at the Compute Module schematics, 5v doesn't appear to reach the module, so the chip can't require it.
I think you are right. There used to be internal voltage regulators on the BCM2835 and they are external on the BCM2836/7 (IIRC)

hippy
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Re: The 5V GPIO Power Question

Sat Sep 22, 2018 7:02 pm

klricks wrote:
Sat Sep 22, 2018 2:13 am
hippy wrote:
Sat Sep 22, 2018 1:58 am
I was under the impression that no Pi models had 5V to the SoC rather than many.
The schematic of the RPi1 shows 5V0 connected in 5 places.
https://www.raspberrypi.org/app/uploads ... s-R1.0.pdf
Page 1 grid location 7-E
You are correct; the impression I had was clearly wrong.

Still it would be nice to know which models do have 5V connected to the SoC and which do not.

It would also be nice to have more complete schematics and not have to rely on faulty memory, recollections or impressions, or asking and hoping one gets an answer and hoping one can remember it or find it in the future, but I doubt that is going to happen any time soon.

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Burngate
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Re: The 5V GPIO Power Question

Sun Sep 23, 2018 8:41 am

Yes, it would be nice. I think those in charge understand that. I don't think it'll happen, though

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mahjongg
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Re: The 5V GPIO Power Question

Sun Sep 23, 2018 9:56 pm

their hands are probably bound by contract with the people who are actually making the RPI's. AFAIK that is the case here.

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