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mad-hatter
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Re: Current draw from GPIO pins

Fri Oct 06, 2017 3:44 pm

The site does not explain all the restrictons.
From a document (can't find it now) I read on this site years ago, the maximum curemt that can be drawn from all the pins at the same time should not exceed 55ma, and the current drawn from any one pin should not exceed 16ma. For the moment ignoring the 3.3v line, its the main chip that will be oveloaded, it will die.

gordon77
Posts: 3484
Joined: Sun Aug 05, 2012 3:12 pm

Re: Current draw from GPIO pins

Fri Oct 06, 2017 4:06 pm

mad-hatter wrote:
Fri Oct 06, 2017 3:44 pm
The site does not explain all the restrictons.
From a document (can't find it now) I read on this site years ago, the maximum curemt that can be drawn from all the pins at the same time should not exceed 55ma, and the current drawn from any one pin should not exceed 16ma. For the moment ignoring the 3.3v line, its the main chip that will be oveloaded, it will die.
I believe the 50mA was a restriction due to the 3.3v regulator, which in the latest boards may not be relevant as it's now a 1A regulator. Many references to it in various sites but nothing official l can find.

klricks
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Location: Grants Pass, OR, USA
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Re: Current draw from GPIO pins

Fri Oct 06, 2017 5:14 pm

gordon77 wrote:
Fri Oct 06, 2017 2:56 pm
mad-hatter wrote:
Thu Oct 05, 2017 8:26 pm
This site explains a lot!

https://www.scribd.com/doc/101830961/GPIO-Pads-Control2
Is " The raspberry-Pi 3V3 supply was designed with a maximum current of ~3mA per GPIO pin. If you load each pin with 16mA the total current is 272mA. The 3V3supply will collapse under that " still True on the latest Pi's? Hasn't a larger regulator been added?
There is a larger PS but from what I understand the SOC / GPIO has not changed. There is still a max spec of 50mA across ALL GPIO's combined. So if you want to draw the Max 16mA then only 3 GPIOs could be used. 3*16=48mA. All others must be 0 in that case or else you risk damaging the RPi.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Stretch w/ Desktop OS.

gordon77
Posts: 3484
Joined: Sun Aug 05, 2012 3:12 pm

Re: Current draw from GPIO pins

Fri Oct 06, 2017 5:19 pm

klricks wrote:
Fri Oct 06, 2017 5:14 pm
gordon77 wrote:
Fri Oct 06, 2017 2:56 pm
mad-hatter wrote:
Thu Oct 05, 2017 8:26 pm
This site explains a lot!

https://www.scribd.com/doc/101830961/GPIO-Pads-Control2
Is " The raspberry-Pi 3V3 supply was designed with a maximum current of ~3mA per GPIO pin. If you load each pin with 16mA the total current is 272mA. The 3V3supply will collapse under that " still True on the latest Pi's? Hasn't a larger regulator been added?
There is a larger PS but from what I understand the SOC / GPIO has not changed. There is still a max spec of 50mA across ALL GPIO's combined. So if you want to draw the Max 16mA then only 3 GPIOs could be used. 3*16=48mA. All others must be 0 in that case or else you risk damaging the RPi.
It would be good to get an official view on this 50mA limit, and does it still exist

This site https://raspberrypi.stackexchange.com/q ... imitations

Says "The Pi 3.3V rail is widely claimed to provide 50mA, and each pin 3mA. Gert van Loo explained that these were design values; the circuitry was designed so each of the 17 pins could supply ~3mA, ~51mA in total. This applies to the original Pi A & B; the B+ and later (with 40 pin header), including the Pi Zero, have no such limit."

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