GPIO current rating

Started by Corto, March 06, 2014, 07:17:35 pm

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Corto

Hi everybody,
I'm looking for GPIO maximum current ratings on Olinuxino A20 board but I found this information neither in the board datasheet nor in the processor one (here there is a section dedicated to ratings but in the GPIO current section limits are marked as TBD).
I've seen some users' tutorials to blink led but no one speaks about current limits... any info?  :o

JohnS

If it's not there then about all you can do is contact Allwinner and hope.

They are making noises as if interested in improving their openness so asking may work.

John

dave-at-axon

I can't find the source or sink current but on the A20 Datasheet v1.0 20130227.pdf document from Olimex it shows a column in there with Buffer Strength (mA)and a value for each GPIO as 20

Not knowing if this is sink or source makes the decision a little difficult but I do see that the LED on PH02 is connected as a source but with the 2K2 resistor this is not likely to be drawing any more than 1mA from the GPIO pin.

codifies

While it may seem paranoid, myself I'd either buffer the output (optical buffer chip) or drive only the base of a transistor (obviously with a currently limiting resistor!) that way if something goes wrong with a circuit under development you throw away just a cheap component - at best you might have a SoC without one GPIO pin at worst no SoC...

Corto

Quote from: codifies on March 07, 2014, 04:56:44 pm
While it may seem paranoid, myself I'd either buffer the output (optical buffer chip) or drive only the base of a transistor (obviously with a currently limiting resistor!) that way if something goes wrong with a circuit under development you throw away just a cheap component - at best you might have a SoC without one GPIO pin at worst no SoC...


Of course bufferize the GPIO is always a good idea, usually i prefer this solution too, with a FET transistor to be sure of the low gate driving current... anyway from the Allwinner A20 datasheet that you can find here (https://github.com/OLIMEX/OLINUXINO/blob/master/HARDWARE/A20-PDFs/A20%20Datasheet%20v1.0%2020130227.pdf?raw=true) it seems that the current rating of GPIO pins is of 20 mA (see "buffer-strength" for GPIO pins at pp 13-16)... for me this is an unreasonable value but if they say it...  ::)