Here is a wiring diagram of the pin from the datasheet. From this picture it is not visible that it is possible to draw current from such a pin, e.g. 40mA. Going from the pin to the right we have a pullup resistor through which, I don't think it is possible to draw 40mA, and further to the right we have flip-flops through which it also does not seem possible to draw such current. So what is it like? Can anyone explain this.
The left pointing triangle in the centre of the diagram is the source of the current.
The current is not limited to 40mA by the circuit above, you have to ensure that your load doesn't draw more than 40mA.
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If you read the description, you will see that it is a functional diagram of an I/O port. You can’t infer anything about output current or voltage from that diagram.
Microchip does not publish the actual schematic but I am sure that it is a typical CMOS totem pole output that uses a PMOS and NMOS transistor. The PMOS sources the current and the NMOS sinks the current.
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Thank you for the fast reply. You are right, I think, but to be frank, I am not sure to the end.
40 mA is only example value, I know that above this value pin can be damaged.
I moved your topic to an appropriate forum category @zom123.
In the future, please take some time to pick the forum category that best suits the subject of your topic. There is an "About the _____ category" topic at the top of each category that explains its purpose.
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If you think 39.9mA is safe and 40.1mA will kill something then you are mistaken. Maybe you'll get away with 45mA, maybe even 50mA, who knows? Unless you are doing it to experiment I suggest you stay away from even getting close to 40mA. I'd regard 20mA as the safe limit, and prefer to stay under that. All 40mA means is that Microchip will guarantee that as the absolute maximum safe current, but getting close to it, let alone exceeding it, is not wise.
Correct, but that's not what pullup resistors are for, they are to hold the pin high when used as an input, which as nothing to do with what happens when the pins is used as an output.
Also you should rake into account that there are max. currents for all outputs together.. .
If you take 40mA per pin, it is quite easy to go beyond the max. sum...
There may be a misconception here. There is no threshold for the current to be safe / not safe. The issue is thermal stress on the processor "chip". A "safe" current also depends on the load on the adjacent pin, the sum of the loads on all the pins, the ambient temperature, how well the chip can get rid of the heat etc.
In general, the hotter the "chip" the shorter the life.
And above 200 degC the life all of a sudden becomes very short....
Maybe, the real killer is thermal cycling. If the high power goes on and off slow enough for the die to change temperature a significant amount, the life ill shorten even more.
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