2 replies to this topic

[Tim Mattison]

The Netduino Plus specs indicate the following in the "Power" section: max current: 8 mA per pin digital pins 2, 3, 7: 16 mA per pin analog pins 0-3: 2 mA per pin microcontroller max current: 200 mA total Does this mean that the max current for digital pins, other than 2, 3, and 7, is 8mA and for 2, 3, and 7 it is 16mA? Do these limits refer to current that it can sink, source, or both? For analog pins it must be the maximum sink current because they're inputs but for the digital pins I just want to be sure.

[Mario Vernari]

The microcontroller is based on the HCMOS technology. This approach uses a couple of mosfets (P and N-channel) in push-pull mode, in a systematic way. In such a context, there's no difference on the maximum current as source or as sink: they're equivalent. Whereas the pin is set (or can be) as an input, you can't talk about "source", nor "sink" current. It's called "leakage current", and it's related to the very small drain of electrons into the input itself. If you read the specs, that's current is typically around 20-40 nA, but may raise to x10 as the temperature gets higher. This leakage current is *roughly* equivalent to a resistor going to ground. Its value is approximately Vinput / Ileak, so several tens of MegOhms. Please, note that "small drain of electrons" is just for comparison with an ordinary current flowing through a led or else. A little 20nA flow means an average of one billion (1E12) electrons per second. Cheers

[Tim Mattison]

Thanks for the fast reply, it makes a lot more sense now. I'm no EE (obviously!) but this will do for my purposes.