drawing max current from PIC

[Guest sstandfast]

Hey guys, I have a quick question about application for you.  In my project I am wanting to use a logic controlled analog switch as an input selector and I have a question about interfacing it with a PIC.

On the logic input pin of the switch, according to the data sheet the maximum input current that this can handle is 0.5uA which means that with the 5V supplied by the microcontroller the switch has to have an internal resistance of at least 10MEG between the logic input and GND.  Since this information is not included in the data sheet and also because I have not been able to measure this resistance I am leary about tieing the pins together directly.  One possible solution I have came up with is to tie a 200 Ohm resistor from the node to DGND.  Only the thing is if I do this then the PIC will be supplying its maximum amount of current all the time.  Which brings me to my question; is it ok to draw max current from the PIC for periods of time without damaging it?

Thanks,

Shawn

[TK.]

Hi Shawn,

so long as you are using logic ICs which are supplied with the same voltage, resistors between the outputs and inputs are not required. The current consumption of the input is 0.5uA, this means that you could (theoretically) drive up to 50.000 inputs with one PIC output. Ok, in practice the number is much lower due to capacitancies, but in fact with such a low consumption you don't have to take care about the max current

Best Regards, Thorsten.

[Guest sstandfast]

Thanks Thorsten,

So what you are saying is that so long as both the PIC and the logic switch are driven by the same power source then I do not have to worry about either the internal resistance of the logic switch or the overloading of the logic input pin on the switch with too much current.  This makes things a little simpler.  I was just worried that the switch would be able to draw more current through the input pin than it is able to tolerate and would burn itself out, but I guess I don’t have to.

On a side note, I feel that I owe everybody on this forum, especially you Thorsten, both a thank you and an apology.  I would like to thank everybody for being both supportive and very helpful to me even though I feel I may ask some pretty unintelligent and/or obvious questions sometimes.  Since I am pretty much learning about electronics as I go along, I haven't even taken an introductory course to electronics, the constructive comments and explanations given by the people on this thread have been more than an asset for me.

I feel I owe everyone an apology because even though I know this forum is for people building MIDI boxes, I continue to ask off topic questions and I apologize for this.  My hope is that sometime in the future, after I gain some practical experience working with electronics, that I might be able to tackle one of these infamous MIDI "Beasts" that Thorsten has created.  Until then, I hope that I can continue to draw upon this forum as a resource and sounding board whenever I have a question and/or concern.  Keep up the good work guys!

Thanks,

Shawn