output impedance

[qtommer]

hi i would like if anyone knows how much the output resistance of a single I/O pin of the PIC 16F series ?
apparently CMOS is high input impedance and low output impedance but I want to know exactly how much Thanks!!!

 

[ronsimpson]

It is in the data sheet under DC I/O pins. It depends on VCC voltage. Some pins are lower than other. Some pull down very hard.

 

[Nigel Goodwin]

It's also not something you need to know, they specify maximum current that can be sunk or sourced, and that's all you need.

Why do you think you need to know the impedance?.

 

[qtommer]

hi thanks for replying
I was just wondering that if I were to connect a pin to control the base of a resistor, to be realllly precise about the base resistance that controls the base current, that I add the internal resistance together with the base resistance and from there obtaining the precise base current. Does my assumption hold correct? Thanks

 

[Nigel Goodwin]

hi thanks for replying
I was just wondering that if I were to connect a pin to control the base of a resistor, to be realllly precise about the base resistance that controls the base current, that I add the internal resistance together with the base resistance and from there obtaining the precise base current. Does my assumption hold correct? Thanks

No it doesn't - and there's no point been 'really precise' about the value of the base resistor.

You simply dump as much current in the base as you can, in order to ensure it's saturated - the PIC can supply about 30mA per pin - but it's really VERY, VERY non-critical (about 150 ohms is as low as you should go). It really depends on the exact application, but there's no precise calculation required.

 

[MikeMl]

Not quite. You need to look at the Ipin vs Vpin diagrams (one for Voh and one for Vol) on the data sheet of the PIC. The I/V curve is non-linear, so trying to call it an "output impedance" is not appropriate.