Hi
I'm having a µC that is able to sink/source 3mA.
I have 2 inputs and 2 outputs that must be connected to some external devices through optocouplers that must be pretty fast.
First I thought of a 74OL6000 from fairchild, but they seems to be obsolete, or at least I can't find them anywhere. Then i looked through Fairchilds homepage for another one, that would be easier the get. The one i found was FOD0710 (12,5Mbit/s).
1.
Now I'm not sure if I need to connect any resistors on any side of optocouplers. I don't know, when controlling the output, and driving it low if the output should sink any current(for driving the optocoupler LED) or if the current runs from VCC to GND of the optocoupler, and no (mentionable) current runs through the output pin to GND.
2.
And for the inputs, do I need a current limiting resistor to protect the input, and if yes: in what range should it be? I thought maybe 47Ω?
3.
Am I correct when saying that µC inputs are high impedanced and almost no currents run into it, and therefore no resistor is needed?
4.
If in question 3 you state that no resistor is needed, what about the output current from the optocoupler that is stated at an average of 10mA??
best regards
HSE
I'm having a µC that is able to sink/source 3mA.
I have 2 inputs and 2 outputs that must be connected to some external devices through optocouplers that must be pretty fast.
First I thought of a 74OL6000 from fairchild, but they seems to be obsolete, or at least I can't find them anywhere. Then i looked through Fairchilds homepage for another one, that would be easier the get. The one i found was FOD0710 (12,5Mbit/s).
1.
Now I'm not sure if I need to connect any resistors on any side of optocouplers. I don't know, when controlling the output, and driving it low if the output should sink any current(for driving the optocoupler LED) or if the current runs from VCC to GND of the optocoupler, and no (mentionable) current runs through the output pin to GND.
2.
And for the inputs, do I need a current limiting resistor to protect the input, and if yes: in what range should it be? I thought maybe 47Ω?
3.
Am I correct when saying that µC inputs are high impedanced and almost no currents run into it, and therefore no resistor is needed?
4.
If in question 3 you state that no resistor is needed, what about the output current from the optocoupler that is stated at an average of 10mA??
best regards
HSE