I have seen some web pages defining that current sinking and current sourcing are same. But the truth is that they are different. This is a tutorial about current sinking and current sourcing in Integrated Circuits(IC).
When we skim through the data sheet of certain micro controllers or other IC's, we do come with a term known as current sinking and current sourcing. These current sinking and current sourcing rating are the current that the IC pin can handle. Current sinking and sourcing rates are important while designing circuits. These ratings determine the current capacity to drive external devices. Lets start with a simple definition and then an example.
It is the amount of current that can flow in to the IC pin.
It is the amount of current that can flow out from the IC pin.
Before going through the example case, lets understand about current. Current is the amount of charge flowing. Current flows from a higher potential to a lower potential.
The current sourcing and sinking can be easily understood from the figure below.
Most of the TTL can sink up to 16mA and source 250uA. Just think that micro-controller port pin can sink 20mA and source 60uA. Then the LED 3 will glow and LED 4 will not glow. The reason is that, for an LED to glow, sufficient amount of current is required. The LED 3 is connected in such a way that current will flow into(current sinking) the IC. Since the micro-controller port pin can sink 20mA, LED will glow. The LED 4 is connected in such a way that current will flow out(current sourcing) the IC. Since the micro-controller port pin can source 60uA, LED will not glow because of less amount of current to drive LED.