How can I calculate fan-out?
The fan-out can be calculated by dividing the output current IOH/IOL by the input current IIH/IIL of the IC in the subsequent stage. However, if the IC in the subsequent stage is a CMOS, there is little restriction in direct current due to fan-out because the input impedance of a CMOS is very high.
When the CMOS fan-out is calculated, increase in rising and trailing edge times due to the load capacity (input capacity if the IC in the subsequent stage and wire capacity) should be considered. It is required to check that the input rising edge and trailing edge meet the specification and that the device does not malfunction due to reflection of the transmission line.