1. PS8501L2-AX Substitution Conclusion Based on core electrical parameters and package, the PS8501L2-AX is a viable direct substitute for the HCPL-4562320. However, two key differences must be noted and their impact on the application assessed. The differences are as follows: First, the forward voltage (Vf) of the PS8501L2-AX is 1.7V (Typ.), which is higher than the original part's 1.3V (Typ.). Under the same input-side current-limiting circuit conditions, this will reduce the current through the LED. This reduction may lead to decreased output-side current drive capability. It is therefore necessary to verify that the original design's drive current still meets the CTR requirement of the PS8501L2-AX (Min. 15% @ 16mA) to ensure switching reliability. Second, the maximum output withstand voltage of the PS8501L2-AX is 35V, significantly higher than the original part's 20V. This is a positive advantage, allowing the output to withstand higher voltage stress and improving system safety. Additionally, the PS8501L2-AX specifies switching time parameters (220ns/350ns), which were not provided for the original part. If the original design is sensitive to switching speed, these parameters can serve as a basis for verification. In summary, provided that the input drive current is sufficient and the package pinout is compatible, the PS8501L2-AX can be considered a valid substitute.