1. AP2181SG-13 Substitution Conclusion Overall, the AP2181SG-13 can directly replace the TPS2021DRG4 in terms of functionality and package footprint. However, two key technical differences must be considered: First, the output stage changes from N-channel to P-channel. While the driving logic remains inverting, the internal power transistor structure differs, which may affect transient response and driving efficiency. Second, the on-resistance increases from 33mΩ to 95mΩ. This will result in higher conduction loss and temperature rise under the same load current. Although the AP2181SG-13 has a higher rated maximum current (1.5A), its practical current capability may be limited by thermal conditions. Additionally, the AP2181SG-13 introduces reverse current protection, making it suitable for applications such as USB ports where backflow prevention is required. The original device is more oriented toward general-purpose switching designs. If the system does not demand very low conduction voltage drop, can accommodate P-channel characteristics, and benefits from enhanced current protection, the substitution is feasible. Conversely, if ultra-low conduction loss is critical or the original circuit is optimized for an N-channel FET, thermal design and performance matching should be re-evaluated before replacement.