1. AP2181SG-13 Substitution Conclusion Based on a detailed comparison, the AP2181SG-13 cannot serve as a direct drop-in replacement for the TPS2021DG4. It may only be considered for functional substitution under specific, redesigned conditions. The key differences and their implications are as follows: First, the output stage polarity differs fundamentally. The TPS2021DG4 employs an N-channel switch, requiring a charge pump or boost circuit for high-side drive. In contrast, the AP2181SG-13 uses a P-channel switch, which can be driven with simple gate-level translation. These drive architectures are entirely incompatible; a direct swap would result in circuit failure. Second, the switch types and performance priorities are distinct. The AP2181SG-13 is marketed as a USB switch featuring reverse current protection, making it more suitable for applications like USB ports where backflow prevention is critical. However, its on-resistance (95mΩ) is significantly higher than that of the TPS2021DG4 (33mΩ). This leads to greater power dissipation and higher temperature rise under identical load currents, which is detrimental for high-efficiency or space-constrained designs. Finally, while the rated current capability differs (AP2181SG-13 supports 1.5A vs. 600mA), the practical sustainable current may not see a substantial increase due to limitations imposed by the package thermal resistance and the disadvantage in Rds_on. In summary, substitution could be validated if the system can accommodate a redesigned drive circuit, accept higher conduction losses, and requires enhanced reverse current protection. Otherwise, a direct replacement is not recommended.