1. On-Resistance and Current Capability: The FDD8451 features a significantly lower Rds(on) (24 mΩ) compared to the AOD454A (30 mΩ), resulting in lower conduction loss and higher efficiency. However, the FDD8451’s continuous current rating is specified under different conditions (9A at Ta vs. 28A at Tc), while the AOD454A provides a straightforward 20A rating at Tc. This suggests that within a similar package and comparable power dissipation, the FDD8451 achieves lower Rds(on) through optimized wafer technology. Its rating methodology implies potentially lower current capability under harsh conditions relying solely on PCB heatsinking (Ta). 2. Switching Performance: The FDD8451’s total gate charge (Qg = 20 nC) is nearly double that of the AOD454A (10.8 nC), and its input capacitance (Ciss) is also larger. In switching applications, this leads to slower turn-on and turn-off times for the FDD8451, significantly increasing switching losses and imposing higher peak current demands on the gate driver circuit. 3. Thermal Characterization: The AOD454A provides more comprehensive thermal data (power dissipation ratings at both Ta and Tc), facilitating evaluation under different heatsinking scenarios. The FDD8451 only specifies power dissipation at Tc. While the numerical values are similar (30W vs. 37W), the absence of a Ta rating makes thermal assessment for natural convection designs less straightforward compared to the AOD454A. This reflects differences in the two companies’ datasheet conventions. 4. Technology Platform: The FDD8451 utilizes onsemi's PowerTrench® technology, typically optimized for low Rds(on) and compact size, potentially at the expense of some switching characteristics. The AOD454A does not specify a proprietary technology, and its parameters present a more balanced performance profile. This explains the inverse relationship between the two parts regarding Rds(on) and Qg. Summary: Replacement feasibility is highly application-dependent. For DC or low-frequency PWM applications (e.g., motor direct drive, load switches), the FDD8451's low conduction resistance offers a clear advantage. For high-frequency switching applications (e.g., DC-DC converters), the AOD454A's superior switching characteristics may yield higher overall system efficiency. Prior to final substitution, physical verification under the new drive and thermal conditions is essential.