1. Thermal Performance and Current Rating Basis: This is the fundamental difference. The STD80N3LL’s nominal ratings of 80A/75W are specified at case temperature (Tc). Its high-power capability can only be realized with an effective heatsink that efficiently transfers heat to the case. In contrast, the NTD4965NT4G specifies 13A/1.39W at ambient temperature (Ta), while its 68A rating is based on Tc. This highlights the extreme sensitivity of its performance to thermal management. Under identical PCB and natural convection conditions, the NTD4965NT4G’s safely achievable continuous current will be significantly lower than that of the STD80N3LL, as its design relies more heavily on PCB copper pour for heat dissipation. 2. On-Resistance (Rds(on)) Test Conditions: The NTD4965NT4G’s 4.7mΩ is measured at 30A, whereas the STD80N3LL’s 5.2mΩ is measured at 40A. This implies that the actual conduction losses of both devices are comparable at the same current level, though the STD80N3LL may exhibit better linearity in its on-resistance at higher currents. However, due to difference #1 (thermal performance), the NTD4965NT4G may never operate at such high currents in practice, preventing it from leveraging its lower Rds(on). 3. Input Capacitance (Ciss) Test Voltage: While the values are similar, they are measured at different drain-source voltages (25V vs. 15V). MOSFET capacitance characteristics vary with Vds. This reflects a subtle difference in manufacturer characterization practices. The practical impact is that driver design should include some margin, though both devices are expected to deliver similar switching speeds. Summary: While the static parameters of the two devices are comparable, dynamic thermal performance is the key factor determining substitutability. If the original design uses the STD80N3LL with adequate cooling (e.g., a heatsink), replacing it with the NTD4965NT4G requires verification that the junction temperature remains within limits under worst-case conditions. If the original design relies on PCB natural convection cooling, the substitution carries a high risk of failure.