1. ISO721D Substitution Conclusion The ISO721D presents a downgrade risk in isolation withstand voltage and common-mode noise immunity, but it significantly outperforms the original part in speed and dynamic performance, making it a conditional substitute. The key differences are as follows: First, the isolation voltage of the ISO721D (2500 Vrms) is lower than that of the original part (3750 Vrms). In applications requiring higher insulation test voltages or stricter safety standards—such as industrial grid-side systems or medical equipment—direct substitution may fail to meet regulatory requirements. Second, its common-mode transient immunity (CMTI) of 25 kV/µs is lower than the original part’s 35 kV/µs. In high-noise environments generated by power switching circuits (e.g., motor drives, power supplies), the probability of data errors may increase. Third, its minimum operating voltage of 3 V is higher than the original part’s 2.5 V. If the existing circuit operates within the 2.5 V to 3 V range, the ISO721D will not function. However, with a data rate of 100 Mbps, shorter propagation delay, and lower pulse width distortion, it offers superior performance for high-speed digital signal transmission. Provided the above compromises are acceptable and the supply voltage is compatible, substitution is feasible.