1. ISO721DRG4 Substitution Conclusion The ISO721DRG4 can serve as a substitute for the SI8720BC-A-ISR, as both are single-channel, unidirectional, general-purpose digital isolators with compatible packages. However, critical differences must be carefully evaluated. Its isolation voltage is 2500 Vrms, lower than the original part's 3750 Vrms, making it unsuitable if the original design relies on higher isolation strength. On the other hand, its data rate of 100 Mbps—significantly higher than the original part's 15 Mbps—and superior dynamic performance (propagation delay ≤24 ns, pulse‑width distortion ≤2 ns) provide markedly improved high‑speed signal‑handling capability. However, its supply‑voltage range is narrower (3 V to 5.5 V versus the original part’s support down to 2.5 V), which may restrict low‑voltage applications. Additionally, its common‑mode transient immunity of 25 kV/µs (compared to 35 kV/µs for the original part) results in slightly weaker noise immunity in high‑noise environments; acceptability should be judged based on the actual electromagnetic conditions.