1. BLM18AG121SN1D Substitution Conclusion The BLM18AG121SN1D is fully compatible with the original part, HPZ1608U101-R80TF, in key mechanical and electrical characteristics such as package size and rated current, making it a viable direct substitute. However, two technical differences require consideration for their potential impact: First, the impedance difference: the BLM18AG121SN1D exhibits an impedance of 120 Ω at 100 MHz, which is 20 Ω higher than the original part's 100 Ω. This results in slightly stronger suppression of high-frequency noise at the same frequency, potentially causing minor shifts in the filter's bandwidth or attenuation profile. It is necessary to verify whether this meets the noise suppression requirements for the target frequency band. Second, the DC resistance (DCR) difference: the maximum DCR of the BLM18AG121SN1D is 180 mΩ, slightly lower than the original part's 200 mΩ. This contributes to reduced power loss and voltage drop across the current path, offering a marginal positive effect on power supply efficiency. In summary, if the circuit has a relaxed tolerance for impedance value (e.g., allowing ±20% deviation) and no specific frequency response requirements, this part can be safely substituted. Nevertheless, it is advisable to conduct in-circuit noise testing to ensure performance matching.