1. LM431ACZ Substitution Conclusion The LM431ACZ can functionally replace the TL431ACZ in basic applications, but attention must be paid to potential impacts due to key performance degradation. The primary differences are as follows: accuracy decreases from ±1% to ±2%, which widens the initial error band when used as a voltage reference and may affect circuits sensitive to reference voltage precision; the minimum cathode operating current increases from 600µA to 1mA, requiring the supply circuit to provide a higher minimum bias current for stable operation—this could lead to startup failure or operating point drift in low‑power or light‑load designs. Additionally, the LM431ACZ is typically specified for commercial‑grade temperature ranges; if the original design targets industrial environments, its temperature suitability should be verified. In summary, substitution is acceptable in general voltage‑regulation or feedback circuits where precision is not critical and sufficient supply current is available, but re‑evaluation is necessary for precision or low‑power applications.