1. TL431IZ Substitution Conclusion Substitution is conditionally feasible, but special attention must be paid to the degradation in precision and potential pinout compatibility issues. The TL431IZ (ST) shares fundamental functionality, output voltage range, and output current capability with the original TI TL431BCLPE3. Key differences are as follows: First, the tolerance has significantly degraded from ±0.5% to ±2.21%, expanding the initial reference voltage error range by approximately 4.4x. In applications where the original design demands tight voltage reference accuracy—such as high-precision power supplies or measurement circuits—direct substitution may cause system performance (e.g., output voltage accuracy, feedback loop stability) to fall short of the original specifications. Second, the minimum cathode operating current (I_Cathode(min)) has increased from 600µA to 1mA. Post-substitution, the minimum load current required for the reference to function properly is higher, which could cause startup issues or introduce unnecessary power consumption in designs with extremely light loads or those targeting ultra-low standby power. Third, while the package is described as TO-92, the suffix indicates "TO-92-2 (TO-226AC)", strongly suggesting its pinout may differ from the original's "TO-92-3 (TO-226AA)". If the PCB layout is not compatible, direct substitution will result in installation error. Substitution should only be considered in circuits where initial accuracy is not critical, operating current is sufficient, and pinout compatibility has been verified.