1. INA154U/2K5 Substitution Conclusion The INA154U/2K5 is not a viable direct substitute for the AD621BRZ. While both share the same package and have compatible supply voltage ceilings, their core difference lies in the amplifier architecture: the INA154 is a differential amplifier, whereas the AD621 is an instrumentation amplifier (INA). The INA154 lacks the inherent, easy-to-use high input impedance and configurable common-mode rejection ratio (CMRR) of an INA. Achieving similar performance would require an external precision resistor network, significantly increasing design complexity and introducing additional error sources. Furthermore, the INA154's input offset voltage (100 µV) is double that of the AD621 (50 µV), and its input bias current is unspecified (typically much higher than that of an INA). For applications involving high-precision, high-impedance signal sources (e.g., sensors), this will directly result in inferior DC accuracy and worse thermal drift performance. Its advantages include higher bandwidth, slew rate, and output drive current. However, its minimum operating voltage (8V) is higher than the AD621's (4.6V), which may prevent startup in single-supply or low-voltage systems. Substitution should only be considered in specific scenarios where dynamic performance and drive capability are critical, and where circuit redesign and a compromise on precision are acceptable.