The LM385MX-1.2 is a fixed 1.235V shunt voltage reference from Texas Instruments, in an 8-SOIC surface-mount package. It is a two-terminal device that regulates voltage by shunting current to ground, requiring only a series resistor from the supply rail. Typical applications include low-drift bias supplies for op-amps, ADC references in instrumentation, and threshold-setting circuits in power supplies — any place a stable 1.235V rail is needed without a separate regulator.
The output tolerance is asymmetric: -2.43% to +2.02% at 25°C. That means a 1.235V nominal output can sit anywhere from about 1.205V to 1.260V. For a 12-bit ADC reference, that's roughly ±10 LSBs of initial error — acceptable for many industrial control loops but not for precision metrology without a trim. Wideband noise is specified at 60 µVrms over 10 Hz to 10 kHz. In a low-noise bias circuit, that's about 49 ppm of the output voltage — clean enough for a 10-bit system but marginal for a 16-bit SAR ADC without post-filtering. The temperature coefficient is 150 ppm/°C.
Obsolete — sourcing the LM385MX-1.2 today
The LM385MX-1.2 is officially classified as obsolete by Texas Instruments. Expect to work with a procurement specialist to locate a lot that matches your quantity and date-code requirements.
It reworks cleanly under hot air at 300°C to 350°C with a fine nozzle — the leads are visible and the thermal mass is low. No special bake-out is required for MSL Level 1 parts typical of this era.