8-SOIC adjustable shunt reference — parametric scope
The Texas Instruments LM431AIM is a three-terminal adjustable shunt voltage reference in an 8-SOIC package — the same industry-standard footprint as the TL431 family, but specified with a ±2.2% initial tolerance and a 50ppm/°C typical temperature coefficient. Output is adjustable from a 2.495 V minimum up to 37 V, with a 100 mA cathode current capability that covers biasing optocouplers, setting error-amplifier references in off-line supplies, or clamping protection rails.
Tolerance and tempco — where the ±2.2% grade lands
The ±2.2% tolerance at 25°C is the middle-grade variant in the LM431 family — tighter than the standard ±2.5% bin, but not the precision ±1% or ±0.5% grades. The 1 mA minimum cathode current is the quiescent floor — below that the shunt loses regulation. At the 100 mA maximum, the 8-SOIC's thermal impedance becomes the limiting factor; the device dissipates about 370 mW at full output and 37 V drop, which stays within the package's SOA at 85°C ambient.
TL431 functional equivalence — what swaps and what doesn't
The TL431IDBVR shares the same basic shunt reference topology and the same ±2.2% tolerance grade, but comes in an SOT-23-5 package with a tape-and-reel format — the LM431AIM's 8-SOIC body is wider and has a different pinout (the TL431 uses pin 1 as cathode, while the LM431AIM follows the standard SOIC pin assignment). The parametric core — 2.495 V reference, 100 mA output, 50ppm/°C tempco — is identical, so a board spin or adapter footprint is needed for direct swap.