Texas Instruments LM431AIMX

Overview

LM431AIMX from Texas Instruments is an industrial-grade adjustable precision shunt regulator with 2.495 V reference voltage, ±17 mV reference voltage deviation over temperature, 0.75 Ω dynamic output impedance, and operation up to 36 V cathode voltage - used in feedback loops of linear and switching power supplies for stable voltage regulation.

For engineers reviewing the LM431AIMX datasheet, LM431AIMX pinout, LM431AIMX application, or LM431AIMX equivalent, this page delivers verified electrical specs, SOIC-8 package details, thermal derating guidance, and real-world implementation constraints for precision shunt regulation design.

Technical Context

The LM431AIMX operates as a 3-terminal programmable Zener replacement, using internal bandgap reference and error amplifier to maintain precise cathode-to-anode voltage via external resistor divider on the reference pin. Its closed-loop regulation requires 1–100 mA cathode current and functions across −40°C to +85°C.

It supports both shunt regulator and comparator modes: in regulation mode, it sinks variable current to hold output voltage; in open-loop mode, it compares reference pin voltage against internal 2.495 V threshold to drive external circuitry - with fast turnon response and low-output noise critical for feedback stability.

Key Specifications

Pinout & Package

LM431AIMX is packaged in an 8-pin SOIC (D package), 4.90 mm × 3.91 mm body size, with pins 2 and 8 assigned to Reference and Cathode respectively, and pins 3, 6, and 7 internally connected to Anode - enabling flexible PCB layout for high-side or low-side shunt configurations.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar adjustable shunt regulator applications.

Compared with TL431ACDR and LM431BIMX/NOPB, the LM431AIMX offers balanced trade-offs: wider temperature range than TL431ACDR and lower cost than LM431BIMX/NOPB while maintaining sufficient accuracy for most industrial feedback and monitoring tasks.

Availability

LM431AIMX is available at Aetrix Electronics and suitable for adjustable power supply feedback, voltage monitoring, current source/sink circuits, and Zener diode replacements requiring stable component supply across industrial temperature ranges.

Supply support for LM431AIMX includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and consumer markets.

The LM431 product line was designed specifically for precision voltage regulation and reference applications in space-constrained, thermally demanding systems - emphasizing stability, programmability, and package flexibility across SOIC, SOT-23, and TO-92 variants.

FAQ

What is the minimum cathode current required for LM431AIMX to maintain regulation?

The LM431AIMX requires a minimum cathode current of 0.4 mA to sustain regulation. Below this threshold, the device exits regulation mode and cathode voltage rises above the programmed value. This parameter is critical when sizing the external series resistor in shunt regulator designs - especially under worst-case conditions of low input voltage and high load current. The LM431AIMX datasheet specifies this value under "Electrical Characteristics" as IZ(MIN).

Can LM431AIMX replace a standard Zener diode directly in existing circuits?

Yes, LM431AIMX can replace many Zener diodes in feedback and reference applications, but requires two external resistors to set the output voltage - unlike a fixed Zener. For example, to replicate a 5.1 V Zener, connect R1 = 1.02 kΩ and R2 = 1 kΩ between cathode, reference, and anode. The LM431AIMX provides superior temperature stability (50 ppm/°C vs. ~5000 ppm/°C for Zeners) and lower dynamic impedance, but introduces additional layout considerations for the resistor divider.

What is the thermal derating behavior of LM431AIMX in SOIC-8 package?

The LM431AIMX in SOIC-8 package has a junction-to-ambient thermal resistance (RθJA) of 126.9 °C/W. At 25°C ambient, its maximum allowable power dissipation is 0.81 W. Above 25°C, it must be derated at 6.5 mW/°C - meaning at 70°C ambient, max power drops to 0.51 W. This derating directly limits usable cathode current at high output voltages; for instance, at 36 V cathode voltage, max continuous current reduces to ~14 mA above 70°C ambient.

How does the reference input current (IREF) of LM431AIMX affect resistor divider design?

The LM431AIMX reference input current is 2–4 μA at 25°C, rising to ≤1.2 μA over temperature. This small but non-zero current flows into the reference pin and creates a voltage error across the upper resistor (R1) in the feedback divider. To limit this error to <0.1%, R1 should be ≤10 kΩ. For higher-accuracy designs, use lower R1 values or compensate mathematically using VO = VREF × (1 + R1/R2) + IREF × R1 - a correction term explicitly defined in the LM431AIMX datasheet.

Is LM431AIMX suitable for use as a comparator, and what are the key constraints?

Yes, LM431AIMX can operate as a comparator in open-loop mode by applying an external voltage to the reference pin while holding cathode at a fixed potential. Its 2.495 V internal threshold and fast turnon response make it viable for overvoltage detection. However, it lacks rail-to-rail input capability - the reference pin voltage must stay within −0.5 V to VZ - and has no dedicated output stage, so cathode must drive external logic or optocoupler directly. Hysteresis must be added externally if noise immunity is required.