Texas Instruments LM431CIMX

Overview

LM431CIMX from Texas Instruments is a precision adjustable shunt regulator IC used as a programmable Zener replacement in voltage reference, current sink, and overvoltage protection circuits. It delivers 2.50 V nominal reference voltage (±10 mV tolerance), operates from 2.5 V to 36 V output range, supports 1–100 mA cathode current, and maintains 50 ppm/°C average temperature coefficient across –40°C to +85°C.

For engineers reviewing the LM431CIMX datasheet, LM431CIMX pinout, LM431CIMX application, or LM431CIMX equivalent, this page provides verified package mapping (SOIC-8), confirmed thermal performance (RθJA = 126.9°C/W), functional mode details (closed-loop shunt regulation and open-loop comparator use), and validated alternative parts for industrial power supply and voltage monitoring designs.

Technical Context

The LM431CIMX implements a bandgap-based precision reference with internal error amplifier and NPN pass transistor, enabling stable shunt regulation via external resistor divider feedback on the REF pin. Its operation requires only a series current-setting resistor between input and cathode, with no mandatory bypass capacitor-though a 0.1-µF ceramic cap is recommended for noise suppression.

It functions in two primary modes: closed-loop regulation (REF tied to output via R1/R2 divider) ensuring output stability as long as cathode current stays within 1–100 mA, and open-loop comparator mode (REF driven externally) for threshold detection applications such as overvoltage crowbar or delay timing circuits.

Key Specifications

Pinout & Package

LM431CIMX is housed in an 8-pin SOIC (D package) with 4.90 mm × 3.91 mm body size and RoHS-compliant green finish (CU SN). Pins 4 and 5 are internally unconnected (NC); all other pins serve defined regulator functions.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM431CIMX, TL431CDBVR offers higher precision but requires recalculating feedback resistors, while AS431ASTZ provides identical electrical specs in through-hole form but lacks RoHS compliance and has higher thermal resistance - both serve distinct design priorities rather than direct substitution.

Availability

LM431CIMX is available at Aetrix Electronics and suitable for industrial power supplies, battery management systems, and embedded voltage monitoring applications requiring stable component supply across extended temperature ranges and multi-year production cycles.

Supply support for LM431CIMX 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 specializing in analog and embedded processing technologies, with leadership in precision analog ICs and power management solutions.

The LM431 product line was designed for cost-effective, high-stability voltage reference and shunt regulation in industrial, computing, and communications equipment - emphasizing wide operating range, low quiescent current, and robust thermal performance.

FAQ

What is the reference voltage tolerance of the LM431CIMX?

The LM431CIMX has a reference voltage (VREF) of 2.50 V with a tolerance of ±10 mV at 25°C, corresponding to ±0.4% initial accuracy. This specification is guaranteed across the full operating temperature range of –40°C to +85°C, and is documented in Section 6.5 of the SNVS020H datasheet. The LM431CIMX belongs to the 'C' grade variant, which provides tighter tolerance than 'A' or 'B' grades.

Can the LM431CIMX be used as a comparator?

Yes, the LM431CIMX can operate in open-loop comparator mode by applying an external voltage to the REF pin instead of connecting it to a resistor divider. In this configuration, the device switches its cathode current based on whether the REF voltage exceeds 2.50 V. This functionality is explicitly described in Section 8.4 (Device Functional Modes) of the datasheet and used in applications like overvoltage protection and delay timers.

What is the maximum cathode voltage rating for the LM431CIMX?

The absolute maximum cathode voltage for the LM431CIMX is 37 V, as specified in Section 6.1 (Absolute Maximum Ratings) of the SNVS020H datasheet. Operation above this voltage risks permanent damage. For reliable regulation, the recommended operating condition limits cathode voltage to ≤36 V, aligning with the maximum programmable output range stated in the device description.

Does the LM431CIMX require an input bypass capacitor?

No, the LM431CIMX does not require an input bypass capacitor for basic regulation, but Texas Instruments recommends adding a 0.1-µF ceramic capacitor close to the cathode pin to reduce noise coupling and improve stability - especially in noisy switch-mode environments. This guidance appears in Section 10 (Power Supply Recommendations) and Section 11.1 (Layout Guidelines) of the datasheet.

How does the LM431CIMX differ from the LM431ACM/NOPB?

The LM431CIMX and LM431ACM/NOPB share the same SOIC-8 package and pinout, but differ in temperature grade and reference accuracy: LM431CIMX is rated for –40°C to +85°C (industrial grade) with 2.50 V ±10 mV VREF, while LM431ACM/NOPB is commercial-grade (0°C to +70°C) with 2.495 V ±5 mV VREF. Both are RoHS-compliant and functionally interchangeable only if the design accommodates the different temp range and tolerance.