Texas Instruments LM4121IM5X-1.2

Overview

LM4121IM5X-1.2 from Texas Instruments (formerly National Semiconductor) is a precision micropower low-dropout voltage reference IC delivering a fixed 1.25 V output with ±0.5% initial accuracy, 50 ppm/°C temperature coefficient, and ±5 mA source/sink capability in SOT-23-5 package. It operates from 1.8 V to 12 V input, draws only 160 µA typical supply current, and features an enable pin for power-down mode (<2 µA). It is used in high-accuracy analog signal chains of portable instrumentation and battery-powered data acquisition systems.

For engineers reviewing the LM4121IM5X-1.2 datasheet, LM4121IM5X-1.2 pinout, LM4121IM5X-1.2 application, or LM4121IM5X-1.2 equivalent, key selection criteria include dropout voltage at 5 mA load, thermal hysteresis (0.5 mV/V), long-term stability (100 ppm over 1000 hrs), noise performance (20 µV_PP, 0.1–10 Hz), and guaranteed operation across −40°C to +85°C industrial temperature range.

Technical Context

The LM4121IM5X-1.2 employs a bandgap-based reference core with internal trimming for stable 1.25 V output. Its enable pin controls a high-impedance shutdown path that reduces quiescent current to <2 µA while maintaining fast wake-up response. The device uses a low-noise architecture optimized for ceramic output capacitors (0.022–0.047 µF) and exhibits minimal line regulation (0.009%/V) and load regulation (0.04%/mA over 1–5 mA).

It integrates a dedicated REF pin (Pin 1) for the fixed 1.25 V version-unconnected in normal operation-and a GND-referenced enable input (Pin 3) with logic-level thresholds (V_H = 1.5 V, V_L = 0.4 V). Output impedance remains below 1 Ω up to 10 kHz, supporting precision feedback loops in low-power regulators and ADC references.

Key Specifications

Pinout & Package

SOT-23-5 surface-mount package (2.92 mm × 1.6 mm × 1.1 mm), tape-and-reel packaging (3000 units/reel), top marking "R19B".

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar precision voltage reference applications.

Compared with LM4121IM5X-1.2, LM4040CIM3-ADJ/NOPB offers lower quiescent current but demands higher minimum voltage and lacks enable control, while REF3012AIDBZR provides superior accuracy and lower I_Q but omits the critical enable function and delivers 1.2 V instead of 1.25 V - making LM4121IM5X-1.2 uniquely suited for 1.25 V–referenced, battery-operated, enable-governed systems.

Availability

LM4121IM5X-1.2 is available at Aetrix Electronics and suitable for portable instrumentation, battery-powered test equipment, and industrial sensor transmitters requiring stable component supply, consistent parametric performance, and long-lifecycle availability.

Supply support for LM4121IM5X-1.2 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 (TI) is a global semiconductor leader specializing in analog and embedded processing technologies, with decades of heritage in precision analog ICs including voltage references, amplifiers, and data converters.

The LM4121 product line was designed specifically for micropower, low-voltage, enable-controlled precision reference applications in portable and industrial systems - emphasizing accuracy, stability, and minimal supply overhead.

FAQ

What is the output voltage tolerance and temperature coefficient of the LM4121IM5X-1.2?

The LM4121IM5X-1.2 provides a fixed 1.25 V output with ±0.5% initial accuracy at 25°C and a guaranteed temperature coefficient of 50 ppm/°C over −40°C to +125°C. This means its output drift is bounded to approximately ±0.625 mV across the full extended temperature range, supporting high-fidelity analog measurements in demanding environments.

Does the LM4121IM5X-1.2 require an external capacitor, and if so, what value and type?

Yes, the LM4121IM5X-1.2 requires a minimum 0.022 µF ceramic output capacitor for stability, with recommended values between 0.022 µF and 0.047 µF. Larger capacitors (up to 1 µF) may be used with tantalum types, but require additional 50 pF capacitor between OUT and REF pins. Ceramic capacitors with ESR of 0.1–0.5 Ω are optimal for transient response and noise suppression.

How does the enable pin of the LM4121IM5X-1.2 function, and what are its threshold voltages?

The enable pin (Pin 3) of the LM4121IM5X-1.2 is an analog input: applying ≥1.5 V (typical) enables the output, while ≤0.4 V (typical) places the device in power-down mode with supply current dropping below 2 µA. It draws only 7–15 µA when enabled and <0.1 µA when disabled, allowing direct interface with standard CMOS logic without level-shifting.

Can the LM4121IM5X-1.2 be used in a 1.8 V input system delivering 5 mA load current?

Yes - the LM4121IM5X-1.2 is explicitly characterized for operation down to 1.8 V input at 5 mA load, with typical dropout voltage of 0.55 V. This makes it suitable for direct regulation from single-cell LiFePO₄ (nominal 3.2 V) or two-series alkaline cells (fully discharged ~1.8 V), eliminating need for pre-regulation in compact portable designs.

What is the long-term stability and noise performance of the LM4121IM5X-1.2?

The LM4121IM5X-1.2 exhibits 100 ppm long-term stability after 1000 hours at 25°C and delivers 20 µV_PP (0.1–10 Hz) and 30 µV_RMS (10 Hz–10 kHz) output noise. These specifications support high-resolution data acquisition systems requiring repeatability over time and low-noise analog signal conditioning without post-processing filtering.