Texas Instruments LM4121IM5X-ADJ

Overview

LM4121IM5X-ADJ from Texas Instruments (formerly National Semiconductor) is a precision micropower adjustable voltage reference IC with 0.5% initial accuracy, 50 ppm/°C temperature coefficient, ±5 mA source/sink capability, and enable-controlled power-down mode consuming <2 µA. It operates from 1.8 V to 12 V input and targets low-power analog signal chains in portable instrumentation and battery-powered systems.

For engineers reviewing the LM4121IM5X-ADJ datasheet, LM4121IM5X-ADJ pinout, LM4121IM5X-ADJ application, or LM4121IM5X-ADJ equivalent, key selection criteria include its adjustable output architecture, low dropout behavior down to 1.5 V, thermal hysteresis of 0.5 mV/V, long-term stability of 100 ppm over 1000 hours, and SOT-23-5 package compatibility with space-constrained PCB layouts.

Technical Context

The LM4121IM5X-ADJ implements a bandgap-based reference core with an external resistive divider connected to the ADJ pin (Pin 1), enabling programmable output voltages above 1.216 V. Its internal enable circuitry provides clean turn-on/off control with logic-compatible thresholds (V_H = 1.5 V, V_L = 0.2 V) and <6 µA enable current.

It achieves low-noise performance (20 µV_PP at 0.1–10 Hz) and stable operation with 0.022–0.047 µF ceramic output capacitors. Load regulation is specified at 0.01%/mA for 1–5 mA loads, and line regulation is 0.009%/V across 1.8–12 V input range - critical for variable-supply applications like Li-ion battery monitoring.

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 per reel), top marking "R20B" indicating adjustable output and ±0.5% tolerance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6126AASA+T and ADR3425ARJZ-R7, the LM4121IM5X-ADJ trades tighter initial accuracy and lower tempco for on-the-fly output adjustability, sub-2 µA shutdown, and SOT-23-5 compatibility - making it optimal for cost-sensitive, battery-constrained systems needing flexible reference voltage scaling.

Availability

LM4121IM5X-ADJ is available at Aetrix Electronics and suitable for portable instrumentation, battery-powered data acquisition, and industrial sensor signal conditioning requiring stable component supply and long-lifecycle support.

Supply support for LM4121IM5X-ADJ 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 delivering analog and embedded processing solutions, with heritage in precision analog design dating to National Semiconductor's legacy.

The LM4121 product line was engineered for micropower, low-dropout voltage references in space- and energy-constrained systems - emphasizing accuracy, thermal stability, and ease of integration in portable and industrial equipment.

FAQ

What output voltage range can be achieved with LM4121IM5X-ADJ?

The LM4121IM5X-ADJ supports adjustable output voltages starting from 1.216 V upward, determined by the external resistor divider connected to the ADJ pin. Using the formula V_OUT = V_REF(1 + R1/R2) − I_BIAS·R1 (where V_REF = 1.216 V and I_BIAS = 15–40 nA), outputs up to 10 V are feasible with appropriate resistor selection and input headroom. The LM4121IM5X-ADJ does not regulate below 1.216 V.

How does the enable pin function on LM4121IM5X-ADJ?

The EN pin (Pin 3) is an analog input that controls output activation: applying ≥1.5 V enables the reference output, while ≤0.2 V forces shutdown with <2 µA supply current. No external pull-up is required; CMOS/TTL logic outputs interface directly. The LM4121IM5X-ADJ exhibits minimal enable hysteresis, so clean digital edges are recommended to avoid output glitches.

What capacitor values are recommended for LM4121IM5X-ADJ stability?

The LM4121IM5X-ADJ is optimized for 0.022 µF to 0.047 µF ceramic output capacitors with ESR ≤ 0.5 Ω. Smaller values risk instability; larger ceramics may cause oscillation. For improved transient response beyond 0.047 µF, use 1 µF tantalum with a 50 pF capacitor between OUT and ADJ pins. Input capacitance is optional but a 0.1 µF ceramic helps suppress line transients.

Can LM4121IM5X-ADJ operate from a single-cell Li-ion battery?

Yes - the LM4121IM5X-ADJ functions down to 1.5 V input at 5 mA load, well within the 2.5–4.2 V discharge curve of a single Li-ion cell. Its 160 µA quiescent current and <2 µA shutdown current make it ideal for battery-powered applications where runtime and low-power sleep modes are critical. The LM4121IM5X-ADJ maintains 0.5% accuracy across this input range.

What is the maximum load current LM4121IM5X-ADJ can source or sink?

The LM4121IM5X-ADJ delivers ±5 mA continuous output current - meaning it can source up to +5 mA into a load or sink up to −5 mA from a load. This capability supports driving moderate-impedance op-amp inputs, DAC reference inputs, or small LED indicators. Exceeding ±5 mA risks output voltage deviation beyond spec and potential thermal stress; the LM4121IM5X-ADJ short-circuit current is rated at 15–30 mA depending on input voltage.