Texas Instruments LM4121IM5-ADJ

Overview

LM4121IM5-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 160 µA typical supply current. It operates from 1.8 V to 12 V input and features enable control for power-down mode (<2 µA), making it suitable for battery-powered instrumentation and portable data acquisition systems.

For engineers reviewing the LM4121IM5-ADJ datasheet, LM4121IM5-ADJ pinout, LM4121IM5-ADJ application, or LM4121IM5-ADJ equivalent, key selection considerations include its adjustable output range (≥1.216 V), low dropout behavior, thermal hysteresis (0.5 mV/V), long-term stability (100 ppm over 1000 hrs), and SOT-23-5 package compatibility with space-constrained PCB layouts.

Technical Context

The LM4121IM5-ADJ implements a bandgap-based reference core with an external resistive divider connected to the ADJ pin (Pin 1) to set output voltage per V_OUT = V_REF(1 + R1/R2) − I_BIAS·R1, where V_REF = 1.216 V (min) and I_BIAS = 15–40 nA (out of ADJ pin). Its enable pin (Pin 3) provides analog-controlled shutdown with logic-low threshold ≤0.4 V.

It delivers stable operation with 0.022–0.047 µF ceramic output capacitors (ESR 0.1–0.5 Ω), supports load regulation of 0.01%/mA (1–5 mA), line regulation of 0.009%/V (1.8–12 V), and exhibits 20 µV_PP (0.1–10 Hz) and 30 µV_RMS (10 Hz–10 kHz) output noise - critical for high-resolution ADC biasing and precision regulator feedback.

Key Specifications

Pinout & Package

SOT-23-5 surface-mount package (2.92 mm × 1.6 mm × 1.1 mm), tape-and-reel delivery, JEDEC MO-178 compatible.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM4121IM5-ADJ, LM4040CIM3-ADJ requires external biasing and offers no enable control, while MAX6126AASA+ delivers far better accuracy and tempco but sacrifices power-down and ±5 mA drive - making LM4121IM5-ADJ optimal for battery-aware, moderate-accuracy, high-drive applications.

Availability

LM4121IM5-ADJ is available at Aetrix Electronics and suitable for portable instrumentation, precision data acquisition, and battery management systems requiring stable component supply with guaranteed long-term availability and consistent parametric performance.

Supply support for LM4121IM5-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 (TI) is a global semiconductor leader delivering analog and embedded processing solutions, with heritage in precision analog design dating to National Semiconductor's acquisition in 2011.

The LM4121 series was developed for micropower, low-voltage reference applications in portable and industrial systems - emphasizing low dropout, enable-controlled power management, and robustness across extended temperature ranges.

FAQ

What is the minimum input voltage required for LM4121IM5-ADJ to regulate at full load?

The LM4121IM5-ADJ requires a minimum input voltage of 1.8 V at 5 mA load to maintain regulation, with a typical dropout of 0.3 V. This allows reliable operation from partially discharged single-cell lithium or alkaline sources. The device remains functional down to 1.5 V input but may not sustain full-load accuracy or stability below 1.8 V as specified in the Electrical Characteristics table.

How does the ADJ pin bias current affect output voltage accuracy in LM4121IM5-ADJ?

The ADJ pin of LM4121IM5-ADJ sources 15–40 nA, which flows through the upper feedback resistor (R1) and introduces an error term of I_BIAS·R1. For example, with R1 = 100 kΩ, this adds up to 4 µV–400 µV offset. To minimize impact, use R1 ≤ 100 kΩ and account for this term in the output equation: V_OUT = V_REF(1 + R1/R2) − I_BIAS·R1 - a correction applied in precision designs.

Can LM4121IM5-ADJ be used with ceramic output capacitors smaller than 0.022 µF?

No - the LM4121IM5-ADJ is not guaranteed stable with output capacitors below 0.022 µF. The datasheet specifies 0.022 µF as the minimum ceramic capacitance (X7R or NP0) required for phase margin and transient response compliance. Using smaller values risks oscillation or excessive overshoot during load steps, especially above 1 mA. Always verify stability with scope-based load-step testing if deviating from recommended values.

What is the maximum output voltage achievable with LM4121IM5-ADJ?

The LM4121IM5-ADJ has no intrinsic upper limit on output voltage - it is determined solely by the external resistor divider ratio and input supply headroom. However, practical constraints apply: output must remain ≤ VIN − 0.3 V (dropout), and total power dissipation must stay within 350 mW (SOT-23 package limit). For example, at VIN = 12 V and I_LOAD = 5 mA, V_OUT must be ≤ 11.7 V to avoid exceeding thermal limits. Always calculate junction temperature under worst-case conditions.

Does LM4121IM5-ADJ support operation over the extended temperature range (−40°C to +125°C)?

Yes - LM4121IM5-ADJ guarantees 50 ppm/°C temperature coefficient and thermal hysteresis (0.5 mV/V) over −40°C to +125°C, and long-term stability (100 ppm) is characterized at 25°C. While initial accuracy (±0.5%) and certain parameters like line/load regulation are specified only over −40°C to +85°C, the device is qualified for extended-range use in automotive and industrial environments where reference drift is the dominant concern - consult TI's full extended-range characterization report for complete specs.