Texas Instruments LM4128AMFX-3.3

Overview

LM4128AMFX-3.3 from National Semiconductor is a precision micropower series voltage reference in SOT-23-5 package, delivering 3.3 V output with ±0.1% initial accuracy, 75 ppm/°C temperature coefficient, and 60 µA quiescent current. It features an enable pin for 3 µA shutdown mode, supports up to 20 mA load, and operates across −40°C to +125°C - ideal for battery-powered instrumentation and portable data acquisition systems.

For engineers reviewing the LM4128AMFX-3.3 datasheet, LM4128AMFX-3.3 pinout, LM4128AMFX-3.3 application, or LM4128AMFX-3.3 equivalent, key selection considerations include dropout voltage (≤400 mV at 10 mA), stability with capacitive loads up to 10 µF, line regulation (85 ppm/V), load regulation (25–120 ppm/mA), and thermal hysteresis (75 ppm) over full temperature range.

Technical Context

The LM4128AMFX-3.3 uses a band-gap-derived reference core optimized for low-power, high-accuracy operation in space-constrained designs. Its series architecture eliminates need for external stabilization capacitors while maintaining stability with ceramic output capacitance up to 10 µF.

It integrates an enable input (EN) referenced to VIN, with defined VIH/VIL thresholds (65%/35% of VIN), enabling precise power sequencing. Dropout voltage remains ≤400 mV at 10 mA load, supporting operation from as low as 3.7 V input across the full temperature range.

Key Specifications

Pinout & Package

SOT-23-5 package (NS package number MF05A), 1.6 mm × 2.9 mm footprint, surface-mount, lead-free compatible.

Key Features

Applications

Equivalent & Alternatives

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

Compared with REF3033AIDBZR and MAX6029AEUR+T, the LM4128AMFX-3.3 offers superior load regulation (25 ppm/mA vs ≥50 ppm/mA), lower dropout (400 mV vs 600 mV), and guaranteed stability with 10 µF capacitive loads - making it optimal for high-precision, low-voltage, and dynamically loaded systems.

Availability

LM4128AMFX-3.3 is available at Aetrix Electronics and suitable for portable instrumentation, battery-powered test equipment, and industrial analog input modules requiring stable component supply with consistent parametric performance across production lots.

Supply support for LM4128AMFX-3.3 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

National Semiconductor was a U.S.-based analog semiconductor company acquired by Texas Instruments in 2011; its precision reference portfolio remains widely deployed in industrial and automotive systems.

The LM4128 series was designed specifically for micropower, high-accuracy voltage referencing in space-constrained, battery-operated, and thermally demanding applications - emphasizing low dropout, capacitor-free stability, and AEC-Q100 qualification paths.

FAQ

What is the minimum input voltage required for stable operation of the LM4128AMFX-3.3?

The LM4128AMFX-3.3 requires VIN ≥ VREF + 400 mV, i.e., ≥3.7 V at 10 mA load. At lighter loads, dropout decreases - e.g., 200 mV typical at 10 mA for 3.3 V version - but 3.7 V ensures guaranteed regulation across temperature and process variation. Operation below this threshold risks output collapse or increased noise.

Does the LM4128AMFX-3.3 require an input capacitor, and if so, what value is recommended?

Yes - a minimum 0.1 µF ceramic (X5R/X7R) input capacitor (CIN) is mandatory for stable operation per datasheet. When using an output capacitor (COUT), CIN must be ≥ COUT; for no COUT, CIN ≥ 0.1 µF. For improved noise suppression and startup behavior, 4.7–22 µF is recommended, placed close to the VIN and GND pins of the LM4128AMFX-3.3.

Can the LM4128AMFX-3.3 drive a 10 µF capacitive load without oscillation?

Yes - the LM4128AMFX-3.3 is explicitly characterized and guaranteed stable with capacitive loads up to 10 µF, including low-ESR ceramic types. This eliminates need for series isolation resistors or ferrite beads often required with other references, simplifying design and improving transient response in ADC reference buffer applications.

What is the purpose of Pin 1 (N/C) on the LM4128AMFX-3.3, and how should it be handled on the PCB?

Pin 1 is a no-connect terminal - not internally bonded and electrically isolated. It must be left floating with no trace, pad, or solder mask opening. Connecting Pin 1 to any net (including GND or VIN) violates the datasheet and may cause unpredictable behavior or parametric shift due to parasitic coupling in the SOT-23-5 die layout.

How does the enable pin (Pin 3) of the LM4128AMFX-3.3 interface with standard logic families?

The LM4128AMFX-3.3 EN pin is VIN-referenced: VIH ≥ 65% VIN and VIL ≤ 35% VIN. When VIN = 5 V, this translates to VIH ≥ 3.25 V and VIL ≤ 1.75 V - compatible with 3.3 V and 5 V CMOS outputs. For 1.8 V logic, use a level-shifter or pull EN to VIN via resistor; never leave EN floating, as internal pull-up (~2 µA) is insufficient for noise immunity.