Texas Instruments LM3411AM5-3.3/NOPB

Overview

LM3411AM5-3.3/NOPB from Texas Instruments is a precision 3.3 V shunt regulator with ±0.5% initial tolerance (A-grade), designed specifically to drive optocouplers in isolated DC-DC feedback loops. It features an internal compensated op-amp, bandgap reference, open-emitter NPN output transistor, and trimmed internal feedback resistors - delivering 3.3 V regulation at up to 15 mA load current with 50 µV_RMS output noise and 1.2 V saturation voltage.

For engineers reviewing the LM3411AM5-3.3/NOPB datasheet, LM3411AM5-3.3/NOPB pinout, LM3411AM5-3.3/NOPB application, or LM3411AM5-3.3/NOPB equivalent, key selection criteria include its fixed 3.3 V output, SOT-23-5 package compatibility, COMP pin for loop compensation, GND-referenced +IN sensing, and suitability for high-precision secondary-side regulation in flyback, buck, and LDO-based power supplies.

Technical Context

The LM3411AM5-3.3/NOPB implements a precision shunt regulation architecture where the +IN pin senses output voltage relative to GND, and the OUT pin sources current into an optocoupler LED to close the isolation barrier feedback loop. Its internally compensated error amplifier includes an externally accessible COMP pin for frequency compensation, enabling stable closed-loop control across varying transformer leakage and optocoupler CTR.

This device operates as a two-terminal shunt element in series with the optocoupler LED, using a trimmed 39–65 kΩ internal feedback resistor divider to set the 3.3 V reference point. The open-emitter NPN output delivers up to 15 mA while maintaining low quiescent current (110 µA typ. at 25°C) and tight temperature drift (±1% over –40°C to +125°C).

Key Specifications

Pinout & Package

LM3411AM5-3.3/NOPB is housed in a 5-pin SOT-23 (DBV) surface-mount package measuring 2.90 mm × 1.60 mm, optimized for space-constrained secondary-side PCB real estate in isolated power supplies.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TL431ACDBVR and LM4040C33IDCKR, the LM3411AM5-3.3/NOPB uniquely integrates a precision 3.3 V reference, compensated error amplifier, and 15 mA optocoupler driver in one SOT-23-5 package - eliminating external resistors, transistors, and compensation components required by alternatives.

Availability

LM3411AM5-3.3/NOPB is available at Aetrix Electronics and suitable for isolated flyback converters, precision buck regulators, high-accuracy LDO systems, and negative-output DC-DC designs requiring stable component supply with guaranteed long-term manufacturability.

Supply support for LM3411AM5-3.3/NOPB 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, embedded processing, and power management ICs, with leadership in high-reliability power conversion solutions.

The LM3411 product line delivers precision secondary-side regulation ICs optimized for optocoupler-driven isolated switching supplies - targeting design goals of ±0.5% output tolerance, minimal external components, and robust loop stability across temperature and load.

FAQ

What is the primary function of the LM3411AM5-3.3/NOPB in a power supply design?

The LM3411AM5-3.3/NOPB serves as a precision 3.3 V shunt regulator and optocoupler driver in the secondary-side feedback path of isolated DC-DC converters. It replaces discrete reference + transistor combinations by integrating a bandgap reference, compensated op-amp, and open-emitter NPN output - enabling accurate, stable regulation without external resistors or trimming. Its COMP pin allows direct loop compensation tuning for optocoupler-based systems.

Does the LM3411AM5-3.3/NOPB require external resistors to set its output voltage?

No, the LM3411AM5-3.3/NOPB does not require external resistors to set its 3.3 V output. It contains trimmed internal feedback resistors (39–65 kΩ) that establish the regulation voltage directly at the +IN pin relative to GND. This eliminates the need for precision external dividers, potentiometers, or calibration - supporting ±0.5% initial tolerance and ±1% over temperature without user adjustment.

How is the COMP pin used in LM3411AM5-3.3/NOPB applications?

The COMP pin on the LM3411AM5-3.3/NOPB is the inverting input of the internal error amplifier and is used for closed-loop frequency compensation. In typical designs, a capacitor (e.g., 10 nF) is connected from COMP to OUT to stabilize the feedback loop when driving optocouplers. This external network adjusts phase margin and transient response - critical for maintaining stability across variations in optocoupler CTR, transformer leakage, and load dynamics.

Can the LM3411AM5-3.3/NOPB drive standard optocouplers directly?

Yes, the LM3411AM5-3.3/NOPB can drive standard optocouplers directly via its open-emitter NPN output (Pin 5). With a maximum sink current of 15 mA and 1.2 V saturation voltage, it interfaces cleanly with common optocoupler LEDs (e.g., PC817, SFH615A) when paired with an appropriate current-limiting resistor on the collector side. Its low output noise (50 µV_RMS) further ensures reliable operation in noise-sensitive feedback paths.

What thermal considerations apply to the LM3411AM5-3.3/NOPB in continuous 15 mA operation?

In continuous 15 mA operation, the LM3411AM5-3.3/NOPB dissipates up to ~18 mW (1.2 V × 15 mA) at the output stage. With R_θJA = 178.6°C/W in the SOT-23 package, ambient temperature must be limited to ≤75°C to keep junction temperature below 125°C. For sustained high-current use, solder Pin 3 (NC) to copper pour for enhanced thermal conduction - improving power handling by reducing effective R_θJA.