Texas Instruments LM3411M5-5.0/NOPB

Overview

LM3411M5-5.0/NOPB from Texas Instruments is a precision 5.0 V fixed-output shunt regulator with ±1% initial tolerance (standard grade), designed specifically to drive optocouplers in isolated DC-DC feedback loops. It features an open-emitter NPN output capable of 15 mA sink current, internal bandgap reference with curvature correction, and externally accessible compensation pin for loop stabilization. It operates across –40°C to +125°C and is used in flyback converters delivering 5 V at up to 1.5 A.

For engineers reviewing the LM3411M5-5.0/NOPB datasheet, LM3411M5-5.0/NOPB pinout, LM3411M5-5.0/NOPB application, or LM3411M5-5.0/NOPB equivalent, key selection considerations include its 5.0 V regulation accuracy over temperature, COMP pin accessibility for closed-loop stability tuning, SOT-23-5 package footprint, and role as secondary-side voltage reference in isolated power supplies.

Technical Context

The LM3411M5-5.0/NOPB integrates a trimmed bandgap reference, internally compensated op-amp, and NPN output transistor in a single die. Its regulation voltage is set by internal feedback resistors (70–118 kΩ) and stabilized via external capacitor between COMP and OUT pins.

It functions as a two-terminal shunt regulator where voltage at +IN relative to GND determines output conduction: below 5.0 V, OUT sinks negligible current; near or above 5.0 V, OUT sinks up to 15 mA to maintain regulation-enabling precise optocoupler LED drive without external resistors or trimming.

Key Specifications

Pinout & Package

LM3411M5-5.0/NOPB is housed in a 5-pin SOT-23 (DBV) package measuring 2.90 mm × 1.60 mm, optimized for space-constrained isolated power supply designs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TL431ACDR and LM4040C50IDBZR, LM3411M5-5.0/NOPB uniquely integrates a 5.0 V reference, NPN output driver, and COMP pin in one SOT-23-5 package-enabling compact, high-accuracy isolated feedback without external active components or trimming.

Availability

LM3411M5-5.0/NOPB is available at Aetrix Electronics and suitable for isolated flyback converters, precision buck regulators, LDO reference enhancement, and negative-voltage flyback systems requiring stable component supply and long-term production continuity.

Supply support for LM3411M5-5.0/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 and embedded processing technologies, with leadership in power management, signal chain, and high-reliability ICs.

The LM3411 product line was engineered for precision secondary-side regulation in isolated DC-DC converters-delivering fixed-voltage references with integrated optocoupler drive and loop compensation capability in ultra-small packages.

FAQ

What is the regulation voltage tolerance of LM3411M5-5.0/NOPB over temperature?

The LM3411M5-5.0/NOPB has a regulation voltage tolerance of ±1% over the full operating junction temperature range of –40°C to +125°C. At 25°C, the typical value is exactly 5.0 V, with min/max limits of 4.95 V and 5.05 V. This specification applies to the standard-grade version indicated by the part number suffix and is ensured via statistical quality control methods-not just room-temperature testing.

Can LM3411M5-5.0/NOPB drive an optocoupler directly without external components?

Yes, LM3411M5-5.0/NOPB can drive common optocouplers such as PC817 or TLP521 directly. Its open-emitter NPN output sinks up to 15 mA, sufficient for typical optocoupler LED forward currents. An external pull-up resistor (e.g., 1–10 kΩ) from OUT to bias voltage is required, but no series current-limiting resistor or transistor stage is needed-simplifying isolated feedback design.

What is the purpose of the NC pin on LM3411M5-5.0/NOPB?

The NC pin (Pin 3) on LM3411M5-5.0/NOPB has no internal electrical connection but is thermally tied to the die paddle. It must be soldered to the PCB copper pour to provide an effective thermal path. This improves power dissipation capability-especially critical when sinking 15 mA continuously-and helps maintain junction temperature within the 125°C limit under elevated ambient conditions.

How does the COMP pin function in LM3411M5-5.0/NOPB feedback loops?

The COMP pin on LM3411M5-5.0/NOPB is the inverting input of the internal error amplifier. Connecting an RC network (e.g., 100 pF–10 nF capacitor) between COMP and OUT sets dominant pole frequency and adjusts phase margin. This external compensation allows loop stabilization across diverse transformer leakage inductances and optocoupler CTR variations-critical for reliable transient response in isolated switching regulators.

Is LM3411M5-5.0/NOPB suitable for negative-input power supply topologies?

Yes, LM3411M5-5.0/NOPB supports negative-input flyback topologies. In configurations like Figure 26 of the datasheet, it serves as a level-shifted reference on the secondary side-regulating –5 V output while interfacing with buck-based controllers. Its ground-referenced +IN and GND pins allow flexible placement on either side of the transformer, enabling both positive and negative output generation without isolation compromise.