Texas Instruments LM3411M5X-3.3/NOPB

Overview

LM3411M5X-3.3/NOPB from Texas Instruments is a precision 3.3 V shunt regulator with ±1% initial tolerance, 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 COMP pin for loop compensation. Used in flyback converters delivering 3.3 V/250 mA with tight regulation.

For engineers reviewing the LM3411M5X-3.3/NOPB datasheet, LM3411M5X-3.3/NOPB pinout, LM3411M5X-3.3/NOPB application, or LM3411M5X-3.3/NOPB equivalent, key selection criteria include output voltage accuracy over –40°C to +125°C, quiescent current under 125 μA, transconductance up to 6 mA/mV, saturation voltage ≤1.2 V at 15 mA, and SOT-23-5 package compatibility with space-constrained power supply designs.

Technical Context

The LM3411M5X-3.3/NOPB implements a precision shunt regulation architecture using an internally compensated op-amp, trimmed bandgap reference, and NPN output transistor. Its +IN pin senses regulated voltage across external resistors or transformer secondary windings, while the COMP pin enables direct access to the error amplifier's inverting input for custom loop compensation.

It operates as a two-terminal shunt device in feedback paths where the OUT pin sinks current into an optocoupler LED to adjust PWM duty cycle on the primary side. The internal 39–65 kΩ feedback resistor network sets nominal 3.3 V regulation without external components, and temperature drift is minimized via curvature-corrected bandgap design ensuring ±1% tolerance over full industrial temperature range.

Key Specifications

Pinout & Package

LM3411M5X-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 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 LM4040C33IDBZR, the LM3411M5X-3.3/NOPB uniquely integrates a 3.3 V reference, error amplifier, and optocoupler-driver NPN transistor in one SOT-23-5 package-enabling complete isolated feedback functionality without external gain stages or resistor networks.

Availability

LM3411M5X-3.3/NOPB is available at Aetrix Electronics and suitable for isolated DC-DC converters, precision LDO references, and flyback regulator feedback systems requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.

Supply support for LM3411M5X-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 for isolated power supplies, targeting applications demanding tight voltage accuracy, minimal board area, and robust feedback loop stability in industrial, telecom, and medical power systems.

FAQ

What is the primary function of the LM3411M5X-3.3/NOPB in a power supply design?

The LM3411M5X-3.3/NOPB serves as a precision 3.3 V shunt regulator that drives optocouplers in isolated DC-DC feedback loops. It replaces discrete reference + transistor combinations by integrating a bandgap reference, error amplifier, and NPN output stage. In the LM3411M5X-3.3/NOPB, this enables accurate secondary-side voltage sensing and direct optocoupler LED control-critical for maintaining ±1% output regulation in flyback and forward converters without primary-side trimming.

How does the COMP pin on the LM3411M5X-3.3/NOPB affect system stability?

The COMP pin on the LM3411M5X-3.3/NOPB provides direct access to the inverting input of the internal error amplifier, allowing engineers to add external RC compensation networks. This adjusts loop gain and phase margin to counteract optocoupler CTR variation, transformer leakage inductance, and PCB parasitics. For the LM3411M5X-3.3/NOPB, typical designs use a capacitor from COMP to OUT (e.g., 10 nF) to achieve stable response in 50–100 kHz flyback systems-ensuring no overshoot or ringing during load transients.

Can the LM3411M5X-3.3/NOPB operate with input voltages below 3.3 V?

No-the LM3411M5X-3.3/NOPB requires the +IN pin voltage to reach at least the 3.3 V regulation threshold before the OUT pin begins sinking current. Below this, the device remains in high-impedance state with leakage current <0.5 μA. Operation is specified for input voltages ≥3.3 V (recommended) and absolute maximum 20 V. For sub-3.3 V sensing, the LM3411M5X-3.3/NOPB is unsuitable; alternative low-voltage references like TLV431 should be considered.

What is the maximum continuous output current rating for the LM3411M5X-3.3/NOPB?

The LM3411M5X-3.3/NOPB is rated for continuous output current up to 15 mA, as confirmed in its Recommended Operating Conditions table. This current flows from the external bias supply through the optocoupler LED into the OUT pin. Exceeding 15 mA risks thermal overstress due to limited power dissipation (300 mW max at 25°C ambient), especially given its SOT-23 package's R_θJA of 178.6°C/W. For higher-current optocouplers, the LM3411M5X-3.3/NOPB requires series limiting resistors or external buffer stages.

Does the LM3411M5X-3.3/NOPB require external resistors to set its 3.3 V output?

No-the LM3411M5X-3.3/NOPB includes factory-trimmed internal feedback resistors (39–65 kΩ) that establish the 3.3 V regulation point without any external components. This distinguishes it from adjustable shunt regulators like the TL431. The +IN pin connects directly to the regulated node, and the internal resistor divider ensures nominal 3.3 V reference accuracy. External resistors are only needed if modifying loop compensation via the COMP pin or adding filtering for noisy environments.