Texas Instruments LM3406MH/NOPB

Overview

LM3406MH/NOPB from Texas Instruments is a monolithic 1.5-A constant-current buck LED driver with integrated 2.0-A N-channel MOSFET, true average current control via external sense resistor, and dedicated PWM dimming logic input. It operates from 6 V to 42 V input, delivers stable current to high-power LED arrays in automotive headlamps and industrial lighting systems, and features thermal shutdown and cycle-by-cycle current limiting.

For engineers reviewing the LM3406MH/NOPB datasheet, LM3406MH/NOPB pinout, LM3406MH/NOPB application, or LM3406MH/NOPB equivalent, key selection considerations include its 200-mV CS reference accuracy over temperature, programmable on-time via RON, TSSOP-14 exposed-pad package thermal performance (θJA = 50°C/W), and dual-dimming capability via DIM pin or VINS comparator.

Technical Context

The LM3406MH/NOPB implements a controlled-on-time (COT) architecture with inverse VIN/VO modulation to maintain relatively constant switching frequency in continuous conduction mode. Its transconductance error amplifier (Gm = 145 µS) regulates average CS voltage to 200 mV, enabling precise LED current set by RSNS = 0.2 V / IF.

Internal circuitry includes a 7-V linear regulator (VCC), bootstrap gate drive for the high-side MOSFET (RDS-ON = 0.37 Ω typ), and dual protection comparators: CS overvoltage (300 mV threshold) and thermal shutdown (165°C, 25°C hysteresis). The DIM pin supports TTL-compatible PWM dimming with 75-µA internal pull-up, while VINS enables two-wire input-voltage PWM dimming at 70% VIN threshold.

Key Specifications

Pinout & Package

TSSOP-14 package with exposed thermal pad (DAP), rated for 150°C max junction temperature and 50°C/W θJA with proper copper area and via count.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar constant-current buck LED driver applications.

Compared with LM3406HV/NOPB and TPS92630QPWPRQ1, the LM3406MH/NOPB offers optimal cost-performance balance for non-automotive 12/24 V systems requiring robust analog dimming, minimal external components, and proven field reliability without safety certification overhead.

Availability

LM3406MH/NOPB is available at Aetrix Electronics and suitable for automotive headlamps, industrial machine vision lighting, and outdoor street lighting requiring stable component supply, long-term manufacturability, and consistent parametric performance across production lots.

Supply support for LM3406MH/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 headquartered in Dallas, Texas, specializing in analog, embedded processing, and power management ICs with broad industrial, automotive, and consumer reach.

The LM3406 family belongs to TI's high-reliability LED driver product line, designed specifically for constant-current regulation of high-power LEDs in thermally demanding environments where precision, protection, and layout simplicity are critical.

FAQ

What is the maximum LED string voltage supported by the LM3406MH/NOPB?

The LM3406MH/NOPB does not regulate output voltage directly but adjusts it dynamically to maintain constant current. Its maximum output voltage (VO-MAX) is limited by minimum off-time (230 ns) and input voltage: VO-MAX ≈ VIN-MIN × (1 − fSW × 230 ns). At 12 V input and 500 kHz switching, VO-MAX ≈ 11.8 V. For higher LED string voltages, increase VIN or reduce fSW using larger RON. Always verify against the absolute maximum VOUT rating of −0.3 V to 45 V.

How do I calculate the current-sense resistor RSNS for a target LED current of 1.3 A using the LM3406MH/NOPB?

Use the formula RSNS = 0.2 V / IF, derived from the 200-mV CS reference voltage and true average current control architecture. For IF = 1.3 A, RSNS = 0.2 / 1.3 = 0.1538 Ω. Select a standard 1% tolerance metal-film resistor such as 0.154 Ω (154 mΩ), rated for ≥1 W to handle I²R power dissipation (1.3² × 0.154 ≈ 0.26 W). Place RSNS between CS and GND with Kelvin connections for accuracy.

Can the LM3406MH/NOPB operate without an output capacitor, and what are the trade-offs?

Yes, the LM3406MH/NOPB supports capacitor-less output operation due to its buck topology and controlled-on-time regulation, which inherently stabilizes inductor current. Removing the output capacitor reduces cost and board area but increases LED current ripple (ΔiF), potentially causing visible flicker or reduced efficacy. For human-viewable lighting, add a 10–47 µF ceramic capacitor to limit ripple to <±10% of IF. For machine vision, capacitor-less operation is acceptable if ΔiF remains within camera exposure window constraints.

What is the purpose of the RON pin on the LM3406MH/NOPB, and how does it affect switching frequency?

The RON pin programs the controlled on-time (tON) via an external resistor to VIN: tON ≈ 1×10⁻¹¹ × RON × VO. Since switching frequency fSW ≈ D / tON and duty cycle D depends on VIN and VO, RON indirectly sets nominal fSW. For example, with RON = 200 kΩ, VIN = 24 V, and VO = 12 V, tON ≈ 1.3 µs and fSW ≈ 500 kHz. Larger RON increases tON and lowers fSW, improving efficiency but increasing inductor size; smaller RON raises fSW, reducing passive size but increasing switching losses.

Does the LM3406MH/NOPB support analog dimming, or is it limited to PWM methods?

The LM3406MH/NOPB does not support analog (DC) dimming via variable reference or bias current. Its only dimming interfaces are digital: logic-level PWM on the DIM pin (0–100% duty cycle, TTL-compatible) and input-voltage PWM via the VINS comparator (two-wire method). Attempting analog control-such as injecting current into CS or varying VREF-violates the device's specified operation and degrades current accuracy, stability, and protection integrity. Use external PWM generation with clean edges and adequate drive strength for reliable dimming.