Texas Instruments LM3402MR/NOPB

Overview

LM3402MR/NOPB from Texas Instruments is a monolithic 0.5-A constant-current buck regulator with integrated 0.7-Ω N-channel MOSFET, 200-mV current-sense reference, 6–42 V input range, and hysteretic controlled-on-time (COT) architecture for driving high-power LED strings in automotive lighting, industrial illumination, and general-purpose LED systems.

For engineers reviewing the LM3402MR/NOPB datasheet, LM3402MR/NOPB pinout, LM3402MR/NOPB application, or LM3402MR/NOPB equivalent, key selection considerations include its 300 ns minimum OFF-time, 735 mA peak current limit, thermal shutdown at 165°C, PWM dimming compatibility via TTL-level DIM pin, and support for ceramic-output-capacitor–free operation.

Technical Context

The LM3402MR/NOPB implements a controlled ON-time (COT) architecture combining hysteretic current-mode control with a voltage-dependent one-shot timer. Its CS pin compares sensed voltage across RSNS against a precise 200 mV reference to initiate switching, while RON sets t_ON inversely proportional to VIN - enabling stable regulation without loop compensation.

It integrates a 7-V internal LDO (VCC), bootstrap gate driver (BOOT–SW), and fast shutdown logic on the DIM pin. The device operates exclusively in continuous conduction mode (CCM), maintains constant frequency over input voltage variation in steady state, and features cycle-by-cycle current limiting with hiccup-mode recovery during sustained overcurrent.

Key Specifications

Pinout & Package

LM3402MR/NOPB is housed in an 8-pin VSSOP (DGK) package with exposed thermal pad (DAP), optimized for compact LED driver layouts and efficient PCB heat dissipation. Thermal pad must be connected to ground via ≥4 vias.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM3402MR/NOPB, LM3404MTX/NOPB trades simplified design for wider input range, while TPS92630QPWPRQ1 adds automotive safety features at the cost of higher BOM count and price - making LM3402MR/NOPB optimal for cost-driven, thermally constrained 12/24 V LED systems requiring zero-compensation design.

Availability

LM3402MR/NOPB is available at Aetrix Electronics and suitable for automotive lighting, industrial high-bay fixtures, and emergency exit signage requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for LM3402MR/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 leader specializing in analog, embedded processing, and power management ICs, with decades of expertise in LED driver innovation and automotive-grade reliability.

The LM3402MR/NOPB belongs to TI's high-efficiency LED driver product line, engineered specifically for cost-sensitive, thermally demanding constant-current applications in automotive, industrial, and architectural lighting.

FAQ

What is the maximum LED string voltage supported by LM3402MR/NOPB?

The LM3402MR/NOPB regulates output voltage based on input voltage and programmed ON-time. With its 300 ns minimum OFF-time, the maximum duty cycle limits VO(MAX) to approximately 0.97 × VIN. At VIN = 42 V, this yields ~40.7 V maximum output - sufficient for up to 12 white LEDs (VF ≈ 3.4 V) or 5 UV-C LEDs (VF ≈ 7.2 V). External Zener-based open-LED protection (e.g., 39 V Zener + 200 mV offset) is recommended for fail-safe clamping.

Can LM3402MR/NOPB operate without an output capacitor?

Yes, LM3402MR/NOPB supports capacitor-less operation because it regulates LED current-not voltage-and the inductor directly controls current ripple. The datasheet confirms stable operation with no CO, relying on Δi_F = Δi_L = (VIN − VO) × t_ON / L. A small 10-nF capacitor across the LED string is optional to dampen ringing at SW node during open-circuit events.

How does the DIM pin function during PWM dimming?

The DIM pin on LM3402MR/NOPB accepts TTL-level signals: logic low (< 0.8 V) disables the internal MOSFET and halts LED current flow, while logic high (> 2.2 V) enables regulation. Its 75 µA internal pullup ensures default-on behavior when left floating. Unlike enable pins on voltage regulators, DIM preserves VCC and bias circuitry during dimming - enabling sub-µs turn-on response critical for flicker-free dimming at 100–1000 Hz.

What thermal management is required for LM3402MR/NOPB at 500 mA?

At 500 mA output and 24 V input, LM3402MR/NOPB dissipates ~0.2 W (I² × R_DS(on) + switching losses). Its VSSOP package has R_θJA = 154.4°C/W - so with 25°C ambient, junction temperature reaches ~38.8°C above ambient (~64°C total), well below the 125°C max operating limit. Use the exposed DAP thermal pad with ≥4 thermal vias to inner ground plane to ensure reliable long-term operation at full load.

Is LM3402MR/NOPB compatible with ceramic output capacitors?

Yes, LM3402MR/NOPB explicitly supports all-ceramic output capacitors - a key advantage over older current-mode controllers requiring electrolytic or tantalum types for stability. Its hysteretic COT architecture eliminates phase-margin concerns, allowing use of low-ESR, high-frequency X5R/X7R ceramics (e.g., 10 µF, 50 V) to reduce size, improve reliability, and lower cost versus traditional capacitor solutions.