Texas Instruments LM3402MMX

Overview

LM3402MMX from Texas Instruments is a monolithic 0.5-A constant-current buck regulator with integrated 0.7-Ω N-channel MOSFET, designed specifically for driving high-power LED arrays in automotive and industrial lighting. It operates from 6 V to 42 V input, delivers precise 200-mV current-sense threshold regulation, supports PWM dimming via TTL-compatible DIM pin, and features hysteretic controlled-on-time (COT) architecture eliminating loop compensation.

For engineers reviewing the LM3402MMX datasheet, LM3402MMX pinout, LM3402MMX application, or LM3402MMX equivalent, key selection considerations include its 8-pin VSSOP package with thermal pad, 735-mA peak current limit, 300-ns minimum off-time, internal 7-V VCC regulator, and open-LED protection capability using external Zener clamping.

Technical Context

The LM3402MMX implements a controlled-on-time (COT) buck topology combining hysteretic current sensing with a voltage-dependent one-shot timer. Its CS pin compares sensed voltage across RSNS against a 200-mV reference to trigger switch turn-on; ON-time is set by RON and VIN per t_ON = 1.34×10⁻¹⁰ × R_ON/V_IN, enabling stable operation without external compensation.

It integrates a high-side N-MOSFET (R_DS(on) = 0.7 Ω typ), bootstrap gate driver (10-nF CB required), internal 7-V linear regulator (VCC), and dual-protection comparators: 300-mV overvoltage/overcurrent shutdown at CS and thermal shutdown at 165°C with 25°C hysteresis.

Key Specifications

Pinout & Package

LM3402MMX is housed in an 8-pin VSSOP (DGK) package with exposed thermal pad (DAP), measuring 3.00 mm × 3.00 mm. The DAP must be soldered to PCB ground plane using 4–6 thermal vias for effective heat dissipation (R_θJA = 154.4°C/W).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM3402HVMMX and MPQ4425AGU-AEC1-P, the LM3402MMX provides the most cost-effective solution for 12/24 V LED lighting where extended input range or automotive qualification are unnecessary - retaining full feature parity including PWM dimming, open-LED protection, and ceramic-capacitor support.

Availability

LM3402MMX is available at Aetrix Electronics and suitable for automotive headlamps, industrial high-bay fixtures, commercial signage backlights, and emergency exit lighting requiring stable component supply across production lifecycles.

Supply support for LM3402MMX 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 ICs and LED driver innovation since 2006.

The LM3402 product line was engineered as a family of monolithic constant-current buck regulators targeting high-reliability LED lighting in automotive and industrial environments - emphasizing integration, thermal robustness, and ease of design.

FAQ

What is the maximum LED string voltage supported by the LM3402MMX?

The LM3402MMX does not regulate output voltage directly but limits it via duty cycle constraints. With 300 ns minimum off-time and programmable ON-time, VO(MAX) = VIN × t_ON/(t_ON + 300 ns). At VIN = 42 V and t_ON = 810 ns (max for LM3402), VO(MAX) ≈ 31 V. For a 3.4-V LED, this supports up to nine in series. The LM3402MMX datasheet confirms this calculation in Section 7.3.3.

Does the LM3402MMX require an external bootstrap capacitor?

Yes, the LM3402MMX requires a 10-nF ceramic capacitor between BOOT and SW pins to sustain gate drive for its integrated high-side N-MOSFET. This capacitor charges through the internal bootstrap diode when the switch is off and floats to provide gate-source voltage during conduction. Omitting it causes immediate gate drive failure and device shutdown.

Can the LM3402MMX operate without an output capacitor?

Yes, the LM3402MMX supports capacitor-less operation due to its current-regulating architecture. The inductor and LED form a direct current path; ripple current is controlled by t_ON, L, and VIN. TI's datasheet (Section 8.1.3) explicitly validates this mode and recommends ≥25 mV ripple at CS for SNR - achievable with appropriate RSNS and L selection.

How does the LM3402MMX handle open-circuit LED failure?

The LM3402MMX detects open-circuit conditions via its CS pin overvoltage comparator (300 mV threshold). When an LED string opens, VSNS drops to zero, forcing maximum duty cycle until VO approaches VO(MAX); the comparator then disables the switch, preventing destructive overvoltage. External Zener clamping (Figure 18) adds secondary protection.

What is the thermal performance of the LM3402MMX in its VSSOP package?

In the 8-pin VSSOP (DGK) package, the LM3402MMX has R_θJA = 154.4°C/W (JEDEC JESD51-7 standard) and R_θJC(bot) = 3.2°C/W. With proper DAP grounding via 4–6 vias to inner ground plane, it sustains 500 mA continuous output at 125°C junction temperature. Thermal shutdown activates at 165°C with 25°C hysteresis to ensure safe recovery.