Texas Instruments LM3402MM

Overview

LM3402MM from Texas Instruments is a monolithic 0.5-A constant-current buck regulator with integrated 0.7-Ω N-channel MOSFET, 6–42 V input range, 200 mV current-sense threshold, and hysteretic controlled-on-time (COT) architecture-designed specifically to drive high-power LED strings in automotive headlamps and industrial lighting systems.

For engineers reviewing the LM3402MM datasheet, LM3402MM pinout, LM3402MM application, or LM3402MM equivalent, key selection considerations include its VIN-dependent programmable ON-time, 300 ns minimum OFF-time limiting VO(MAX), internal 7-V VCC regulator, thermal shutdown at 165°C, and PWM dimming compatibility via TTL-level DIM pin.

Technical Context

The LM3402MM implements a controlled-on-time (COT) architecture combining hysteretic current regulation with a one-shot ON-timer inversely scaled by VIN and RON. Its CS pin compares sensed voltage across RSNS against a precise 200 mV reference to initiate switching, while the ON-time (e.g., 2.75 µs at VIN = 10 V, RON = 200 kΩ) sets switching frequency in continuous conduction mode.

It integrates a high-side N-MOSFET (RDS-ON = 0.7 Ω typ), bootstrap gate driver (BOOT–SW UVLO at 1.7–4 V), internal 7-V linear regulator (VCC), and dual protection comparators: cycle-by-cycle current limit (735 mA typ) and output overvoltage/overcurrent detection at 300 mV on CS.

Key Specifications

Pinout & Package

LM3402MM is housed in an 8-pin VSSOP (DGK) package measuring 3.00 mm × 3.00 mm with exposed thermal pad (DAP) for enhanced thermal performance. The DAP must be soldered to PCB ground plane using 4–6 thermal vias.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM3402MM, LM3402MMX/NOPB offers identical performance in production-ready packaging, while MPQ4425AGU-AEC1-P provides higher current and automotive qualification at the cost of added complexity and non-pin-compatible layout.

Availability

LM3402MM is available at Aetrix Electronics and suitable for automotive lighting, industrial area illumination, and commercial signage applications requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LM3402MM 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 technologies, with leadership in high-reliability industrial and automotive ICs.

The LM3402MM belongs to TI's LED driver product line, engineered for robust, low-component-count constant-current regulation in harsh environments-prioritizing thermal resilience, fault tolerance, and ease of system integration.

FAQ

What is the maximum LED string voltage supported by the LM3402MM?

The LM3402MM's maximum output voltage VO(MAX) is determined by its 300 ns minimum OFF-time and input voltage: VO(MAX) ≈ VIN × tON / (tON + 300 ns). At VIN = 42 V and typical tON = 650 ns (LM3402), VO(MAX) reaches ~29 V. This supports up to six 4.5-V white LEDs in series. Exceeding VO(MAX) risks unregulated operation or open-LED fault triggering.

Can the LM3402MM operate without an output capacitor?

Yes, the LM3402MM supports capacitor-less operation because it regulates LED current-not voltage-and the inductor directly controls current ripple. A small 10-nF capacitor across the LED string dampens ringing. When using no output capacitor, ensure the LED string's total forward voltage stays well below VO(MAX) to avoid instability during transients.

How does the RON pin set switching frequency in the LM3402MM?

The RON pin connects to an external resistor between RON and VIN. This resistor programs the controlled ON-time (tON) per cycle: tON ≈ 1.34×10⁻¹⁰ × RON / VIN. Since tOFF-MIN is fixed at 300 ns, switching frequency fSW ≈ 1 / (tON + 300 ns). For example, RON = 200 kΩ at VIN = 24 V yields tON ≈ 560 ns and fSW ≈ 1.16 MHz.

Does the LM3402MM require a heatsink in standard applications?

Not typically. With RθJB = 25.8°C/W and 0.7 Ω RDS-ON, the LM3402MM dissipates ~175 mW at 500 mA and VIN = 24 V (assuming 3 V LED drop). Junction rise is ~4.5°C above board temperature-well within limits. However, in enclosed fixtures or at high ambient temperatures (>85°C), thermal vias under the DAP and copper pour are strongly recommended.

What protection features does the LM3402MM include?

The LM3402MM integrates cycle-by-cycle current limiting (735 mA typ), thermal shutdown (165°C), input UVLO (5.25 V), BOOT UVLO (1.7–4 V), and output overvoltage/overcurrent protection via the CS pin (300 mV threshold). It also supports open-LED detection using external Zener clamping and provides hiccup-mode recovery during persistent overloads.