Texas Instruments LM3405XMK

Overview

LM3405XMK from Texas Instruments is a 1.6-MHz, 1-A constant-current buck LED driver in a 6-pin SOT-23 (DDC) package. It regulates LED current via 0.205-V feedback reference, supports PWM dimming via EN/DIM pin, and integrates a 300-mΩ NMOS switch for driving up to five high-brightness LEDs in series - used in portable LED flashlights and industrial lighting systems.

For engineers reviewing the LM3405XMK datasheet, LM3405XMK pinout, LM3405XMK application, or LM3405XMK equivalent, key selection criteria include its 3–15 V input range, 1.6 MHz fixed-frequency operation enabling compact magnetics, thermal shutdown at 165°C, cycle-by-cycle current limit, and 0.3 µA shutdown quiescent current - all critical for battery-powered and thermally constrained LED designs.

Technical Context

The LM3405XMK employs current-mode control with internal compensation and a fixed 1.6-MHz oscillator, eliminating external frequency-setting components. Its feedback loop maintains LED current by regulating FB pin voltage to 0.205 V using an external sense resistor.

It features integrated boost circuitry requiring a bootstrap capacitor between BOOST and SW pins to generate ≥2.5 V gate drive above SW, enabling low R_DS(ON) switching. Protection includes undervoltage lockout (2.74 V rising threshold), overcurrent detection (328 mV FB threshold), and thermal shutdown (165°C trip).

Key Specifications

Pinout & Package

LM3405XMK is housed in a 6-pin SOT-23 (DDC) package measuring 2.90 mm × 1.60 mm, optimized for space-constrained LED driver layouts with exposed pad for thermal relief.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM3405XMK, LM3404MHX/NOPB offers greater current headroom and superior thermal dissipation but requires more PCB area; TPS92515HVDGQR provides higher switching frequency and integrated current sensing at the cost of increased complexity and price - making LM3405XMK optimal for cost-sensitive, space-constrained 1-A LED applications.

Availability

LM3405XMK is available at Aetrix Electronics and suitable for portable LED flashlights, industrial panel lighting, and automotive interior lighting requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LM3405XMK 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 broad industrial and automotive design expertise.

The LM3405XMK belongs to TI's LED driver product line, engineered specifically for efficient, compact, and reliable constant-current regulation in portable and medium-power LED lighting applications.

FAQ

What is the recommended minimum and maximum external sense resistor value for LM3405XMK?

The LM3405XMK uses a 0.205-V internal reference to set LED current via R1 = V_FB/I_F. To ensure stable regulation and stay within the device's 1-A capability, R1 must be between 0.205 Ω (for 1 A) and 1.025 Ω (for 200 mA minimum stable current). Values outside this range risk instability or current-limit activation. Always verify thermal derating at elevated ambient temperatures.

Can LM3405XMK drive more than five LEDs in series?

LM3405XMK can drive up to five high-brightness LEDs in series at 1 A only if total forward voltage remains ≤ (VIN_MAX – V_D1 – I_F × R_DS(ON)). With VIN = 15 V, typical V_F = 3.7 V per LED, and V_D1 ≈ 0.5 V, five LEDs require ~19 V - exceeding practical limits. Driving six or more LEDs typically requires higher VIN or a different topology; LM3405XMK is not rated for such configurations.

How does the BOOST pin function in LM3405XMK, and what capacitor value is recommended?

The BOOST pin supplies gate drive voltage to the internal NMOS switch via a bootstrap capacitor connected to SW. A 0.1-µF ceramic capacitor (X7R, 16-V rating) is recommended between BOOST and SW. This capacitor must sustain ≥2.5 V above SW during on-time; insufficient capacitance causes R_DS(ON) increase and efficiency loss. Layout must minimize trace inductance between BOOST, SW, and the capacitor.

Does LM3405XMK support analog dimming, or only PWM dimming via the EN/DIM pin?

LM3405XMK supports only PWM dimming via the EN/DIM pin - it does not provide analog (DC) dimming capability. The EN/DIM pin toggles the regulator fully on/off at frequencies from 100 Hz to 5 kHz; average LED current scales linearly with duty cycle. Analog dimming would require external circuitry to modulate the FB reference or sense resistor, which is unsupported and invalidates regulation accuracy.

What is the thermal resistance (θ_JA) of LM3405XMK in its SOT-23 package, and how does it affect maximum output current?

LM3405XMK in the DDC (SOT-23-6) package has θ_JA = 182.9°C/W. At 125°C max junction temperature and 25°C ambient, allowable power dissipation is ~0.55 W. With 1-A output and 300-mΩ R_DS(ON), conduction loss alone is 0.3 W - leaving limited margin for switching losses and ambient rise. For sustained 1-A operation, PCB copper area and airflow must be optimized; derating is required above 60°C ambient.