Diodes Incorporated ZXLD381FHTA

Overview

ZXLD381FHTA from Diodes Incorporated is a PFM-controlled, single-cell LED driver IC with integrated 800 mA low-saturation-voltage switching transistor, designed to boost output from as low as 0.9 V input to drive white LEDs at constant average current (40–70 mA typical) with 85% efficiency and 350 kHz operating frequency. It operates in SOT23-3 package for flashlight, backlight, and portable indicator applications.

For engineers reviewing the ZXLD381FHTA datasheet, ZXLD381FHTA pinout, ZXLD381FHTA application, or ZXLD381FHTA equivalent, key selection criteria include minimum startup voltage (0.9 V), adjustable LED current via external inductor value, VOUT switching capability up to 20 V, and compatibility with alkaline/NiMH/NiCd single cells under full load.

Technical Context

The ZXLD381FHTA implements a pulse-frequency modulation (PFM) control architecture that dynamically adjusts switching frequency based on load and input conditions to maintain constant average LED current. Its internal NPN switch features 100–300 mV saturation voltage at 200 mA, enabling high efficiency even below 1.0 V input.

Energy transfer occurs via discrete charge/discharge cycles: during charge, VOUT is pulled near GND to store energy in the external inductor; during discharge, the switch opens, causing VOUT to rise above VCC and forward-bias the LED. Regulation relies on sensing VOUT decay to zero to trigger the next cycle.

Key Specifications

Pinout & Package

SOT23-3 surface-mount package with 1.12 mm max height, 2.80–3.04 mm length, and 2.10–2.64 mm width; optimized for space-constrained portable lighting designs.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar LED boost driver applications.

Compared with AL8805W50-7 and AP3012KTR-G1, the ZXLD381FHTA uniquely supports sub-1.0 V startup, integrates the power switch, and delivers regulated LED current without sense resistors-making it optimal for cost-sensitive, space-constrained, single-cell flashlight and indicator designs.

Availability

ZXLD381FHTA is available at Aetrix Electronics and suitable for LED flashlights, portable instrument backlights, and emergency exit sign indicators requiring stable component supply and long-term manufacturability.

Supply support for ZXLD381FHTA 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

Diodes Incorporated is a global manufacturer of discrete semiconductors and analog ICs, specializing in high-reliability power management, signal integrity, and protection solutions for consumer, industrial, and automotive markets.

The ZXLD381 belongs to Diodes' LED driver product line, engineered specifically for ultra-low-input-voltage, constant-current boost applications where battery life extension and minimal external components are critical design goals.

FAQ

What is the minimum input voltage required for ZXLD381FHTA to start switching?

The ZXLD381FHTA starts switching at a minimum supply voltage of 0.8 V (typical) and guarantees operation down to 0.9 V under full load with a 10 µH inductor. This enables functionality even with deeply discharged NiMH or alkaline cells, extending usable battery life beyond conventional boost drivers.

How is LED current adjusted without a sense resistor?

LED current is set by the external inductor value: larger inductance yields lower average current (e.g., 22 µH ≈ 20 mA, 4.7 µH ≈ 55 mA at V_LED = 3.5 V). The PFM control loop maintains constant average current by adjusting pulse width and frequency based on inductor energy transfer-no external resistor or feedback path is needed.

Can ZXLD381FHTA drive multiple LEDs in series?

Yes-it supports LED strings up to 20 V total forward voltage, limited by the V_OUT absolute maximum rating. With V_CC = 1.5 V, it can drive three white LEDs (3 × 3.5 V = 10.5 V) or four low-V_F red LEDs (4 × 2.0 V = 8.0 V), provided the inductor and layout accommodate peak switch current and voltage transients.

Is thermal performance affected by the SOT23-3 package in continuous operation?

The SOT23-3 package has a 450 mW power dissipation limit at 25 °C ambient. At full 70 mA LED current and 1.5 V input, power loss remains <100 mW, keeping junction temperature well within the 0–85 °C operating range. No heatsink or airflow is required for standard flashlight or indicator duty cycles.