Diodes Incorporated ZXLD1937ET5TA

Overview

ZXLD1937ET5TA from Diodes Incorporated (formerly Zetex) is a PFM inductive boost converter IC designed to drive 2–4 white LEDs in series from a Li-ion cell (2.5–5.5V), or up to 8 LEDs from a 5V supply. It integrates an NDMOS switch, peak current sense resistor, and internal PWM low-pass filter; delivers up to 50mA output current with 28V max output voltage, 60µA typical quiescent current, and operates in discontinuous conduction mode.

For engineers reviewing the ZXLD1937ET5TA datasheet, ZXLD1937ET5TA pinout, ZXLD1937ET5TA application, or ZXLD1937ET5TA equivalent, key selection criteria include its TSOT23-5 package height (<1mm), true analog dimming via EN-pin PWM filtering (4kHz cutoff), 320mA internal peak current limit, 100mV FB reference for precise current setting, and inherent LED current matching across parallel strings.

Technical Context

The ZXLD1937ET5TA implements a self-oscillating PFM control loop that regulates LED current by sensing voltage across an external sense resistor at the FB pin against a 100mV internal reference. Switching frequency varies dynamically (350kHz–1MHz) with load and input conditions to maintain efficiency in discontinuous mode.

Its EN pin serves dual functions: digital enable/disable control and analog dimming interface-internally routing PWM signals through a 4kHz low-pass filter to generate a DC-equivalent control voltage. The device features 120µs turn-off delay to sustain output during high-frequency PWM gating and includes open-circuit protection support via external Zener clamping.

Key Specifications

Pinout & Package

Supplied in a space-constrained TSOT23-5 package with maximum 1.00mm height, optimized for portable backlight applications. Pin assignments are validated per Zetex Issue 1 (July 2004) datasheet and confirmed on official Diodes Incorporated product page.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZXLD1937ET5TA, AP5724WUG-7 trades integrated dimming simplicity for higher peak current headroom, while AL8805W5-7 expands input range and output capability at the cost of external sensing and larger solution size.

Availability

ZXLD1937ET5TA is available at Aetrix Electronics and suitable for mobile phone backlighting, digital camera displays, PDA keypad illumination, and portable internet appliance UI panels requiring stable component supply with long-lifecycle support.

Supply support for ZXLD1937ET5TA 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 acquired Zetex Semiconductors in 2008 and maintains its portfolio of high-performance analog and power management ICs targeting portable and battery-operated applications.

The ZXLD1937 belongs to Zetex's legacy LED driver product line, engineered specifically for ultra-thin, low-power backlight solutions in consumer handhelds where board height and quiescent current are critical constraints.

FAQ

What is the recommended inductor value for ZXLD1937ET5TA?

The datasheet specifies 6.8µH to 22µH as the optimal inductor range. A 10µH inductor (e.g., Coilcraft DO1608-103) is most commonly used, balancing switching frequency (~600kHz), efficiency (>80%), and physical size. Lower values increase frequency and switching losses; higher values risk violating the 5µs maximum on-time limit under low-VIN conditions.

How do I calculate the FB resistor for a target LED current?

Use R1 = 100mV / I_LED. For example, 15mA requires R1 = 100mV / 0.015A = 6.67kΩ → standard 6.8kΩ. Tolerance directly impacts current accuracy: ±1% R1 yields ±1% I_LED, since V_FB is trimmed to ±9.5% over temperature.

Can ZXLD1937ET5TA drive more than 4 white LEDs from a Li-ion source?

No-when powered from a Li-ion cell (max 4.2V), the 28V output limit supports only up to 4 white LEDs (3.2V × 4 = 12.8V forward drop, plus margin). Driving 8 LEDs requires a 5V supply, as stated in the device description; attempting 5+ LEDs from Li-ion risks insufficient headroom for regulation.

Is external open-circuit protection required?

Yes-while the device limits output voltage to 28V, sustained open-circuit conditions can exceed this if inductor energy is not safely dissipated. A Zener diode rated slightly above the LED string's total V_F (e.g., 15V for 4×3.2V) must be placed across the LED chain to clamp LX voltage and protect the internal switch.