Diodes Incorporated ZXSC310EV

Overview

ZXSC310EV from Zetex Semiconductors is a PFM-based DC-DC controller IC designed to drive external NPN switching transistors in LED backlighting circuits. It operates from 0.8V to 8V input, delivers constant-power output via programmable current sense (19mV threshold), supports shutdown mode (<5µA standby), and targets LCD backlights in digital still cameras and PDAs using SOT23-5 packaging.

For engineers reviewing the ZXSC310EV datasheet, ZXSC310EV pinout, ZXSC310EV application, or ZXSC310EV equivalent, key selection criteria include minimum startup voltage (0.8V), ISENSE threshold accuracy (14–24mV), VDRIVE drive capability (1.5–3.5mA), thermal limits (−40°C to +85°C), and compatibility with low-V_CE(sat) transistors like FMMT618.

Technical Context

The ZXSC310EV implements a pulse-frequency modulation (PFM) control architecture with an internal comparator monitoring ISENSE voltage against a 19mV reference. When the sense resistor voltage exceeds this threshold, the monostable circuit forces a fixed 1.2–3.2µs discharge time (T_DRV) to ensure inductor reset before next cycle.

Its VDRIVE output supplies fixed-current base drive (1.5–3.5mA) to an external NPN transistor, enabling fast turn-off (~30ns) and minimizing conduction loss. Startup occurs at 0.8V under full load, and efficiency peaks at 94% with optimized external components including Schottky diodes (e.g., ZHCS1000) and 68µH inductors.

Key Specifications

Pinout & Package

SOT23-5 package: 2.8mm × 2.6mm body, 0.95mm pitch, 5-pin single-row outline with exposed pad not present; RoHS-compliant, lead-free finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX1910 and TPS61060, the ZXSC310EV uniquely supports 0.8V startup and delivers higher efficiency in ultra-low-voltage battery applications through its PFM architecture and external transistor optimization-critical for legacy single-cell portable devices where every millivolt matters.

Availability

ZXSC310EV is available at Aetrix Electronics and suitable for LCD backlighting in digital still cameras, PDA displays, and mobile phone keypad illumination requiring stable component supply across extended production lifecycles.

Supply support for ZXSC310EV 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

Zetex Semiconductors (now part of Diodes Incorporated) is a UK-based designer of high-performance analog and discrete semiconductors, ISO 9001/TS16949 certified, focused on power efficiency and miniaturization.

The ZXSC310EV belongs to Zetex's LED driver controller product line, engineered specifically for cost-sensitive, battery-powered LCD backlight applications demanding ultra-low-voltage operation and high conversion efficiency.

FAQ

What external components are mandatory for basic ZXSC310EV operation?

The ZXSC310EV requires three mandatory external components: an NPN switching transistor (e.g., FMMT618) connected to VDRIVE and ISENSE, a current-sense resistor tied between ISENSE and GND to set LED current, and an inductor between VCC and the transistor collector. No input/output capacitors are strictly required for pulsed operation, though a 470nF–1µF ceramic cap on VCC improves EMC.

How does the 19mV ISENSE threshold translate to actual LED current?

LED current is calculated as I_LED ≈ 19mV / R_SENSE. For example, a 150mΩ resistor yields ~127mA peak current, while a 1.0Ω resistor sets ~19mA. The actual average current depends on duty cycle and topology (pulsed vs. rectified), and temperature drift is ±0.4%/°C across −40°C to +85°C.

Can ZXSC310EV drive multiple parallel LED strings?

Yes - the ZXSC310EV regulates total output power, not per-string current. To drive parallel strings, connect them to a common output node after the Schottky diode and output capacitor (in rectified mode), ensuring matched forward voltages or adding individual current-limiting resistors to prevent current imbalance and thermal runaway.

Why does ZXSC310EV use PFM instead of PWM control?

PFM operation allows the ZXSC310EV to maintain high efficiency (up to 94%) across wide load ranges and ultra-low input voltages (down to 0.8V) by varying switching frequency rather than duty cycle. This avoids inefficient light-load PWM operation and eliminates need for complex compensation networks, simplifying design for portable battery-powered systems.