Diodes Incorporated FCX558QTA

Overview

FCX558QTA from Diodes Incorporated is a 400V PNP high-voltage bipolar junction transistor (BJT) in SOT89 package, rated for -400V V_CEO, -200mA continuous collector current, and qualified to AEC-Q101 for automotive use. It delivers low saturation voltage (< -200mV @ -20mA), excellent h_FE up to -100mA, and operates across -65°C to +150°C for under-hood power switching.

For engineers reviewing the FCX558QTA datasheet, FCX558QTA pinout, FCX558QTA application, or FCX558QTA equivalent, key selection criteria include high-voltage blocking capability, thermal performance on 15mm×15mm copper, complementary pairing with FCX458, and PPAP-capable automotive qualification status.

Technical Context

This PNP BJT is engineered for high-reliability automotive power control circuits where sustained 400V reverse bias and robust pulse handling (-500mA I_CM) are required. Its low V_CE(sat) and stable h_FE over -1mA to -100mA support efficient linear and switching operation in load dump protection and ignition drivers.

Thermal design relies on the exposed collector pad: R_θJL = 22°C/W enables direct heat transfer to PCB copper, while R_θJA varies from 178°C/W (MRP) to 60°C/W (50mm×50mm 1oz Cu), making layout-dependent derating essential for >0.7W steady-state dissipation.

Key Specifications

Pinout & Package

SOT89 package with exposed collector pad for thermal management; molded green plastic case (UL 94V-0), matte tin-plated leads, 0.05g weight.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage PNP transistor applications.

Compared with ZTX653 and BCX56-16, FCX558QTA uniquely combines AEC-Q101 qualification, -400V blocking, and SOT89 thermal performance-making it the only option among the three for automotive-grade high-voltage PNP switching where space, reliability, and transient immunity are jointly constrained.

Availability

FCX558QTA is available at Aetrix Electronics and suitable for automotive load dump protection, ignition coil drivers, and industrial relay output stages requiring stable component supply with full traceability and lifecycle management.

Supply support for FCX558QTA 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 components for automotive, industrial, and computing markets.

The FCX558QTA belongs to Diodes' automotive-qualified bipolar transistor product line, designed specifically for high-voltage power switching in harsh-environment applications such as engine control, body electronics, and chassis systems.

FAQ

What is the maximum allowable PCB copper area for FCX558QTA to achieve 2.0W pulse power dissipation?

The 2.0W pulse power rating is specified when the exposed collector pad is mounted on a 50mm×50mm 1oz copper area on FR4 PCB, per Note 9 in the Absolute Maximum Ratings table. Smaller copper areas reduce achievable pulse power: 25mm×25mm yields 1.5W, 15mm×15mm yields 1.0W, and minimum recommended pad layout yields 0.7W. Thermal simulation or empirical testing is recommended for custom layouts.

Can FCX558QTA be used in linear regulator applications?

Yes, but with strict thermal constraints: its V_CE(sat) is optimized for switching, not linear operation. At I_C = -100mA and V_CE = -10V, power dissipation reaches 1.0W-requiring ≥25mm×25mm copper to stay within safe junction temperature. Linear use is discouraged unless thermal margins are verified per the derating curves in Figures 3–4 of DS39500.

Is FCX558QTA pin-compatible with FCX458?

No-FCX558QTA (PNP) and FCX458 (NPN) have complementary polarity but identical SOT89 pinout: Collector (exposed pad), Emitter, Base in same physical order. However, circuit topology must invert (e.g., high-side vs. low-side switching), and base drive polarity must be reversed. They are functionally paired, not drop-in replacements.

Does FCX558QTA require a heatsink for 1.0W continuous operation?

No external heatsink is needed if mounted per the 15mm×15mm 1oz copper recommendation: R_θJA = 125°C/W at TA = +25°C yields ~125°C junction rise above ambient, resulting in TJ ≈ 150°C-within the -65°C to +150°C rating. Operation above +25°C ambient requires derating per Figure 3; at +70°C ambient, max continuous power drops to ~0.6W without additional copper area.