onsemi BZX84C18LT3

Overview

BZX84C18LT3 from onsemi is a 18 V, ±5% tolerance Zener diode in SOT-23 package, rated for 225 mW power dissipation on FR-5 board at 25°C, with 45 Ω dynamic impedance at 5 mA test current and 0.05 µA reverse leakage at 14.4 V. It provides precision voltage regulation in space-constrained portable electronics such as smartphone power rail clamping and battery protection circuits.

For engineers reviewing the BZX84C18LT3 datasheet, pinout, applications, or equivalent options, key selection criteria include Zener voltage tolerance, thermal resistance (556 °C/W), ESD rating (>16 kV HBM), junction temperature range (−65 to +150°C), and SOT-23 mechanical compatibility with automated placement systems.

Technical Context

This device operates as a two-terminal voltage reference using avalanche breakdown in silicon PN junction. Its Zener voltage is specified at three test currents (2 mA, 5 mA, and 20 mA), enabling stable regulation across varying load conditions. The no-connection terminal (Pin 2) isolates internal structure and confirms it is a true two-element Zener, not a dual-diode or transient suppressor.

Temperature coefficient is +12.6 mV/°C at 5 mA, indicating positive drift above 6.2 V nominal - critical for bias network stability over industrial temperature range. Capacitance is 100 pF at 0 V bias and 1 MHz, limiting high-frequency noise filtering capability but suitable for DC/low-speed rail stabilization.

Key Specifications

Pinout & Package

SOT-23 plastic surface-mount package (Case 318, Style 8), void-free thermosetting epoxy body with corrosion-resistant solderable finish; cathode indicated by polarity band; UL 94 V-0 flammability rating; 260°C max soldering temperature for 10 seconds.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar Zener regulation applications.

Compared with BZX84C18LT3, BZX84C18LT1 offers identical performance in smaller reels for flexibility, while BZX84B18LT1 trades wider tolerance for higher precision - making the C-series optimal for cost-sensitive, volume production where ±5% is sufficient.

Availability

BZX84C18LT3 is available at Aetrix Electronics and suitable for smartphone power management, industrial sensor biasing, and automotive body control modules requiring stable component supply with full traceability and long-term lifecycle support.

Supply support for BZX84C18LT3 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The BZX84 series belongs to onsemi's discrete Zener voltage regulator product line, engineered specifically for compact, high-density surface-mount applications where space, reliability, and automated assembly compatibility are critical.

FAQ

What is the Zener voltage tolerance of BZX84C18LT3?

The BZX84C18LT3 has a nominal Zener voltage of 18 V with a tolerance of ±5%, meaning its actual breakdown voltage falls between 16.8 V and 19.1 V when tested at 5 mA. This tolerance is confirmed in the Electrical Characteristics table on page 3 of the official datasheet and applies across the full operating temperature range of −65°C to +150°C. The BZX84C18LT3 uses standard-tolerance grading, distinct from the tighter ±2% BZX84B18LT1 variant.

Does BZX84C18LT3 have a functional third pin?

No, Pin 2 of the BZX84C18LT3 is explicitly designated as "No Connection" in the datasheet's marking diagram and package dimensions section. It is internally unconnected and must remain electrically floating on the PCB - no trace, via, or ground connection should be made to this terminal. The device functions solely as a two-terminal Zener diode between Pin 1 (Anode) and Pin 3 (Cathode).

What is the maximum power dissipation of BZX84C18LT3 on a standard PCB?

The BZX84C18LT3 is rated for 225 mW total power dissipation on FR-5 board at 25°C ambient temperature. Above 25°C, it derates linearly at 1.8 mW/°C, reaching zero dissipation at approximately 153°C ambient. This rating assumes standard JEDEC-defined board layout (1.0 × 0.75 × 0.62 in.) and is validated per the manufacturer's thermal characterization methodology in the Maximum Ratings table.

Can BZX84C18LT3 replace BZX84C18LT1 in existing designs?

Yes, BZX84C18LT3 is a direct form-fit-function replacement for BZX84C18LT1, sharing identical electrical specifications, SOT-23 package dimensions, pinout, and marking. The only difference is packaging: BZX84C18LT3 ships in 10,000-piece 13-inch reels, whereas BZX84C18LT1 uses 3,000-piece 7-inch reels. No PCB or schematic changes are needed when substituting BZX84C18LT3 into designs originally specifying BZX84C18LT1.

What is the temperature coefficient of BZX84C18LT3 and how does it affect circuit performance?

The BZX84C18LT3 has a temperature coefficient of +12.6 mV/°C at 5 mA test current, as specified in the Electrical Characteristics table. This means its Zener voltage increases by approximately 12.6 mV for every 1°C rise in junction temperature. In practice, this positive drift helps counteract negative TC components elsewhere in bias networks, but requires thermal modeling when used in precision references operating across wide ambient ranges.