Microchip Technology 1N4745AUR/TR

Overview

1N4745AUR/TR from Microsemi is a surface-mount 1.0 W glass-encapsulated Zener diode with a nominal Zener voltage of 16 V ±5%, 15.5 mA test current, 16 Ω dynamic impedance at I_ZT, and maximum reverse leakage of 5 µA at 12.2 V. It operates from –65 °C to +175 °C and is used for precision voltage regulation in high-density power supply feedback loops and reference circuits.

For engineers reviewing the 1N4745AUR/TR datasheet, 1N4745AUR/TR pinout, 1N4745AUR/TR application, or 1N4745AUR/TR equivalent, key selection criteria include Zener tolerance (±5%), thermal resistance (130 °C/W on FR4), surge current rating (700 mA), low capacitance, and hermetic DO-213AB MELF packaging for reliability-critical analog and industrial systems.

Technical Context

This device functions as a two-terminal voltage reference diode operating in reverse breakdown. Its Zener voltage is specified at 30 °C with 90-second stabilization, and its knee impedance (57 Ω at 0.25 mA) ensures stable regulation at low currents. The glass MELF package provides hermetic sealing and inherent radiation hardness per MicroNote 050.

It delivers regulated output across a broad current range (0.25 mA to 700 mA) with minimal temperature drift and is electrically equivalent to through-hole 1N4745A but packaged in JEDEC DO-213AB for SMT assembly. RoHS-compliant matte-tin terminations support lead-free reflow up to 260 °C for 10 seconds.

Key Specifications

Pinout & Package

Package: DO-213AB glass MELF - hermetically sealed, leadless cylindrical surface-mount package with cathode band marking; dimensions: Ø2.39–2.66 mm × 4.80–5.20 mm length; weight: 0.05 g.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 1N4745A and SMAJ4745A, the 1N4745AUR/TR offers superior thermal performance in SMT layouts, guaranteed hermeticity for long-term stability, and native compatibility with tape-and-reel automated placement-making it optimal for mission-critical, high-reliability embedded power regulation.

Availability

1N4745AUR/TR is available at Aetrix Electronics and suitable for industrial power supplies, automotive engine control units, and medical instrumentation requiring stable component supply, long-lifecycle availability, and traceable sourcing.

Supply support for 1N4745AUR/TR 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

Microsemi (now part of Microchip Technology) is a U.S.-based semiconductor company specializing in high-reliability analog, RF, and timing solutions for aerospace, defense, and industrial markets.

The 1N47xxAUR series was designed specifically for surface-mount voltage regulation in high-density, high-reliability systems where hermetic sealing, radiation tolerance, and wide temperature operation are mandatory.

FAQ

What is the Zener voltage tolerance of the 1N4745AUR/TR?

The 1N4745AUR/TR has a nominal Zener voltage of 16 V with a tolerance of ±5%, indicated by the "A" suffix in the part number. This tolerance is verified at 30 °C with 90-second stabilization per the Microsemi datasheet. Tighter tolerances (±2% or ±1%) are available with "C" or "D" suffixes, but the 1N4745AUR/TR specifically uses the "A" grade. Its regulation stability supports mid-precision feedback loops without post-manufacturing calibration.

Is the 1N4745AUR/TR compatible with lead-free reflow soldering?

Yes, the 1N4745AUR/TR features RoHS-compliant annealed matte-tin terminations and is rated for lead-free reflow soldering at 260 °C for up to 10 seconds, per MIL-STD-750 Method 2026. Its DO-213AB glass MELF body withstands thermal shock during reflow, and the 0.05 g mass ensures uniform heating. This makes the 1N4745AUR/TR suitable for modern SMT lines without requiring special profile adjustments beyond standard Pb-free settings.

What is the maximum steady-state power dissipation for the 1N4745AUR/TR on a standard FR4 PCB?

The 1N4745AUR/TR delivers 1.00 W steady-state power dissipation when mounted on an FR4 PCB with 1 oz copper and the recommended footprint, provided ambient temperature remains below 45 °C. Its thermal resistance is 130 °C/W junction-to-ambient under those conditions. Derating begins above 45 °C per Figure 1 in the Microsemi datasheet, reaching zero power at 150 °C ambient. This thermal behavior is critical for designing compact power supply feedback networks using the 1N4745AUR/TR.

How does the 1N4745AUR/TR differ from the through-hole 1N4745A?

The 1N4745AUR/TR shares identical electrical specifications-including 16 V Zener voltage, ±5% tolerance, 15.5 mA test current, and 16 Ω dynamic impedance-with the through-hole 1N4745A. However, the 1N4745AUR/TR uses a DO-213AB glass MELF surface-mount package instead of DO-41, enabling higher board density and automated assembly. Its hermetic seal and radiation hardness are intrinsic to the glass construction, whereas the 1N4745A's plastic DO-41 variant lacks these attributes unless specially screened.

What is the surge current rating of the 1N4745AUR/TR and how is it tested?

The 1N4745AUR/TR has a maximum surge current rating of 700 mA, measured using a ½-sine wave pulse of 1/120 second duration at 25 °C ambient, superimposed on the 15.5 mA Zener test current. This rating reflects its ability to absorb transient overvoltages without degradation-critical for protecting downstream circuitry in industrial power supplies. The 1N4745AUR/TR maintains this rating across its full operating temperature range due to its hermetic glass construction and low thermal mass.