Diodes Incorporated MMSZ5257B-7-F

Overview

MMSZ5257B-7-F from Diodes Incorporated is a 33 V, 500 mW surface-mount Zener diode in SOD123 package, rated for 3.8 mA test current with 58 Ω dynamic impedance at 1 kHz and 0.1 µA reverse leakage at 25 V, used for precision voltage regulation and reference in low-power analog circuits.

For engineers reviewing the MMSZ5257B-7-F datasheet, MMSZ5257B-7-F pinout, MMSZ5257B-7-F application, or MMSZ5257B-7-F equivalent, key selection criteria include nominal Zener voltage tolerance (±3.5%), thermal resistance (338 °C/W), AEC-Q101 qualification status, and SOD123 footprint compatibility with automated assembly.

Technical Context

This Zener diode operates in reverse breakdown to maintain stable voltage across its terminals under varying load and temperature conditions. Its 33 V nominal Zener voltage exhibits a positive temperature coefficient of +0.07 %/°C, and it delivers regulated output within ±3.5% tolerance over the full operating range.

The device is optimized for low-current reference applications, with specified performance at I_ZT = 3.8 mA and I_ZK = 0.25 mA. It features a cathode band polarity marker and is qualified to AEC-Q101 for automotive-grade reliability.

Key Specifications

Pinout & Package

Package: SOD123 - surface-mount plastic case with matte tin-plated alloy 42 leadframe, 0.01 g mass, UL 94V-0 flammability rating, and moisture sensitivity level 1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BZX584-C33 and MMBZ5257B, MMSZ5257B-7-F offers superior thermal derating (370 mW vs. 300 mW) and AEC-Q101 qualification, making it preferred for automotive and industrial designs requiring long-term stability under thermal stress.

Availability

MMSZ5257B-7-F is available at Aetrix Electronics and suitable for automotive sensor interfaces, industrial power supply feedback loops, and portable instrumentation biasing requiring stable component supply and AEC-Q101 compliance.

Supply support for MMSZ5257B-7-F 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, headquartered in Plano, Texas, with design, manufacturing, and sales operations across Asia, Europe, and North America.

The MMSZ52xxB series belongs to Diodes' general-purpose Zener diode product line, engineered for cost-effective, high-reliability voltage regulation in automotive, industrial, and consumer power management systems.

FAQ

What is the maximum reverse voltage this Zener diode can withstand before breakdown?

The MMSZ5257B-7-F has a nominal Zener voltage of 33 V with a guaranteed range of 31.35 V to 34.65 V at 3.8 mA test current. Its reverse breakdown is sharply defined within this band; operation below 31.35 V results in negligible conduction (<0.1 µA at 25 V), and exceeding 34.65 V risks exceeding safe power limits unless current is strictly limited.

Is this part suitable for automotive applications?

Yes - MMSZ5257B-7-F is explicitly qualified to AEC-Q101 standards, confirming its suitability for automotive applications including engine control units, body electronics, and ADAS sensor interfaces. It operates reliably from −65°C to +150°C and meets stringent reliability, thermal cycling, and humidity testing requirements defined in the AEC specification.

How does the SOD123 package affect PCB layout and thermal performance?

The SOD123 package uses a 1.55 mm × 2.65 mm footprint with 0.57 mm lead width and requires a recommended pad layout of 0.9 mm × 0.95 mm (X × Y). Its R_θJA of 338 °C/W assumes a 1-inch² copper pad on FR-4; reducing pad area increases thermal resistance, so thermal relief must be minimized and adjacent copper pours maximized for high-duty-cycle operation.

Can this Zener diode replace older MMSZ5257 versions without design changes?

Yes - MMSZ5257B-7-F is a direct replacement for prior revisions of MMSZ5257 (e.g., non-B suffix variants), retaining identical electrical characteristics, SOD123 mechanical dimensions, and marking format. The "B" suffix denotes tighter Zener voltage tolerance (±3.5% vs. ±5% in earlier versions), and the "-7-F" denotes 3,000-piece tape-and-reel packaging with lead-free plating.