onsemi MMSZ5240B

Overview

MMSZ5240B from Fairchild Semiconductor is a 5% tolerance, 500 mW surface-mount Zener diode with nominal zener voltage of 10.0 V at 5.0 mA test current, dynamic impedance of 17 Ω at 5.0 mA, and reverse leakage current ≤0.25 µA at 8.0 V. It operates in SOD-123 package and serves as a precision voltage reference or overvoltage clamp in low-power analog and power management circuits.

For engineers reviewing the MMSZ5240B datasheet, pinout, applications, or equivalent options, key selection criteria include its 10.0 V nominal zener voltage, 17 Ω zener impedance at 5 mA, 500 mW power rating, SOD-123 footprint compatibility, and thermal resistance of 340°C/W - all critical for stable biasing and regulation in space-constrained designs.

Technical Context

The MMSZ5240B functions as a silicon planar Zener diode operating in reverse breakdown mode, delivering stable voltage regulation across a 1.0–20 mA zener current range. Its 10.0 V nominal zener voltage is specified at 5.0 mA with ±5% tolerance, and it exhibits a temperature coefficient near zero around this voltage point.

Designed for DC voltage reference and transient suppression, the device maintains ≤0.25 µA reverse leakage at VR = 8.0 V and supports forward conduction with VF ≤ 0.9 V at IF = 10 mA. Its SOD-123 package enables automated placement in compact PCB layouts while meeting industrial storage (−55°C to +150°C) and junction temperature (up to +150°C) requirements.

Key Specifications

Pinout & Package

SOD-123 package: 2-terminal surface-mount diode with cathode band marking; dimensions 2.7 × 1.6 × 1.1 mm; optimized for high-density PCB assembly and thermal performance on FR-4 substrates.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BZX584C10 and 1N4740A, the MMSZ5240B uniquely balances 500 mW capability, SOD-123 manufacturability, and 17 Ω impedance - making it optimal for modern SMT-based voltage references where thermal and layout constraints exclude both ultra-miniature and through-hole alternatives.

Availability

MMSZ5240B is available at Aetrix Electronics and suitable for industrial sensor conditioning, USB port protection, microcontroller reset circuits, and DC-DC feedback networks requiring stable component supply and consistent parametric performance across production lots.

Supply support for MMSZ5240B 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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, analog, and discrete devices before its acquisition by ON Semiconductor in 2016.

The MMSZ52xxB series was developed for high-reliability, low-cost voltage regulation in space-constrained consumer, computing, and industrial electronics - emphasizing tight tolerance, stable impedance, and SMT manufacturability.

FAQ

What is the nominal zener voltage and test condition for MMSZ5240B?

The MMSZ5240B has a nominal zener voltage of 10.0 V, specified at a test current of 5.0 mA with ±5% tolerance. This value is measured under standard conditions (T_A = 25°C) and reflects the voltage across the device when operating in reverse breakdown. The MMSZ5240B maintains this regulation point with low dynamic impedance (17 Ω), ensuring stable performance in reference and clamp applications where precision matters.

Can MMSZ5240B be used in place of a 1N4740A?

The MMSZ5240B and 1N4740A share identical 10.0 V nominal zener voltage and ±5% tolerance, but differ critically in package and power rating: MMSZ5240B uses SOD-123 (500 mW), while 1N4740A uses DO-41 (1 W). The MMSZ5240B is not a drop-in replacement due to footprint incompatibility and lower power handling. Use MMSZ5240B only in SMT designs where 500 mW suffices and board layout matches SOD-123 land patterns.

What is the maximum reverse leakage current for MMSZ5240B and at what voltage is it specified?

The MMSZ5240B specifies a maximum reverse leakage current of 0.25 µA at V_R = 8.0 V, measured at T_A = 25°C. This low leakage ensures minimal parasitic current draw in high-impedance bias networks and battery-sensitive applications. The MMSZ5240B maintains this specification across its qualified temperature range, supporting reliable operation in sensor interfaces and low-power reset circuits where signal integrity depends on negligible off-state conduction.

Does MMSZ5240B have a specified forward voltage, and how is it relevant?

Yes, the MMSZ5240B has a maximum forward voltage (V_F) of 0.9 V at I_F = 10 mA. While primarily used in reverse-bias Zener mode, this forward characteristic enables dual-use in polarity-sensitive protection schemes - for example, as a series-connected clamp against negative transients or as part of bidirectional TVS configurations. The MMSZ5240B's low V_F ensures minimal voltage drop when conducting forward current, preserving signal margins in mixed-mode protection designs.

What is the thermal resistance and maximum junction temperature for MMSZ5240B?

The MMSZ5240B has a junction-to-ambient thermal resistance (R_θJA) of 340°C/W under standard FR-4 mounting conditions, and a maximum operating junction temperature (T_J) of +150°C. These values define safe operating limits: at 500 mW dissipation, junction temperature rise is ~170°C above ambient - meaning derating is required above ~25°C ambient to stay within the +150°C limit. The MMSZ5240B's thermal specs guide layout decisions such as copper pour area and airflow requirements in thermally demanding applications.