onsemi MMSZ5239B

Overview

MMSZ5239B from ON Semiconductor (formerly Fairchild) is a 9.1 V, 5% tolerance Zener diode in SOD-123 package, rated for 500 mW power dissipation and 10 Ω dynamic impedance at 5 mA test current, used for precision voltage regulation and reference in low-power analog circuits, power supply feedback loops, and overvoltage protection.

For engineers reviewing the MMSZ5239B datasheet, pinout, applications, or equivalent options, key selection criteria include its 9.1 V nominal Zener voltage with ±5% tolerance, 10 Ω Zener impedance at I_Z = 5 mA, 0.25 µA maximum reverse leakage at 7.0 V, 600 Ω impedance at knee current, and thermal resistance of 340°C/W - all critical for stable reference design under varying load and temperature.

Technical Context

The MMSZ5239B operates as a silicon planar Zener diode optimized for stable voltage reference generation in low-current (<20 mA) applications. Its 9.1 V breakdown voltage is specified at I_Z = 5 mA, with typical Zener impedance of 10 Ω and maximum of 17 Ω, ensuring tight regulation across operating conditions.

It features a forward voltage ≤0.9 V at 10 mA, operates from –55°C to +150°C junction temperature, and maintains <0.25 µA reverse leakage at 7.0 V - enabling reliable performance in battery-powered and industrial sensor interfaces where low standby current and thermal stability are essential.

Key Specifications

Pinout & Package

SOD-123 package: two-terminal device with cathode marked by band; no internal leads - anode and cathode connect directly to PCB pads per JEDEC MO-202 standard.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BZX584C9V1 and MM3Z9V1T1G, the MMSZ5239B delivers superior thermal performance (500 mW vs. ≤350 mW), lower Zener impedance (10 Ω vs. ≥15 Ω), and proven stability in industrial feedback loops - making it the preferred choice for sustained 5–20 mA reference applications requiring long-term voltage accuracy.

Availability

MMSZ5239B is available at Aetrix Electronics and suitable for power supply feedback, microcontroller reset circuits, overvoltage clamping, and ADC reference stabilization requiring stable component supply and consistent parametric performance across production batches.

Supply support for MMSZ5239B 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

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

The MMSZ5239B belongs to the MMSZ52xxB family of precision Zener diodes designed specifically for low-power voltage reference and regulation in space-constrained, thermally demanding PCB environments.

FAQ

What is the nominal Zener voltage and tolerance of the MMSZ5239B?

The MMSZ5239B has a nominal Zener voltage of 9.1 V with a ±5% tolerance, specified at a test current of 5 mA. This means the actual breakdown voltage falls between 8.645 V and 9.555 V under standard conditions. The MMSZ5239B achieves this tight tolerance through process-controlled silicon doping and post-trim testing, making it suitable for applications requiring predictable voltage clamping without external adjustment.

What is the maximum power dissipation and thermal resistance of the MMSZ5239B?

The MMSZ5239B is rated for 500 mW maximum power dissipation at 25°C ambient temperature, with a junction-to-ambient thermal resistance (R_θJA) of 340°C/W. This value assumes use of minimum recommended land pads on FR-4 PCB. At 500 mW, the junction temperature rise is approximately 170°C above ambient - so operation at full rating requires ambient ≤–20°C or derating above 25°C. The MMSZ5239B must be thermally managed accordingly in enclosed or high-temperature environments.

What is the Zener impedance of the MMSZ5239B and why does it matter?

The MMSZ5239B exhibits a typical Zener impedance (Z_Z) of 10 Ω at 5 mA test current, with a maximum of 17 Ω. This low dynamic impedance ensures minimal change in output voltage under varying load currents - for example, a ±1 mA shift causes only ±10 mV deviation. In shunt regulator or reference applications, this directly translates to improved line and load regulation. The MMSZ5239B's 10 Ω Z_Z is significantly lower than many general-purpose Zeners, supporting higher accuracy in precision analog circuits.

Can the MMSZ5239B be used in reverse-bias overvoltage protection circuits?

Yes, the MMSZ5239B is routinely used in reverse-bias overvoltage protection due to its well-defined 9.1 V breakdown and 500 mW surge capability. When placed across a sensitive node with appropriate series current limiting, it clamps transients to ≤9.1 V + forward drop of any series diode. Its 0.25 µA leakage at 7.0 V ensures negligible standby current, and its 600 Ω impedance at knee current (I_ZK) enables reliable turn-on during slow-rising faults. The MMSZ5239B performs reliably in such roles when current is limited to avoid exceeding its SOA.

What is the forward voltage specification for the MMSZ5239B?

The MMSZ5239B has a maximum forward voltage (V_F) of 0.9 V at 10 mA forward current, consistent across the entire MMSZ5200 series. This parameter is relevant when the device is used in forward-conduction mode - for example, as a polarity protection diode or in bidirectional transient suppressor configurations. Unlike its Zener behavior, forward conduction is not its primary function, but the guaranteed ≤0.9 V drop supports predictable voltage drop modeling in dual-role protection schemes involving the MMSZ5239B.