onsemi MMBZ5251B

Overview

MMBZ5251B from Fairchild Semiconductor is a 22 V, 5% tolerance surface-mount Zener diode in SOT-23 package, rated for 350 mW power dissipation, with 29 Ω dynamic impedance at 5.6 mA test current and 0.1 µA reverse leakage at 17.6 V. It provides precise voltage regulation in low-power biasing and reference circuits.

For engineers reviewing the MMBZ5251B datasheet, pinout, applications, or equivalent options, key selection criteria include its 22 V nominal Zener voltage, ±5% tolerance, 29 Ω Zener impedance, 0.9 V max forward voltage at 10 mA, and SOT-23 thermal performance under 150°C junction temperature limits.

Technical Context

The MMBZ5251B operates as a silicon planar Zener diode optimized for stable voltage reference and overvoltage protection in space-constrained PCB layouts. Its design targets low-current regulation (IZ = 5.6 mA) with tight 5% voltage tolerance and predictable temperature coefficient behavior across –55°C to +150°C operating range.

It features a maximum forward voltage of 0.9 V at 10 mA, reverse leakage of 0.1 µA at VR = 17.6 V, and absolute maximum ratings including 350 mW power dissipation and 150°C junction temperature-enabling use in battery-powered sensors and portable power management rails.

Key Specifications

Pinout & Package

MMBZ5251B is housed in a standard SOT-23 plastic surface-mount package with three terminals. Pin 1 is anode, Pin 2 is cathode, and Pin 3 is not connected (NC), per Fairchild's connection diagram.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BZX84-C22 and MMBZ5251BS, the MMBZ5251B offers optimal balance of low leakage, tight tolerance, and proven thermal reliability in SOT-23 for continuous low-power reference use-while the alternatives address higher-energy clamping or regulatory compliance needs.

Availability

MMBZ5251B is available at Aetrix Electronics and suitable for industrial sensor biasing, USB port overvoltage clamp, and low-power MCU reset circuits requiring stable component supply and long-term obsolescence management.

Supply support for MMBZ5251B 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, signal conditioning, and discrete components before its acquisition by ON Semiconductor in 2016.

The MMBZ52xxB series was developed for compact, high-reliability Zener regulation in consumer, computing, and industrial electronics-emphasizing consistent voltage tolerance, low leakage, and SOT-23 manufacturability.

FAQ

What is the nominal Zener voltage and tolerance of MMBZ5251B?

The MMBZ5251B has a nominal Zener voltage of 22 V with a tolerance of ±5%, measured at a test current of 5.6 mA. This specification is guaranteed across the full operating temperature range and is validated per Fairchild's Rev. A2 datasheet. The MMBZ5251B maintains this voltage accuracy under typical PCB thermal conditions, making it suitable for precision reference applications where tighter tolerances are not required.

What is the maximum power dissipation rating for MMBZ5251B?

The MMBZ5251B is rated for a maximum power dissipation of 350 mW at 25°C ambient, with derating above that temperature per its thermal resistance profile. This limit applies to continuous DC operation and assumes proper PCB copper area for heat spreading. The MMBZ5251B must not exceed this rating in sustained regulation or clamping duty cycles to avoid junction temperature exceeding +150°C.

Does MMBZ5251B have a specified forward voltage?

Yes, the MMBZ5251B specifies a maximum forward voltage of 0.9 V at 10 mA forward current. This value is consistent across the entire MMBZ5200 series and is critical for bidirectional transient suppression applications. When used in forward conduction-such as during negative ESD events-the MMBZ5251B clamps reliably below 0.9 V, ensuring protection of downstream circuitry without excessive voltage overshoot.

What is the reverse leakage current of MMBZ5251B at rated voltage?

The MMBZ5251B exhibits a maximum reverse leakage current of 0.1 µA at 17.6 V (0.8 × V_Z). This low leakage supports energy-efficient operation in always-on circuits like sensor bias rails and real-time clock backup supplies. The MMBZ5251B achieves this performance through controlled doping and passivation processes unique to Fairchild's planar Zener process, distinguishing it from higher-leakage alternatives.

Is MMBZ5251B compatible with standard SOT-23 pick-and-place equipment?

Yes, the MMBZ5251B uses a standard SOT-23 package with 0.95 mm pitch and JEDEC-compliant dimensions, fully supporting automated assembly using industry-standard nozzles and feeders. Its terminal configuration-Anode (Pin 1), Cathode (Pin 2), NC (Pin 3)-matches common SOT-23 placement libraries. The MMBZ5251B has been qualified for reflow profiles up to 260°C peak, ensuring robust solder joint formation without parametric shift.