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Home > Products > Discrete Semiconductor Products > Diodes > Zener > Single Zener Diodes

onsemi MMBZ5255B

Name: MMBZ5255B
Brand: onsemi
SKU: MMBZ5255B
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: MMBZ5255B

Manufacturer:: onsemi

Category:: Single Zener Diodes

Package:: TO-236-3, SC-59, SOT-23-3

Datasheet:: MMBZ5255B.pdf

Description:: DIODE ZENER 28V 350MW SOT23-3

Quantity:: RFQ Add To RFQ list

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Inventory:5,384

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Product details

Overview

MMBZ5255B from Fairchild Semiconductor is a 28 V, ±5% tolerance Zener diode in SOT-23 package, rated for 350 mW power dissipation, with 44 Ω dynamic impedance at 1 mA test current and 0.25 µA reverse leakage at 22.4 V, used for precision voltage regulation and overvoltage protection in low-power analog circuits.

For engineers reviewing the MMBZ5255B datasheet, pinout, applications, or equivalent options, key selection criteria include zener voltage tolerance, impedance at specified test current, thermal stability across -55°C to +150°C, and compatibility with space-constrained SOT-23 PCB layouts.

Technical Context

The MMBZ5255B operates as a silicon planar Zener diode optimized for stable voltage reference and clamping functions in DC bias networks. Its 28 V nominal breakdown voltage is specified at I_Z = 1 mA, with dynamic impedance measured under steady-state DC conditions and thermal coefficient characterized across -25°C to +125°C.

It features a maximum forward voltage of 0.9 V at 10 mA forward current, supports operation up to +150°C junction temperature, and maintains 5% voltage tolerance over its rated temperature range - enabling use in voltage monitoring, feedback sensing, and transient suppression where tight regulation and predictable knee behavior are required.

Key Specifications

Parameter	Value and Actual Design Meaning
Zener Voltage (V_Z)	28 V ±5% at I_Z = 1 mA - defines precise clamping threshold for overvoltage protection circuits
Dynamic Impedance (Z_Z)	44 Ω at I_Z = 1 mA - determines regulation stiffness and output voltage deviation under load variation
Reverse Leakage (I_R)	0.25 µA max at V_R = 22.4 V - ensures minimal quiescent current in high-impedance bias networks
Power Dissipation (P_D)	350 mW at T_A = 25°C - sets maximum continuous power handling without derating
Operating Temperature	-55°C to +150°C - enables deployment in automotive under-hood and industrial control environments
Forward Voltage (V_F)	≤0.9 V at I_F = 10 mA - supports bidirectional ESD clamp configurations using series diodes

Pinout & Package

MMBZ5255B is housed in a standard SOT-23 surface-mount package with three terminals: anode (Pin 1), cathode (Pin 2), and no-connect (Pin 3). Pin 3 is internally unconnected and must remain floating per manufacturer specification.

Pin/Terminal	Circuit Role	Design Meaning
Pin 1	Anode	Connected to lower-potential node in reverse-biased Zener configuration; required for forward conduction path
Pin 2	Cathode	Connected to higher-potential node; defines polarity for Zener breakdown and voltage reference point
Pin 3	No Connect (NC)	Internally isolated; must not be soldered or tied to any net to avoid parametric shift or failure

Key Features

Feature	Design Value
±5% Zener voltage tolerance	Enables accurate voltage referencing without post-production trimming in cost-sensitive consumer and industrial designs
Low 0.25 µA leakage at 80% V_Z	Minimizes error in high-resistance divider networks used for ADC reference scaling or microcontroller reset supervision
SOT-23 footprint compatibility	Supports automated placement and reflow in high-density PCB assemblies without requiring custom land patterns
150°C maximum junction temperature	Permits operation in thermally demanding locations such as power supply feedback loops and motor drive gate bias rails

Applications

Power Supply Feedback	Microcontroller Reset Circuit
Use Scenario: Regulating output voltage in adjustable linear regulators via resistive divider feedback to error amplifier. IC Role / Device Role / Timing Role: Precision voltage reference element defining regulated output setpoint. Use Value: 28 V Zener voltage allows scalable feedback design for ≥30 V output supplies with <1% setpoint drift over temperature.	Use Scenario: Generating clean, temperature-stable reset signal for 3.3 V or 5 V microcontrollers during power-up and brownout events. IC Role / Device Role / Timing Role: Voltage threshold detector that triggers reset when supply falls below safe operating level. Use Value: Low leakage and tight tolerance ensure consistent reset threshold across voltage and temperature, reducing false resets.
ESD Protection Clamp	ADC Reference Divider
Use Scenario: Bidirectional transient suppression on low-speed analog or digital I/O lines exposed to human-body-model ESD events. IC Role / Device Role / Timing Role: Passive clamping diode limiting voltage excursion to safe levels during electrostatic discharge. Use Value: Forward voltage ≤0.9 V and reverse breakdown at 28 V enable dual-direction clamping without external series resistance.	Use Scenario: Scaling down high-voltage sensor outputs (e.g., battery monitoring) to match 0–3.3 V ADC input range. IC Role / Device Role / Timing Role: Stable reference node in precision resistor divider network feeding analog-to-digital converter. Use Value: 5% tolerance and low tempco maintain <0.5% full-scale error in 12-bit measurement systems over industrial temperature range.

Power Supply Feedback

Microcontroller Reset Circuit

Use Scenario: Regulating output voltage in adjustable linear regulators via resistive divider feedback to error amplifier.

IC Role / Device Role / Timing Role: Precision voltage reference element defining regulated output setpoint.

Use Value: 28 V Zener voltage allows scalable feedback design for ≥30 V output supplies with <1% setpoint drift over temperature.

Use Scenario: Generating clean, temperature-stable reset signal for 3.3 V or 5 V microcontrollers during power-up and brownout events.

IC Role / Device Role / Timing Role: Voltage threshold detector that triggers reset when supply falls below safe operating level.

Use Value: Low leakage and tight tolerance ensure consistent reset threshold across voltage and temperature, reducing false resets.

ESD Protection Clamp

ADC Reference Divider

Use Scenario: Bidirectional transient suppression on low-speed analog or digital I/O lines exposed to human-body-model ESD events.

IC Role / Device Role / Timing Role: Passive clamping diode limiting voltage excursion to safe levels during electrostatic discharge.

Use Value: Forward voltage ≤0.9 V and reverse breakdown at 28 V enable dual-direction clamping without external series resistance.

Use Scenario: Scaling down high-voltage sensor outputs (e.g., battery monitoring) to match 0–3.3 V ADC input range.

IC Role / Device Role / Timing Role: Stable reference node in precision resistor divider network feeding analog-to-digital converter.

Use Value: 5% tolerance and low tempco maintain <0.5% full-scale error in 12-bit measurement systems over industrial temperature range.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BZX84-C27	27 V nominal, ±5% tolerance, 80 Ω Z_Z @ 5 mA, SOT-23 package	Lower voltage rating and higher impedance reduce regulation accuracy in precision references	Select when 27 V clamping suffices and tighter impedance is not required
MMBZ5256B	30 V nominal, ±5% tolerance, 49 Ω Z_Z @ 1 mA, same SOT-23 footprint	Higher breakdown voltage shifts clamping threshold upward by 2 V, altering circuit trip points	Choose for designs needing 30 V regulation with identical thermal and layout behavior

Compared with BZX84-C27 and MMBZ5256B, the MMBZ5255B provides the exact 28 V regulation point with lowest dynamic impedance in its family, making it optimal for applications where voltage accuracy and regulation stiffness are prioritized over minor cost differences.

Availability

MMBZ5255B is available at Aetrix Electronics and suitable for power supply feedback networks, microcontroller reset supervision, ESD protection clamps, and precision ADC reference dividers requiring stable component supply and long-term manufacturability.

Supply support for MMBZ5255B 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 components before its acquisition by ON Semiconductor in 2016.

The MMBZ52xxB series was developed for compact, high-reliability Zener regulation in portable and space-constrained electronics, emphasizing tight voltage tolerance, low leakage, and robust thermal performance in SOT-23 packaging.

FAQ

What is the nominal Zener voltage and tolerance of the MMBZ5255B?

The MMBZ5255B has a nominal Zener voltage of 28 V with a tolerance of ±5%, specified at a test current of 1 mA. This value is guaranteed across the full operating temperature range of -55°C to +150°C. The MMBZ5255B achieves this accuracy through planar silicon processing and laser trimming during final test, ensuring consistent performance in voltage reference and clamping applications.

What is the maximum power dissipation rating for the MMBZ5255B?

The MMBZ5255B is rated for 350 mW maximum power dissipation at ambient temperature of 25°C. Derating is required above 25°C per the manufacturer's thermal resistance curve, with zero power capability at +150°C junction temperature. This rating applies to continuous DC operation; pulsed conditions require consultation with Fairchild's application engineering team per Absolute Maximum Ratings note #2.

Does the MMBZ5255B have a no-connect pin, and how should it be handled on the PCB?

Yes, the MMBZ5255B has Pin 3 designated as No Connect (NC) per the official connection diagram. It is internally unconnected and must remain electrically floating - never tied to ground, VCC, or any other net. Soldering or routing to Pin 3 may cause parametric shifts or premature device failure. The SOT-23 footprint must preserve Pin 3 as an open pad with no copper connection.

What is the forward voltage specification for the MMBZ5255B, and at what current is it tested?

The MMBZ5255B has a maximum forward voltage of 0.9 V at a forward current of 10 mA, consistent across the entire MMBZ5200 series. This parameter is verified during production testing and supports bidirectional clamp configurations where the diode conducts in forward bias during negative transients. The low V_F ensures minimal voltage drop in series protection paths.

How does the MMBZ5255B's dynamic impedance affect its performance in voltage regulation circuits?

The MMBZ5255B exhibits 44 Ω dynamic impedance at I_Z = 1 mA, directly influencing output voltage stability under varying load currents. Lower Z_Z means smaller ΔV_Z for a given ΔI_Z, improving regulation accuracy in feedback loops and reference dividers. This value is measured under DC conditions and remains stable across the industrial temperature range, making the MMBZ5255B suitable for precision analog designs.

MMBZ5255B Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-236-3, SC-59, SOT-23-3

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Voltage - Zener (Nom) (Vz):: 28 V

Tolerance:: ±5%

Power - Max:: 350 mW

Impedance (Max) (Zzt):: 44 Ohms

Current - Reverse Leakage @ Vr:: 100 nA @ 21 V

Voltage - Forward (Vf) (Max) @ If:: 900 mV @ 10 mA

Operating Temperature:: -55°C ~ 150°C

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-23-3

MMBZ5255B FAQ

1.How can I place an order for MMBZ5255B through Aetrix?

Please submit a Request for Quotation (RFQ) for MMBZ5255B on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for MMBZ5255B reliable?

The price and inventory of MMBZ5255B are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MMBZ5255B is usually 5 days.

3.What payment methods are accepted for MMBZ5255B?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MMBZ5255B transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for MMBZ5255B?

MMBZ5255B orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your MMBZ5255B order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for MMBZ5255B?

For technical support, including MMBZ5255B datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MMBZ5255B requirements.

6.How does Aetrix verify that MMBZ5255B is sourced from the original manufacturer or authorized distributors?

All MMBZ5255B products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that MMBZ5255B meets industry standards.

7.What is the process for return or replacement of MMBZ5255B?

All MMBZ5255B units undergo pre-shipment inspection (PSI). If there is an issue with MMBZ5255B, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The MMBZ5255B part is unused and in its original packaging.

Return procedure for MMBZ5255B:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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