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onsemi SA18A
- Part No.:
- SA18A
- Manufacturer:
- onsemi
- Category:
- TVS Diodes
- Package:
- DO-204AC, DO-15, Axial
- Datasheet:
-
SA18A.pdf
- Description:
- TVS DIODE 18VWM 29.2VC DO15
- Quantity:
- Payment:
- Shipping:
Inventory:4,830
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Product details
Overview
SA18A from Fairchild Semiconductor is a unidirectional 500 W transient voltage suppressor (TVS) diode designed for primary-level overvoltage protection in DC power lines and signal interfaces. It features a 18 V reverse stand-off voltage (VRWM), 20.0–22.1 V breakdown voltage (VBR) at 1.0 mA, 29.2 V clamping voltage (VC) at 17.2 A peak pulse current (IPPM), and operates up to +175 °C junction temperature.
For engineers reviewing the SA18A datasheet, pinout, applications, or equivalent options, this device is selected for robust surge immunity in industrial power supplies, automotive body electronics, and telecom interface protection where fast clamping (<1.0 ps response), low leakage (<1 µA above 10 V), and DO-15 package compatibility are critical.
Technical Context
The SA18A employs a glass-passivated PN junction optimized for high-energy transient suppression on the standardized 10/1000 µs waveform. Its unidirectional configuration provides asymmetric conduction-low forward voltage drop during normal operation and rapid avalanche breakdown under reverse overvoltage events.
It delivers 500 W peak pulse power (PPPM) with low incremental surge resistance and excellent clamping ratio (VC/VBR ≈ 1.46), enabling effective voltage limiting without excessive thermal stress. The device is rated for non-repetitive surge currents up to 70 A (IFSM) and supports stable operation across -65 °C to +175 °C storage and junction temperature ranges.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Peak Pulse Power (10/1000 µs) | 500 W - sustains single high-energy surges per IEC 61000-4-5 Level 4 without failure |
| Reverse Stand-off Voltage (VRWM) | 18 V - maximum continuous DC operating voltage before significant leakage begins |
| Breakdown Voltage (VBR) | 20.0–22.1 V at 1.0 mA - precise avalanche onset threshold for reliable triggering |
| Clamping Voltage (VC) | 29.2 V at 17.2 A IPPM - limits downstream circuit voltage during surge, protecting ICs and sensors |
| Peak Pulse Current (IPPM) | 17.2 A - maximum transient current the device safely shunts at rated clamping voltage |
| Reverse Leakage (IR) | <1 µA at VRWM - negligible standby power loss and minimal interference in high-impedance circuits |
| Junction Temperature (TJ) | +175 °C - enables use in under-hood automotive or enclosed industrial environments |
Pinout & Package
SA18A is housed in a standard DO-15 axial leaded package with cathode indicated by a color band. The device has two terminals: anode and cathode. No internal connections beyond the PN junction; polarity must be observed for correct unidirectional clamping.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Anode | Forward conduction terminal | Connected to ground or lower-potential rail; completes path during surge clamping |
| Cathode | Avalanche breakdown terminal | Connected to protected line; blocks normal voltage, avalanches during overvoltage |
Key Features
| Feature | Design Value |
|---|---|
| Glass-passivated junction | Enhances long-term reliability and moisture resistance in harsh environments (e.g., automotive under-hood) |
| Fast response time | <1.0 ps from 0 V to BV - ensures clamping initiates before sensitive downstream components experience overvoltage |
| Low incremental surge resistance | Minimizes VC rise under high IPPM - improves clamping accuracy and reduces energy dissipation in the TVS |
| 500 W peak pulse rating | Meets IEC 61000-4-5 surge immunity requirements for industrial and automotive applications |
| DO-15 mechanical compatibility | Enables drop-in replacement in legacy designs using industry-standard axial-leaded TVS footprints |
Applications
| Industrial Power Supply Protection | Automotive Body Control Module (BCM) |
|---|---|
Use Scenario: 24 V DC input stage of programmable logic controller (PLC) power supply exposed to load dump and inductive switching transients. IC Role / Device Role: Primary overvoltage clamp placed between input rail and ground to limit surge voltage to safe levels for upstream rectifier and downstream regulator ICs. Use Value: Clamps 17.2 A transients to ≤29.2 V, preventing damage to 36 V-rated input capacitors and 30 V-input DC/DC controllers. |
Use Scenario: LIN bus line protection in door module ECU subjected to ISO 7637-2 Pulse 1, 2a, and 5a transients. IC Role / Device Role: Unidirectional TVS on LIN data line referenced to vehicle chassis ground. Use Value: Blocks negative transients while allowing normal LIN signaling; <1 µA leakage avoids bus pull-up interference at 12 V nominal. |
| Telecom Interface Surge Protection | DC Motor Driver Input Stage |
Use Scenario: RS-485 transceiver power rail (VCC) in outdoor base station equipment subject to lightning-induced surges. IC Role / Device Role: Secondary protection device after gas discharge tube (GDT), providing fast, low-clamp final-stage suppression. Use Value: 29.2 V clamping ensures VCC stays below absolute maximum rating of RS-485 transceivers (typically 36 V), even during 500 W surges. |
Use Scenario: H-bridge driver power input in automated gate controller experiencing back-EMF spikes during motor commutation. IC Role / Device Role: Unidirectional TVS across DC bus to absorb inductive kickback energy. Use Value: 500 W rating handles repetitive 10/1000 µs spikes from 24 V, 5 A motors; DO-15 form factor allows direct PCB mounting near motor terminals. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar transient voltage suppression applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SMBJ18A (ON Semiconductor) | Same VRWM (18 V), but SMB package (surface-mount); 600 W PPPM; slightly higher VC (30.2 V @ 16.7 A) | Requires PCB rework for SMT layout; better suited for space-constrained, high-volume consumer designs | Select when board space is limited and automated assembly is required; verify thermal pad design for 600 W pulse handling |
| P6KE18A (Littelfuse) | Same DO-15 package and VRWM; 600 W PPPM; VC = 27.7 V @ 18.2 A; tighter VBR tolerance (20.0–21.5 V) | Higher surge margin and lower clamping; identical through-hole footprint enables direct replacement | Preferred for new designs requiring enhanced surge headroom or tighter VBR consistency; no layout change needed |
Compared with SA18A, SMBJ18A offers higher power and SMT compatibility at the cost of through-hole elimination, while P6KE18A delivers improved clamping and surge margin in the same DO-15 form factor-making it a drop-in upgrade for demanding industrial deployments.
Availability
SA18A is available at Aetrix Electronics and suitable for industrial power supplies, automotive body electronics, telecom interface protection, and DC motor drive systems requiring stable component supply, long-lifecycle support, and traceable sourcing.
Supply support for SA18A 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 leading designer and manufacturer of high-performance analog and power semiconductor solutions, acquired by ON Semiconductor in 2016; its legacy TVS portfolio remains widely deployed and supported.
The SAxxA series was developed specifically for robust, cost-effective transient suppression in DC-fed systems across automotive, industrial, and communications infrastructure-emphasizing reliability, standardized testing compliance, and broad voltage coverage.
FAQ
What is the clamping voltage of SA18A and how is it measured?
The SA18A has a maximum clamping voltage (VC) of 29.2 V, measured at 17.2 A peak pulse current (IPPM) under the standardized 10/1000 µs double-exponential surge waveform. This value reflects the actual voltage seen across the SA18A terminals during worst-case transient events and is critical for ensuring downstream components remain within their absolute maximum ratings. The test condition is defined in the Fairchild SA5V0(C)A–SA170(C)A datasheet Rev. D.
Is SA18A bidirectional or unidirectional?
SA18A is a unidirectional transient voltage suppressor, meaning it functions as a Zener-like clamp only in reverse bias and conducts freely in forward bias like a standard diode. Its part number lacks the "C" suffix (e.g., SA18CA), which denotes bidirectional variants. This makes SA18A appropriate for DC line protection where polarity is fixed and forward conduction is acceptable during fault conditions.
What package type does SA18A use and what are its mechanical dimensions?
SA18A uses the industry-standard DO-15 axial-leaded package, with a body diameter of approximately 2.5 mm and overall length of ~7.6 mm. Leads are tinned copper, spaced 5.0 mm apart, and the cathode is marked by a colored band. This package supports manual or wave-solder assembly and provides adequate thermal mass for 500 W pulse dissipation when mounted with 0.375" lead length per JEDEC standards.
Can SA18A replace SA18CA in a circuit?
No-SA18A cannot directly replace SA18CA because they differ fundamentally in functionality: SA18A is unidirectional and only clamps reverse overvoltages, while SA18CA is bidirectional and clamps surges of either polarity. Substituting SA18A for SA18CA in AC-coupled or floating signal lines would leave positive-going transients unprotected. Circuit topology and signal polarity must be verified before interchange.
What is the maximum junction temperature rating for SA18A and why does it matter?
The SA18A has a maximum operating junction temperature (TJ) of +175 °C, confirmed in the Absolute Maximum Ratings table of the Fairchild datasheet. This high rating allows reliable operation in thermally demanding environments such as engine compartments, enclosed industrial enclosures, or high-power LED drivers-where ambient temperatures may exceed 100 °C and self-heating from leakage or surge events must be accommodated without derating or failure.
SA18A Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Package/Case:
- DO-204AC, DO-15, Axial
- Series:
- -
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Type:
- Zener
- Unidirectional Channels:
- 1
- Bidirectional Channels:
- -
- Voltage - Reverse Standoff (Typ):
- 18V
- Voltage - Breakdown (Min):
- 20V
- Voltage - Clamping (Max) @ Ipp:
- 29.2V
- Current - Peak Pulse (10/1000µs):
- 17.2A
- Power - Peak Pulse:
- 500W
- Power Line Protection:
- No
- Applications:
- General Purpose
- Capacitance @ Frequency:
- -
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- DO-15
SA18A FAQ
1.How can I place an order for SA18A through Aetrix?
Please submit a Request for Quotation (RFQ) for SA18A 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 SA18A reliable?
The price and inventory of SA18A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SA18A is usually 5 days.
3.What payment methods are accepted for SA18A?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SA18A transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SA18A?
SA18A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SA18A 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 SA18A?
For technical support, including SA18A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SA18A requirements.
6.How does Aetrix verify that SA18A is sourced from the original manufacturer or authorized distributors?
All SA18A 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 SA18A meets industry standards.
7.What is the process for return or replacement of SA18A?
All SA18A units undergo pre-shipment inspection (PSI). If there is an issue with SA18A, 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 SA18A part is unused and in its original packaging.
Return procedure for SA18A:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SA18A Tags
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onsemi
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Diodes Incorporated
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Diodes Incorporated
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Diodes Incorporated
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onsemi
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Diodes Incorporated
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Diodes Incorporated
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Nexperia USA Inc.
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Toshiba Semiconductor and Storage
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Diodes Incorporated
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