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Taiwan Semiconductor Corporation SMAJ18
- Part No.:
- SMAJ18
- Manufacturer:
- Taiwan Semiconductor Corporation
- Category:
- TVS Diodes
- Package:
- DO-214AC, SMA
- Datasheet:
-
SMAJ18.pdf
- Description:
- 400W, 22.2V, 10%, UNIDIRECTIONAL
- Quantity:
- Payment:
- Shipping:
Inventory:8,398
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Product details
Overview
SMAJ18 from Taiwan Semiconductor is a unidirectional surface-mount transient voltage suppressor (TVS) diode in DO-214AC (SMA) package, designed for clamping fast transients in DC power lines. It features a 18 V working stand-off voltage (VWM), 20.0–24.4 V breakdown voltage (VBR), 32.2 V maximum clamping voltage (VC) at 12.4 A peak pulse current, and 400 W peak pulse power rating with 10/1000 µs waveform - used in SMPS input protection and DC/DC converter rail stabilization.
For engineers reviewing the SMAJ18 datasheet, SMAJ18 pinout, SMAJ18 application, or SMAJ18 equivalent, key selection criteria include clamping voltage margin relative to protected IC VDD, leakage current below 1 µA at 18 V, compliance with ISO 7637-2 Pulse 1/2a/2b/3a/3b, and compatibility with automated SMT placement on high-volume power supply PCBs.
Technical Context
The SMAJ18 operates as a unidirectional avalanche diode, triggered when reverse voltage exceeds its specified breakdown range (20.0–24.4 V at 1 mA test current). Its glass-passivated junction ensures stable VBR tolerance and low leakage (<1 µA at VWM = 18 V), while sub-1 ps response time enables effective suppression of ESD and load-dump transients before downstream components are stressed.
Thermal design relies on its 150 °C maximum junction temperature and 1 W steady-state power dissipation. Derating begins above 25 °C ambient per Fig.2, and peak pulse capability is defined for non-repetitive 10/1000 µs waveforms - not rated for repetitive surge conditions without thermal analysis.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VWM | 18 V - Maximum continuous reverse operating voltage before significant leakage; sets upper limit for protected line nominal voltage. |
| VBR min/max | 20.0 / 24.4 V at 1 mA - Confirmed avalanche onset range; ensures reliable turn-on above system overvoltage threshold. |
| VC @ IPPM | 32.2 V at 12.4 A - Clamped voltage during 10/1000 µs surge; defines worst-case stress on downstream ICs. |
| PPPM | 400 W - Peak pulse power handling with 10/1000 µs waveform; supports automotive load-dump and industrial surge immunity. |
| IR @ VWM | <1 µA - Reverse leakage at 18 V; negligible power loss and no measurable impact on standby current in battery-powered systems. |
| TJ max | 150 °C - Maximum junction temperature; enables operation in enclosed power enclosures with limited airflow. |
Pinout & Package
DO-214AC (SMA) surface-mount package: molded epoxy case with matte tin-plated leads, polarity indicated by cathode band, moisture sensitivity level 1 (J-STD-020), UL 94V-0 flammability rating, and 0.060 g typical weight.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Anode | Low-side reference terminal | Connected to ground or low-voltage return path; forms clamping path during transient events. |
| Cathode | High-side transient input terminal | Connected to protected line (e.g., +12 V rail); avalanche conduction occurs when voltage exceeds VBR relative to anode. |
Key Features
| Feature | Design Value |
|---|---|
| Glass-passivated junction | Ensures stable VBR tolerance and long-term reliability under thermal cycling and humidity exposure. |
| Fast response time <1 ps | Clamps transients before propagation into sensitive logic or analog circuitry - critical for protecting USB, CAN, or MCU I/O rails. |
| ISO 7637-2 compliance | Validated for automotive electrical disturbance immunity including Pulse 1 (inductive switch-off), Pulse 2a/2b (battery disconnect), and Pulse 3a/3b (capacitive coupling). |
| Automated placement compatibility | DO-214AC footprint and lead geometry support high-speed pick-and-place with standard vision alignment and reflow profiles. |
Applications
| Switching Mode Power Supply (SMPS) | On-board DC/DC Converter |
|---|---|
Use Scenario: Input stage protection against line surges and inductive kickback in AC/DC adapters and isolated flyback converters. IC Role / Device Role / Timing Role: Unidirectional TVS clamping element placed between rectified input and primary-side controller. Use Value: Limits transient voltage to ≤32.2 V during 400 W 10/1000 µs pulses, preventing damage to MOSFET gate oxide and controller UVLO circuitry. | Use Scenario: Output rail stabilization in point-of-load (POL) converters powering FPGAs or DSPs in telecom infrastructure. IC Role / Device Role / Timing Role: Secondary-side transient suppressor connected across regulated 3.3 V or 5 V output bus. Use Value: Maintains <1 µA leakage at 18 V stand-off, avoiding interference with tight output regulation and enabling accurate remote sensing. |
| Lighting Application | Automotive Body Control Module (BCM) |
Use Scenario: Protection of LED driver ICs and current-sense resistors in streetlight and commercial LED fixtures exposed to lightning-induced surges. IC Role / Device Role / Timing Role: Parallel-connected TVS on constant-current output path upstream of LED string. Use Value: Withstands 12.4 A peak impulse current without degradation, preserving luminance stability after repeated surge events. | Use Scenario: CAN bus power rail protection and microcontroller I/O line conditioning in BCMs subjected to ISO 7637-2 Pulse 1 and Pulse 2b. IC Role / Device Role / Timing Role: Unidirectional clamping device on 12 V supply input to BCM main PCB. Use Value: Meets full ISO 7637-2 test requirements, ensuring functional safety compliance without external filtering or redundancy. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar transient voltage suppression applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SMAJ18A | Narrower VBR range (20.0–22.1 V), lower clamping voltage (29.2 V), same package and VWM. | Better suited for tighter clamping margins where protected IC absolute maximum rating is ≤30 V. | Select SMAJ18A when VC margin is critical and system VDD tolerances are narrow; SMAJ18 offers higher surge robustness at slightly elevated clamping. |
| SMCJ18 | Same VWM and VBR range but in larger DO-214AB (SMC) package; 1500 W peak power rating. | Used where higher energy absorption is required (e.g., front-end automotive battery inputs), not drop-in compatible due to footprint mismatch. | Choose SMCJ18 only if board layout allows larger SMC footprint and system requires >400 W pulse handling - not a direct replacement. |
Compared with SMAJ18A and SMCJ18, the SMAJ18 balances moderate clamping voltage (32.2 V), industry-standard DO-214AC footprint, and 400 W surge capacity - making it optimal for space-constrained, cost-sensitive DC power rail protection where ISO 7637-2 compliance and automated assembly are mandatory.
Availability
SMAJ18 is available at Aetrix Electronics and suitable for switching mode power supplies, on-board DC/DC converters, and lighting applications requiring stable component supply, consistent parametric performance, and RoHS-compliant manufacturing.
Supply support for SMAJ18 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
Taiwan Semiconductor Corporation (TSC) is a vertically integrated semiconductor manufacturer specializing in discrete power devices, TVS diodes, rectifiers, and MOSFETs for industrial, computing, and automotive markets.
The SMAJ series was developed specifically for surface-mount transient suppression in high-volume power conversion systems, emphasizing automated assembly compatibility, ISO 7637-2 compliance, and stable parametric consistency across production lots.
FAQ
What is the maximum clamping voltage of the SMAJ18 under standard test conditions?
The SMAJ18 has a maximum clamping voltage (VC) of 32.2 V when subjected to its rated peak pulse current of 12.4 A using the 10/1000 µs waveform. This value is measured at the device terminals and represents the worst-case voltage seen by downstream components during surge events - critical for verifying margin against IC absolute maximum ratings.
Is the SMAJ18 suitable for bidirectional transient suppression?
No, the SMAJ18 is a unidirectional TVS diode intended for DC line protection with defined polarity. For bidirectional applications such as AC signal lines or differential buses, the SMAJ18C or SMAJ18CA variants must be used - these include internal back-to-back diode configuration and are explicitly marked with "C" or "CA" suffixes.
Does the SMAJ18 meet automotive electromagnetic compatibility standards?
Yes, the SMAJ18 meets ISO 7637-2 requirements for electrical disturbances in road vehicles, including Pulse 1 (inductive load dump), Pulse 2a/2b (battery disconnection), and Pulse 3a/3b (capacitive coupling). This makes it suitable for use in automotive body control modules, infotainment power supplies, and lighting ECUs.
What is the reverse leakage current specification for the SMAJ18 at its working voltage?
The SMAJ18 exhibits a maximum reverse leakage current (IR) of 1 µA when biased at its working stand-off voltage (VWM) of 18 V. This ultra-low leakage ensures minimal impact on system standby power consumption and avoids false triggering in high-impedance monitoring circuits.
Can the SMAJ18 be used in place of the SMAJ18A in an existing design?
The SMAJ18 and SMAJ18A share identical VWM (18 V) and DO-214AC package, but differ in VBR (20.0–24.4 V vs. 20.0–22.1 V) and clamping voltage (32.2 V vs. 29.2 V). Substitution is possible only if the downstream circuit can tolerate the 3.0 V higher VC - verify margin against IC absolute maximum ratings before replacement.
SMAJ18 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Taiwan Semiconductor Corporation
- Package/Case:
- DO-214AC, SMA
- Series:
- SMAJ
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Type:
- Zener
- Unidirectional Channels:
- 1
- Bidirectional Channels:
- -
- Voltage - Reverse Standoff (Typ):
- 18V
- Voltage - Breakdown (Min):
- 20V
- Voltage - Clamping (Max) @ Ipp:
- 32.2V
- Current - Peak Pulse (10/1000µs):
- 12.4A
- Power - Peak Pulse:
- 400W
- Power Line Protection:
- No
- Applications:
- General Purpose
- Capacitance @ Frequency:
- -
- Operating Temperature:
- -55°C ~ 150°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- DO-214AC (SMA)
SMAJ18 FAQ
1.How can I place an order for SMAJ18 through Aetrix?
Please submit a Request for Quotation (RFQ) for SMAJ18 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 SMAJ18 reliable?
The price and inventory of SMAJ18 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SMAJ18 is usually 5 days.
3.What payment methods are accepted for SMAJ18?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SMAJ18 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SMAJ18?
SMAJ18 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SMAJ18 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 SMAJ18?
For technical support, including SMAJ18 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SMAJ18 requirements.
6.How does Aetrix verify that SMAJ18 is sourced from the original manufacturer or authorized distributors?
All SMAJ18 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 SMAJ18 meets industry standards.
7.What is the process for return or replacement of SMAJ18?
All SMAJ18 units undergo pre-shipment inspection (PSI). If there is an issue with SMAJ18, 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 SMAJ18 part is unused and in its original packaging.
Return procedure for SMAJ18:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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