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Taiwan Semiconductor Corporation SMF78A
- Part No.:
- SMF78A
- Manufacturer:
- Taiwan Semiconductor Corporation
- Category:
- TVS Diodes
- Package:
- SOD-123W
- Datasheet:
-
SMF78A.pdf
- Description:
- TVS DIODE 78VWM 126VC SOD123W
- Quantity:
- Payment:
- Shipping:
Inventory:7,491
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Product details
Overview
SMF78A from Taiwan Semiconductor is a unidirectional surface-mount transient voltage suppressor (TVS) diode designed for high-energy surge protection in DC power lines and signal paths. It features a 78 V working stand-off voltage (VWM), 86.7–95.8 V breakdown voltage (VBR), 126 V clamping voltage (VC) at 1.4 A peak pulse current, and 200 W peak pulse power (10/1000 µs). It is used in automotive infotainment power rails to protect downstream LDOs and microcontrollers from load-dump transients.
For engineers reviewing the SMF78A datasheet, SMF78A pinout, SMF78A application, or SMF78A equivalent, key selection criteria include clamping performance under ISO 7637-2 Pulse 5a, thermal resistance (RθJL = 33 °C/W), SOD-123W package compatibility with automated assembly, and leakage current <1 µA at 78 V.
Technical Context
The SMF78A operates as a unidirectional avalanche diode, conducting only in reverse bias above its breakdown threshold to clamp transient overvoltages. Its glass-passivated junction ensures stable VBR tolerance and low leakage (<1 µA at VWM), while its SOD-123W package enables efficient heat dissipation via PCB copper pads (RθJA = 100 °C/W).
It meets ISO 7637-2 Pulse 1, 2a, 2b, 3a, and 3b immunity requirements and supports automotive-grade reliability with operating junction temperature from –55 °C to +175 °C, JESD201 Class 2 whisker resistance, and moisture sensitivity level 1.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VWM | 78 V - Maximum continuous reverse voltage before clamping begins; sets operating margin above nominal 60 V automotive supply. |
| VBR min/max | 86.7 V / 95.8 V - Breakdown occurs within this range at 1 mA test current; defines turn-on consistency across production lot. |
| VC @ IPPM | 126 V - Clamped voltage at 1.4 A peak pulse (10/1000 µs); determines maximum stress on protected IC inputs. |
| PPPM | 200 W - Peak pulse power handling capability; validates compliance with ISO 7637-2 Pulse 5a (load dump) waveform. |
| IR @ VWM | <1 µA - Reverse leakage at rated stand-off voltage; ensures negligible standby power loss in always-on circuits. |
| TJ max | +175 °C - Maximum junction temperature; enables use in under-hood environments with minimal derating. |
| RθJL | 33 °C/W - Junction-to-lead thermal resistance; supports reliable power dissipation when soldered to 5 mm × 5 mm Cu pad. |
Pinout & Package
Package: SOD-123W - Surface-mount plastic package with matte tin-plated leads, UL 94V-0 molding compound, cathode band polarity marking, and 0.016 g mass. Optimized for high-speed pick-and-place placement and reflow soldering per J-STD-002.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Anode | Forward conduction terminal | Connected to lower-potential side (e.g., ground or return path) in unidirectional configuration. |
| Cathode | Reverse-biased clamping terminal | Connected to protected line (e.g., 12 V rail); conducts during overvoltage to shunt energy to ground. |
Key Features
| Feature | Design Value |
|---|---|
| Glass-passivated junction | Ensures tight VBR tolerance (±5%) and long-term stability under thermal cycling and humidity exposure. |
| ISO 7637-2 compliance | Validated for Pulse 1 (inductive switch-off), Pulse 2a/2b (battery disconnect), and Pulse 3a/3b (line transients) - critical for automotive ECU design. |
| Low IR <1 µA @ VWM | Minimizes quiescent current draw in battery-backed systems such as telematics modules and ADAS sensors. |
| SOD-123W mechanical robustness | Meets JESD201 Class 2 whisker resistance and supports 260 °C reflow profile without delamination or lead fracture. |
Applications
| Automotive Power Rail Protection | Industrial Sensor Interface Protection |
|---|---|
Use Scenario: Protecting 12 V/24 V power input of body control modules against load-dump transients up to 120 V. IC Role / Device Role / Timing Role: Unidirectional TVS diode placed between power rail and ground, clamping surges within 1 ns response time. Use Value: Limits voltage seen by downstream DC-DC converters to ≤126 V, preventing latch-up or gate oxide damage in PMICs. | Use Scenario: Shielding RS-485 transceiver I/O pins from ESD and EFT events in factory automation PLCs. IC Role / Device Role / Timing Role: Low-capacitance (typ. 120 pF @ 1 MHz) unidirectional clamp on differential bus lines. Use Value: Maintains signal integrity up to 10 Mbps while absorbing 8 kV contact ESD per IEC 61000-4-2. |
| LED Driver Overvoltage Clamp | Consumer USB Port Surge Suppression |
Use Scenario: Safeguarding constant-current LED driver ICs in automotive headlamps from alternator-induced spikes. IC Role / Device Role / Timing Role: Parallel-connected TVS on output stage, triggered only during >86.7 V transients. Use Value: Prevents catastrophic failure of external MOSFETs and internal op-amps without affecting normal 60 V forward operation. | Use Scenario: Adding secondary-level surge protection on VBUS line of USB-C ports in portable medical devices. IC Role / Device Role / Timing Role: Secondary clamp after primary fuse and common-mode choke, handling residual 10/1000 µs surges. Use Value: Enables pass-fail compliance with IEC 61000-4-5 Level 3 (1 kV line-earth) without increasing board area beyond SOD-123W footprint. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar transient suppression applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| Littelfuse SMAJ78A | Same VWM (78 V), identical SOD-123 package, but higher VC = 129 V and lower PPPM = 400 W (tested at 10/1000 µs). | Marginally higher clamping voltage may require revalidation of protected IC's absolute maximum ratings. | Preferred where higher peak power margin is needed and 3 V higher VC is acceptable. |
| ON Semiconductor SMCJ78A | Different package (DO-214AB/SMB), larger footprint, higher PPPM = 1500 W, VC = 127 V, and VBR = 86.7–95.8 V (same range as SMF78A). | Not suitable for space-constrained layouts requiring SOD-123W; better for high-energy industrial surge events. | Select only when PCB layout allows SMB package and system requires >200 W surge handling. |
Compared with SMAJ78A and SMCJ78A, the SMF78A offers optimal balance of compact SOD-123W footprint, automotive-grade thermal performance (RθJL = 33 °C/W), and precise clamping (126 V), making it ideal for dense, thermally constrained ECUs where layout real estate and thermal management are critical.
Availability
SMF78A is available at Aetrix Electronics and suitable for automotive electronics, industrial sensor interfaces, LED driver designs, and consumer USB power protection requiring stable component supply and full traceability.
Supply support for SMF78A 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 headquartered in Hsinchu, Taiwan, specializing in discrete power devices, TVS diodes, rectifiers, and MOSFETs for automotive, industrial, and computing markets.
The SMF78A belongs to TSC's SMF series of surface-mount TVS diodes engineered specifically for ISO 7637-2-compliant automotive power line protection, emphasizing low leakage, tight VBR tolerance, and robust thermal performance in miniature packages.
FAQ
What is the clamping voltage of the SMF78A at its rated peak pulse current?
The SMF78A has a maximum clamping voltage (VC) of 126 V when subjected to its specified peak pulse current of 1.4 A with a 10/1000 µs waveform. This value is measured per standard test conditions in the datasheet and defines the upper voltage limit imposed on protected circuitry during surge events. The SMF78A maintains this clamping performance across its qualified operating temperature range and is validated for ISO 7637-2 Pulse 5a compliance.
Does the SMF78A meet automotive transient immunity standards?
Yes, the SMF78A meets ISO 7637-2 requirements for Pulse 1 (inductive load switch-off), Pulse 2a/2b (battery disconnection), and Pulse 3a/3b (capacitive coupling transients). It is not rated for Pulse 5a (load dump) in the base datasheet, but its 200 W PPPM rating and 126 V clamping voltage align with typical Pulse 5a test profiles when used with appropriate series impedance. System-level validation per ISO 16750-2 is recommended for full automotive qualification of the SMF78A.
What is the maximum junction temperature rating for the SMF78A?
The SMF78A has a maximum junction temperature (TJ max) of +175 °C, enabling reliable operation in under-hood automotive environments and high-ambient industrial settings. This rating is supported by its SOD-123W package construction, glass-passivated junction, and thermal resistance values (RθJL = 33 °C/W, RθJA = 100 °C/W on 5 mm × 5 mm Cu pad). Derating curves in the SMF78A datasheet define safe power limits above 25 °C ambient.
Is the SMF78A unidirectional or bidirectional, and how is polarity identified?
The SMF78A is a unidirectional TVS diode, meaning it clamps only in reverse bias and conducts forward like a standard diode. Polarity is indicated by a cathode band on the SOD-123W package body - the banded end connects to the protected line (e.g., 12 V rail), while the anode connects to ground. This configuration ensures low leakage (<1 µA) during normal operation and fast avalanche response during overvoltage events.
What is the marking code for the SMF78A on the device body?
The SMF78A is marked with the code "2W078" on its SOD-123W package body. This marking appears adjacent to the cathode band and is laser-etched for readability post-reflow. The "2W" prefix denotes the SMF series and power class, while "078" specifies the 78 V working stand-off voltage. Date and factory codes follow per TSC's standard marking diagram in the SMF78A datasheet.
SMF78A Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Taiwan Semiconductor Corporation
- Package/Case:
- SOD-123W
- Series:
- SMF
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Type:
- Zener
- Unidirectional Channels:
- 1
- Bidirectional Channels:
- -
- Voltage - Reverse Standoff (Typ):
- 78V
- Voltage - Breakdown (Min):
- 86.7V
- Voltage - Clamping (Max) @ Ipp:
- 126V
- Current - Peak Pulse (10/1000µs):
- 1.4A
- Power - Peak Pulse:
- 200W
- Power Line Protection:
- No
- Applications:
- General Purpose
- Capacitance @ Frequency:
- -
- Operating Temperature:
- -55°C ~ 175°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- SOD-123W
SMF78A FAQ
1.How can I place an order for SMF78A through Aetrix?
Please submit a Request for Quotation (RFQ) for SMF78A 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 SMF78A reliable?
The price and inventory of SMF78A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SMF78A is usually 5 days.
3.What payment methods are accepted for SMF78A?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SMF78A transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SMF78A?
SMF78A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SMF78A 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 SMF78A?
For technical support, including SMF78A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SMF78A requirements.
6.How does Aetrix verify that SMF78A is sourced from the original manufacturer or authorized distributors?
All SMF78A 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 SMF78A meets industry standards.
7.What is the process for return or replacement of SMF78A?
All SMF78A units undergo pre-shipment inspection (PSI). If there is an issue with SMF78A, 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 SMF78A part is unused and in its original packaging.
Return procedure for SMF78A:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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