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HomeProductsCircuit ProtectionTVS - DiodesSMAJ78H
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SMAJ78H - Taiwan Semiconductor Corporation

Manufacturer Part Number
SMAJ78H
Manufacturer
Taiwan Semiconductor
Allelco Part Number
98D-SMAJ78H
Warranty
1 Year Allelco Warranty - Find out more
Stock Status:
32,564 pcs available, New & Original
Parts Description
TVS DIODE 78VWM 139VC DO214AC
Package
DO-214AC (SMA)
Data sheet
SMAJ78H.pdf
RoHs Status
ROHS3 Compliant
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Our certification
In stock: 32564
  • Unit Price: $0.099
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Specifications

SMAJ78H Tech Specifications
Taiwan Semiconductor Corporation - SMAJ78H technical specifications, attributes, parameters and parts with similar specifications to Taiwan Semiconductor Corporation - SMAJ78H

Product Attribute Attribute Value
Manufacturer Taiwan Semiconductor
Voltage - Reverse Standoff (Typ) 78V
Voltage - Clamping (Max) @ Ipp 139V
Voltage - Breakdown (Min) 86.7V
Unidirectional Channels 1
Type Zener
Supplier Device Package DO-214AC (SMA)
Series Automotive, AEC-Q101, SMAJ
Power Line Protection No
Product Attribute Attribute Value
Power - Peak Pulse 400W
Package / Case DO-214AC, SMA
Package Tape & Reel (TR)
Operating Temperature -55°C ~ 150°C (TJ)
Mounting Type Surface Mount
Current - Peak Pulse (10/1000µs) 2.9A
Capacitance @ Frequency -
Base Product Number SMAJ78
Applications Automotive

Environmental & Export Classifications

ATTRIBUTE DESCRIPTION
RoHs Status ROHS3 Compliant
Moisture Sensitivity Level (MSL) 1 (Unlimited)
REACH Status REACH Unaffected
ECCN EAR99
HTSUS 8541.10.0080

Frequently Asked Questions(FAQ)

How does the SMAJ78H’s peak pulse power rating of 400W compare to other diodes in the SMAJ series when protecting automotive ECUs from voltage transients?
The SMAJ78H delivers a peak pulse power dissipation of 400W, which is typical across most members of the SMAJ series. This level of energy handling makes it suitable for protecting sensitive automotive electronic control units (ECUs) against transient events such as load dump or electrostatic discharge. While higher-voltage variants like the SMAJ150H maintain similar power ratings, lower-voltage devices such as the SMAJ3.3A may be preferred for low-energy protection scenarios due to their smaller footprint and lower clamping characteristics. The consistent 400W capability across the series allows designers to scale protection levels without changing the fundamental overstress mitigation strategy.
What is the significance of the SMAJ78H’s reverse standoff voltage being specified at 78V, and how does this influence system-level protection architecture?
The 78V reverse standoff voltage means the SMAJ78H remains inactive under normal operating conditions where input voltages remain below this threshold. This ensures minimal leakage current and preserves signal integrity in systems such as infotainment modules or sensor interfaces powered by 12V or 24V rails. In automotive applications, this precision enables targeted protection without disrupting regulated downstream circuitry. When combined with its 86.7V breakdown voltage, it provides a defined trigger point that activates only during overvoltage events, balancing sensitivity and robustness.
Can the SMAJ78H be used effectively in unidirectional surge suppression circuits, and what considerations apply when implementing it in high-reliability automotive environments?
Yes, the SMAJ78H is designed for unidirectional protection, making it ideal for clamping positive-going transients common in automotive bus systems like LIN, CAN, or power line surges. Its AEC-Q101 qualification confirms suitability for automotive-grade reliability, ensuring long-term stability under thermal cycling and vibration. Engineers should ensure adequate PCB layout practices—such as short lead lengths and proximity to the protected node—to minimize inductance and maximize transient response speed. Additionally, derating the continuous working voltage by 20–30% enhances margin against aging effects and manufacturing tolerances.
How does the clamping behavior of the SMAJ78H at 139V compare to alternative TVS diodes with lower clamping voltages but similar power ratings?
At 139V clamping, the SMAJ78H limits downstream voltage to approximately 1.78 times its standoff voltage under maximum pulse conditions. Alternatives like the SMBJ78CA offer a slightly tighter clamp (~125V), which can reduce stress on protected components but may require more precise system design to avoid nuisance triggering. The trade-off lies in response speed versus clamping aggressiveness; while SMBJ-series devices have faster response times, the SMAJ78H’s 400W rating supports longer-duration pulses common in automotive load dump scenarios exceeding 100µs. Selection depends on whether the system prioritizes fast action or sustained energy absorption.
Is the SMAJ78H compatible with automated pick-and-place assembly processes, and what packaging details must be verified before integration?
Yes, the SMAJ78H is packaged in tape and reel format conforming to standard JEDEC DO-214AC (SMA) dimensions, enabling compatibility with surface-mount technology (SMT) assembly lines. Key parameters include a 2.9mm lead pitch and 5.3mm overall length, aligning with industry-standard pick-up nozzles and feeder configurations. Designers should verify land pattern geometry on PCBs to match the component’s solder pad layout, typically requiring 0.8mm pads with 0.3mm spacing. MSL Level 1 classification indicates unlimited floor life, simplifying inventory management and reducing risk of moisture-related defects during reflow soldering.
What role does capacitance play in selecting the SMAJ78H for high-speed communication lines, and is there any limitation implied by its datasheet?
Although capacitance is not explicitly listed in the SMAJ78H’s key specifications, typical SMAJ-series diodes exhibit junction capacitances between 100–300pF, which can affect signal integrity on high-frequency lines such as Gigabit Ethernet or USB interfaces. For applications where capacitive loading must be minimized, engineers might consider ultra-low-capacitance alternatives like the P6KE series, though these often sacrifice peak pulse power. If the SMAJ78H is deployed in a 100BASE-TX network or CAN-FD system, its moderate capacitance may introduce negligible delay but could degrade rise/fall times if routed near tightly coupled traces. System simulation or empirical testing is recommended to validate performance.
How does the operating temperature range of -55°C to +150°C impact the long-term reliability of the SMAJ78H in under-hood automotive applications?
The extended operating temperature range covers nearly all expected environmental conditions in automotive environments, including cold starts at -40°C and prolonged exposure to engine bay heat exceeding 105°C. The upper limit of 150°C reflects junction temperature capability, requiring careful thermal management via proper copper pour areas and airflow considerations. Over time, repeated thermal cycling can cause metallization degradation, but AEC-Q101 qualification includes accelerated life tests simulating 1,000 cycles between -40°C and +125°C. As long as the device is not exposed beyond its absolute maximum ratings, the SMAJ78H maintains stable electrical parameters throughout its projected lifespan.
Why might an engineer choose the SMAJ78H over discrete Zener-based protection circuits despite both offering similar voltage thresholds?
The SMAJ78H integrates avalanche multiplication and precise Zener-like regulation into a single monolithic structure optimized for transient suppression, whereas discrete Zeners often suffer from poor regulation under high-current pulses due to parasitic inductance and slower response. With a 2.9A peak current rating, the SMAJ78H handles load dump transients more effectively than parallel Zener-resistor networks, which dissipate energy inefficiently. Furthermore, its compact DO-214AC footprint reduces board space and simplifies BOM complexity, lowering assembly costs and improving yield in mass-produced vehicles.
What are the implications of the RoHS3 compliance status for sourcing and regulatory adherence when using the SMAJ78H in global automotive supply chains?
RoHS3 compliance ensures the SMAJ78H meets EU Directive 2015/863 restrictions on four phthalates, expanding beyond the original six substances covered by RoHS2. This broadens its acceptability in European markets and aligns with OEM requirements such as those from Volkswagen, BMW, or Renault. Combined with REACH unaffected status and EAR99 export classification, the device presents minimal regulatory hurdles across North America, Europe, and Asia. Suppliers must still confirm full compliance documentation, as some regions impose additional local restrictions unrelated to standard RoHS criteria.
How does the base product number SMAJ78 relate to the specific variant SMAJ78H, and what functional differences justify the “H” suffix?
The base number SMAJ78 denotes a family of transient voltage suppressors sharing core electrical characteristics such as 78V standoff and 139V clamping. The “H” suffix typically indicates enhanced performance attributes, such as improved surge withstand capability or tighter breakdown tolerance compared to non-H versions like the SMAJ78A. While exact distinctions vary by manufacturer, Taiwan Semiconductor Corporation uses “H” to denote higher ruggedness, possibly through optimized doping profiles or epitaxial layer design. Always consult the latest datasheet, as suffix interpretations are not universal across vendors.
In a dual-supply system requiring bidirectional protection, would two SMAJ78H diodes be an appropriate solution, and what configuration would be recommended?
Deploying two SMAJ78H diodes in back-to-back orientation—one unidirectional forward-biased and one reverse-biased—can provide bidirectional clamping, commonly referred to as a bi-directional TVS array. However, this approach doubles parasitic capacitance and increases package size relative to dedicated bi-directional devices like the SMAJ78CA (which integrates two channels). For symmetric protection on balanced lines such as differential CAN transceivers, a true bi-directional component offers superior symmetry and lower crosstalk. If space or cost constraints favor discrete parts, matching both SMAJ78H units carefully and placing them close to connectors minimizes imbalance.
What precautions should be taken when integrating the SMAJ78H into a 24V industrial control system prone to inductive kickback?
Inductive loads such as relays or solenoids generate reverse EMFs that can exceed 100V even in non-automotive settings. The SMAJ78H’s 78V standoff voltage provides sufficient headroom for nominal 24V systems, but transient spikes may approach or exceed 86.7V breakdown. To ensure reliable operation, add series resistance or use snubber circuits to limit di/dt, thereby reducing peak current demand on the diode. Also, position the SMAJ78H as close as possible to the load terminals to minimize loop inductance and maximize transient energy absorption efficiency.
Does the absence of Power Line Protection designation imply limitations when using the SMAJ78H in AC mains applications?
Correct. The lack of "Power Line Protection" labeling indicates the SMAJ78H is not rated for direct connection to AC mains or high-energy grid disturbances such as lightning-induced surges. Such applications require specialized components with reinforced isolation, higher energy ratings (e.g., 600W+), and compliance with safety standards like IEC 61000-4-5. Using the SMAJ78H in AC line protection risks catastrophic failure, as its 400W rating and 2.9A pulse current are insufficient for typical power line transients lasting hundreds of milliseconds. It remains appropriate only for low-voltage DC or signal-line protection.
How does the moisture sensitivity level (MSL) rating of 1 benefit procurement and production scheduling when managing inventory of SMAJ78H components?
MSL Level 1 signifies that the SMAJ78H requires no special handling or baking prior to reflow soldering, allowing it to be stored indefinitely under normal ambient conditions without degradation. This simplifies Just-in-Time inventory strategies and reduces warehousing costs, particularly beneficial in high-volume automotive manufacturing where supply chain disruptions are common. Unlike MSL 2 or 3 devices, there is no requirement to track storage duration or implement humidity monitoring, streamlining logistics and minimizing risk of popcorn cracking during thermal cycling.
Given its automotive grade and AEC-Q101 qualification, what testing protocols does the SMAJ78H undergo that differentiate it from commercial-grade TVS diodes?
AEC-Q101 certification mandates rigorous environmental and lifecycle stress testing, including high-temperature reverse bias (HTRB), highly accelerated stress test (HAST), thermal shock, and power cycling. These tests simulate decade-long operational exposure under harsh conditions, ensuring the SMAJ78H retains parametric stability far beyond commercial equivalents. Commercial-grade parts may pass basic continuity checks but fail under prolonged thermal or voltage stress, leading to early field failures. The SMAJ78H’s qualification provides traceable evidence of reliability required by Tier-1 suppliers serving major automakers.
Can the SMAJ78H be paralleled with another TVS diode to increase total surge current capacity, and what challenges arise from such an arrangement?
Paralleling multiple SMAJ78H diodes can theoretically increase current-handling capability, but requires precise current sharing due to inherent device mismatches in Vbr and dynamic impedance. Without active balancing, one diode may absorb disproportionate energy during a surge, leading to localized heating and potential burnout. Additionally, interconnect inductance between devices introduces impedance imbalances, undermining effectiveness. For critical applications, integrated arrays or higher-rated single devices are preferred. If parallel use is unavoidable, thermal coupling and identical part numbers minimize divergence, though derating each unit by 50% is strongly advised.
What impact does the DO-214AC (SMA) package size have on thermal performance and mounting options compared to larger packages like SOD-123FL?
The SMA package measures approximately 5.3 × 2.9mm, offering a balance between compactness and heat dissipation capability. While not as thermally robust as larger cases like TO-220 or SOD-123FL, it provides adequate thermal conductivity for pulsed energy applications where duty cycles are low. Mounting directly onto copper planes with vias improves heat spreading, extending surge endurance. In contrast, SOD-123FL packages have lower thermal mass but similar electrical performance; however, they occupy less area and suit high-density designs. Choice depends on available PCB real estate versus required surge repetition frequency.
How should the SMAJ78H be evaluated during prototype validation to ensure it meets both transient suppression and long-term drift requirements?
During testing, apply standardized surge waveforms per IEC 61000-4-5 (1.2/50µs voltage and 8/20µs current) up to the rated 2.9A peak while monitoring clamping voltage on the protected circuit. Simultaneously perform accelerated aging tests at elevated temperatures (e.g., 125°C) for 1,000 hours to assess parameter drift in Vbr and Vc. Compare pre- and post-stress measurements to ensure less than ±5% variation. Additionally, conduct visual inspections after thermal cycling to detect delamination or solder joint fatigue. Successful validation confirms the SMAJ78H maintains protection integrity across expected operational extremes.

Parts with Similar Specifications

The three parts on the right have similar specifications to Taiwan Semiconductor Corporation SMAJ78H

Product Attribute SMAJ78CAHR3G SMAJ78CHR3G SMAJ78CH SMAJ78HR3G
Part Number SMAJ78CAHR3G SMAJ78CHR3G SMAJ78CH SMAJ78HR3G
Manufacturer Taiwan Semiconductor Corporation Taiwan Semiconductor Corporation Taiwan Semiconductor Corporation Taiwan Semiconductor Corporation
Voltage - Clamping (Max) @ Ipp - - - -
Current - Peak Pulse (10/1000µs) - - - -
Mounting Type - Surface Mount Through Hole Surface Mount
Capacitance @ Frequency - - - -
Unidirectional Channels - - - -
Series - - - -
Applications - - - -
Power - Peak Pulse - - - -
Base Product Number - DAC34H84 MAX500 ADS62P42
Supplier Device Package - 196-NFBGA (12x12) 16-PDIP 64-VQFN (9x9)
Operating Temperature - -40°C ~ 85°C 0°C ~ 70°C -40°C ~ 85°C
Voltage - Reverse Standoff (Typ) - - - -
Power Line Protection - - - -
Package - Tape & Reel (TR) Tube Tape & Reel (TR)
Voltage - Breakdown (Min) - - - -
Type - - - -
Package / Case - 196-LFBGA 16-DIP (0.300', 7.62mm) 64-VFQFN Exposed Pad

SMAJ78H Datasheet PDF

Download SMAJ78H pdf datasheets and Taiwan Semiconductor Corporation documentation for SMAJ78H - Taiwan Semiconductor Corporation.

PCN Part Number
Part Number Update 1/Jan/2021.pdf

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SMAJ78H Image

SMAJ78H

Taiwan Semiconductor Corporation
98D-SMAJ78H

Want a better price? Add to Cart and Submit RFQ now, we'll contact you immediately.

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