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STMicroelectronics SM4T18AY
- Part No.:
- SM4T18AY
- Manufacturer:
- STMicroelectronics
- Category:
- TVS Diodes
- Package:
- DO-214AC, SMA
- Datasheet:
-
SM4T18AY.pdf
- Description:
- TVS DIODE 15VWM 32.5VC SMA
- Quantity:
- Payment:
- Shipping:
Inventory:2,685
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Product details
Overview
SM4T18AY from STMicroelectronics is an AEC-Q101-qualified unidirectional automotive TVS diode in SMA package, designed to clamp transient surges up to 32.5 A (8/20 µs) with a clamping voltage of 24.4 V and stand-off voltage of 15 V. It delivers 400 W peak pulse power (10/1000 µs), operates up to 150 °C junction temperature, and meets ISO 7637-2 Pulse 1/2a/3a/3b and ISO 10605 ESD immunity requirements for 12 V automotive power networks.
For engineers reviewing the SM4T18AY datasheet, SM4T18AY pinout, SM4T18AY application, or SM4T18AY equivalent, this device is selected for robust front-end protection of CAN transceivers, LIN bus nodes, and body control modules where low leakage (≤1 µA at 85 °C), high surge reliability, and JEDEC-standard SMA footprint compatibility are critical.
Technical Context
The SM4T18AY uses planar silicon technology to achieve stable breakdown behavior across temperature and low dynamic resistance (0.361 Ω at 25 °C), enabling precise clamping during fast transients like ISO 7637-2 Pulse 3b (+150 V). Its unidirectional configuration provides reverse-biased protection only, making it suitable for DC-biased lines such as battery-supplied ECUs.
It complies with automotive-grade thermal and mechanical standards: UL94 V0 resin housing, 260 °C soldering tolerance, and junction temperature range from –55 °C to +150 °C. The device's voltage-temperature coefficient (αT = 8.8 × 10–4/°C) allows accurate VBR and VCL derating over full operating range.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Stand-off Voltage (VRM) | 15 V - Maximum continuous reverse operating voltage before significant leakage; sets minimum system operating margin. |
| Breakdown Voltage (VBR) | 16.7–18.5 V at 1 mA - Confirmed voltage threshold where avalanche conduction begins; ensures reliable triggering above nominal rail. |
| Clamping Voltage (VCL) | 24.4 V at 16.4 A (10/1000 µs) - Peak voltage seen by protected circuit during worst-case surge; defines maximum stress on downstream ICs. |
| Peak Pulse Power | 400 W (10/1000 µs), 2.3 kW (8/20 µs) - Sustains short-duration energy bursts without failure; enables compliance with ISO 7637-2 Pulse 1 (–150 V). |
| Leakage Current | 0.2 µA at 25 °C, 1 µA at 85 °C - Minimal standby power loss and signal integrity impact in always-on automotive modules. |
| Junction Temperature Range | –55 °C to +150 °C - Supports under-hood deployment in engine control units and transmission controllers without thermal derating. |
Pinout & Package
SM4T18AY is housed in an industry-standard SMA (DO-214AC) surface-mount package per IPC 7531, with JEDEC-registered outline and UL94 V0-compliant epoxy molding compound. The package features two terminals: cathode (marked band) and anode.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Cathode (banded end) | Surge current sink | Connected to protected line; conducts avalanche current to ground during overvoltage events. |
| Anode | Reference node | Typically tied to ground or low-impedance return path; completes clamping loop for unidirectional operation. |
Key Features
| Feature | Design Value |
|---|---|
| AEC-Q101 qualification | Validated for automotive use including temperature cycling, humidity bias, and mechanical shock per JESD22 standards. |
| Low dynamic resistance (RD) | 0.361 Ω at 25 °C - Reduces clamping voltage overshoot during fast-rising transients like ESD contact discharge. |
| High-temperature leakage stability | 1 µA max at 85 °C - Ensures minimal parasitic loading on 12 V battery rails in hot under-hood environments. |
| ISO 7637-2 compliance | Rated for Pulse 1 (–150 V), Pulse 2a (+112 V), Pulse 3a (–200 V), Pulse 3b (+150 V) - Covers all major automotive load-dump and inductive switching threats. |
Applications
| Engine Control Unit (ECU) | CAN Transceiver Protection |
|---|---|
Use Scenario: Protects microcontroller I/O and power supply inputs against load dump and alternator ripple in gasoline/diesel engine management systems. IC Role / Device Role / Timing Role: Unidirectional TVS placed between battery rail and LDO input to clamp negative transients (Pulse 1) and positive spikes (Pulse 2a/3b). Use Value: Limits voltage excursion to ≤24.4 V during –150 V Pulse 1 event, preventing LDO destruction and ensuring ECU boot integrity after ignition cycle. |
Use Scenario: Shields high-speed CANH/CANL differential pair from ESD and coupled noise in vehicle networking gateways. IC Role / Device Role / Timing Role: One SM4T18AY per line (CANH-to-ground, CANL-to-ground) providing asymmetric clamping aligned with common-mode voltage offset. Use Value: Maintains <1 µA leakage at 85 °C to avoid CAN bus bias shift, while clamping 30 kV ESD (IEC 61000-4-2) without signal distortion. |
| Body Control Module (BCM) | Power Window Motor Driver |
Use Scenario: Guards MCU GPIOs and LIN transceiver inputs against cable harness ESD and relay bounce in door module assemblies. IC Role / Device Role / Timing Role: Low-capacitance unidirectional TVS on 12 V supply rail and LIN bus line, leveraging SMA footprint for compact PCB layout. Use Value: Achieves 30 kV air/contact ESD immunity (ISO 10605) without degrading LIN signal rise time due to minimal junction capacitance (<100 pF @ 1 V). |
Use Scenario: Suppresses inductive kickback from brushed DC motor commutation in window lift circuits. IC Role / Device Role / Timing Role: Mounted across motor terminals to absorb back-EMF energy during PWM switching and direction reversal. Use Value: Withstands 2.3 kW (8/20 µs) surge capability, preventing H-bridge MOSFET failure during repeated stall conditions and meeting OEM pulse durability requirements. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar unidirectional automotive TVS diode applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SMAJ18A | Higher clamping voltage (29.2 V @ 13.7 A), lower peak power (400 W same), no AEC-Q101 certification | Not qualified for automotive safety-critical systems; limited to industrial/commercial 12 V applications | Select when AEC-Q101 is not required and higher VCL is acceptable for downstream overvoltage margin. |
| TPSMD18A | Lower leakage (0.5 µA @ 85 °C), identical VBR range, AEC-Q101 qualified, but larger SMB package | Requires more PCB area; less suitable for space-constrained CAN/LIN nodes | Choose when board layout allows SMB footprint and tighter leakage spec is needed for ultra-low-power wake-up circuits. |
Compared with SMAJ18A and TPSMD18A, SM4T18AY uniquely balances AEC-Q101 compliance, SMA footprint density, and 24.4 V clamping performance-making it optimal for CAN/LIN node protection where space, reliability, and precise voltage limiting are jointly constrained.
Availability
SM4T18AY is available at Aetrix Electronics and suitable for automotive ECU design, CAN/LIN bus protection, body electronics development, and power window control systems requiring stable component supply across production lifecycles.
Supply support for SM4T18AY 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
STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, specializing in automotive, industrial, and power management solutions with vertical manufacturing capabilities and broad IP portfolio.
The SM4TY series belongs to ST's automotive-grade transient voltage suppression product line, engineered specifically for ISO 7637-2 and ISO 10605 compliance in 12 V vehicle electrical architectures.
FAQ
Is SM4T18AY bidirectional or unidirectional?
SM4T18AY is a unidirectional TVS diode, configured for reverse-biased operation only. Its cathode is marked with a band and must be connected to the protected line, while the anode connects to ground. This architecture provides optimal clamping for DC-biased automotive rails like 12 V battery supplies and CANH signals.
What is the maximum surge current SM4T18AY can handle?
SM4T18AY supports a peak pulse current of 16.4 A under 10/1000 µs waveform and 32.5 A under 8/20 µs waveform. These values correspond to its 400 W and 2.3 kW peak pulse power ratings respectively, validated per IEC 61000-4-5 and ISO 7637-2 test conditions.
Does SM4T18AY require derating at elevated temperatures?
Yes-its breakdown voltage increases with junction temperature at αT = 8.8 × 10–4/°C, and clamping voltage follows the same trend. At 125 °C, VBR rises ~8.8% above 25 °C value; designers must verify that elevated VCL remains within protected IC's absolute maximum rating under worst-case thermal conditions.
Can SM4T18AY replace SM4T18CAY in a design?
No-SM4T18CAY is the bidirectional variant, capable of clamping both polarities, whereas SM4T18AY only protects against negative transients on positively biased lines. Substitution would leave the circuit vulnerable to positive surges unless topology and grounding scheme are re-evaluated.
SM4T18AY Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Package/Case:
- DO-214AC, SMA
- Series:
- SM4TY, TRANSIL™
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Type:
- Zener
- Unidirectional Channels:
- 1
- Bidirectional Channels:
- -
- Voltage - Reverse Standoff (Typ):
- 15V
- Voltage - Breakdown (Min):
- 16.7V
- Voltage - Clamping (Max) @ Ipp:
- 32.5V
- Current - Peak Pulse (10/1000µs):
- 71A (8/20µs)
- Power - Peak Pulse:
- 400W
- Power Line Protection:
- No
- Applications:
- -
- Capacitance @ Frequency:
- -
- Operating Temperature:
- -55°C ~ 150°C (TJ)
- Grade:
- Automotive
- Qualification:
- AEC-Q101
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- DO-214AC (SMA)
SM4T18AY FAQ
1.How can I place an order for SM4T18AY through Aetrix?
Please submit a Request for Quotation (RFQ) for SM4T18AY 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 SM4T18AY reliable?
The price and inventory of SM4T18AY are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SM4T18AY is usually 5 days.
3.What payment methods are accepted for SM4T18AY?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SM4T18AY transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SM4T18AY?
SM4T18AY orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SM4T18AY 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 SM4T18AY?
For technical support, including SM4T18AY datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SM4T18AY requirements.
6.How does Aetrix verify that SM4T18AY is sourced from the original manufacturer or authorized distributors?
All SM4T18AY 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 SM4T18AY meets industry standards.
7.What is the process for return or replacement of SM4T18AY?
All SM4T18AY units undergo pre-shipment inspection (PSI). If there is an issue with SM4T18AY, 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 SM4T18AY part is unused and in its original packaging.
Return procedure for SM4T18AY:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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