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STMicroelectronics SM4T12AY
- Part No.:
- SM4T12AY
- Manufacturer:
- STMicroelectronics
- Category:
- TVS Diodes
- Package:
- DO-214AC, SMA
- Datasheet:
-
SM4T12AY.pdf
- Description:
- TVS DIODE 10VWM 21.7VC SMA
- Quantity:
- Payment:
- Shipping:
Inventory:4,435
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Product details
Overview
SM4T12AY from STMicroelectronics is a unidirectional automotive-grade transient voltage suppression (TVS) diode designed for ISO 7637-2 pulse protection in 12 V battery systems. It features a 12.3 V maximum breakdown voltage (VBR), 17 V clamping voltage (VCL) at 23.5 A peak pulse current (IPP), and 400 W peak pulse power (10/1000 µs) - deployed in engine control units, body electronics, and infotainment power rails.
For engineers reviewing the SM4T12AY datasheet, SM4T12AY pinout, SM4T12AY application, or SM4T12AY equivalent, key selection criteria include its AEC-Q101 qualification, 150 °C junction temperature rating, low 0.2 µA leakage at 25 °C, SMA package compatibility with IPC 7531 footprints, and compliance with ISO 10605 ESD (±30 kV) and ISO 7637-2 surge pulses (Pulse 1, 2a, 3a/b).
Technical Context
The SM4T12AY uses planar silicon technology to achieve stable breakdown characteristics over temperature and low dynamic resistance (RD = 0.201 Ω), enabling precise clamping during fast transients like ISO 7637-2 Pulse 3b (+150 V). Its unidirectional configuration provides reverse-biased surge suppression only, requiring correct polarity placement on DC supply lines.
It operates across -55 °C to +150 °C junction temperature range and maintains clamping performance under repeated surges due to low thermal impedance (Zth(j-a) ≈ 100 °C/W on standard FR4 PCB), validated per JEDEC JESD22-A108 and IEC 61000-4-5 test conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VBR (min–max) | 11.1–12.3 V at IBR = 1 mA: Ensures reliable turn-on before downstream IC damage in 12 V automotive systems. |
| VCL @ IPP | 17 V at 23.5 A (10/1000 µs): Limits voltage seen by protected circuitry during load dump or inductive switching events. |
| IRM max | 0.2 µA at 25 °C / 1 µA at 85 °C: Minimizes standby power loss and avoids false triggering in low-current sensor interfaces. |
| PPP | 400 W (10/1000 µs), 2.3 kW (8/20 µs): Supports both slow battery transients and fast ESD-induced spikes without degradation. |
| Tj max | +150 °C: Enables placement near high-temperature zones (e.g., under-hood ECUs) without derating. |
| Package | SMA (DO-214AC): Industry-standard surface-mount outline per IPC 7531, compatible with automated assembly and reflow profiles up to 245 °C. |
| Standards | AEC-Q101 qualified; ISO 10605 (±30 kV), ISO 7637-2 (Pulse 1/2a/3a/3b); UL94 V0 resin housing. |
Pinout & Package
SMA (DO-214AC) package: Surface-mount, two-terminal device with cathode band marking. Dimensions per JEDEC MS-013 (EIAJ ED-732AA), footprint optimized for thermal dissipation on 70 µm Cu FR4 PCB.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Anode | Input reference node (connected to protected line) | Accepts positive surge energy when reverse-biased; must be placed between source and load on 12 V rail. |
| Cathode | Clamp return path (connected to ground or battery negative) | Provides low-impedance path to sink transient current; requires short, low-inductance trace to chassis ground. |
Key Features
| Feature | Design Value |
|---|---|
| Planar silicon construction | Enables tight VBR tolerance (±5%) and stable leakage across -55 °C to +150 °C operating range. |
| Low dynamic resistance (RD) | 0.201 Ω ensures minimal VCL rise under high IPP, critical for protecting 3.3 V/5 V logic behind LDOs. |
| AEC-Q101 qualification | Validated for automotive under-hood use including temperature cycling, humidity bias, and mechanical shock testing. |
| UL94 V0 epoxy encapsulation | Self-extinguishing housing prevents flame propagation in enclosed modules meeting automotive safety standards. |
| ISO 7637-2 Pulse 3b support | Withstands +150 V transients (t = 100 ms) on 12 V systems without parametric shift or failure. |
Applications
| Engine Control Unit (ECU) Power Input | Body Control Module (BCM) CAN Bus Line |
|---|---|
|
Use Scenario: Protects 12 V input rail of diesel/gasoline ECU against load dump (ISO 7637-2 Pulse 1, -150 V) and alternator ripple. IC Role / Device Role / Timing Role: Primary front-end TVS clamp placed upstream of DC-DC converter and microcontroller power domain. Use Value: Prevents latch-up or permanent damage to MCU and analog front-end ICs during cold-crank or battery disconnect events. |
Use Scenario: Shields CAN_H/CAN_L differential pair in BCM from ESD and coupled transients induced by nearby solenoid switching. IC Role / Device Role / Timing Role: Unidirectional TVS on each CAN line referenced to chassis ground, sized for ±30 kV contact discharge (ISO 10605). Use Value: Maintains CAN signal integrity below 1 V overshoot during 8/20 µs surges, avoiding bus arbitration errors or node reset. |
| Infotainment Head Unit Power Supply | ADAS Camera Module Interface |
|
Use Scenario: Guards 12 V-to-5 V/3.3 V power conversion stage in head unit against ignition noise and jump-start surges. IC Role / Device Role / Timing Role: Secondary protection after fuse and primary LC filter, placed adjacent to buck controller input capacitor. Use Value: Limits VIN to ≤17 V during 10/1000 µs transients, preventing overvoltage shutdown of PMIC and preserving boot sequence reliability. |
Use Scenario: Protects FPD-Link III or GMSL serial interface lines in rear-view camera module from cable-induced ESD and hot-swap transients. IC Role / Device Role / Timing Role: Low-capacitance (<100 pF) TVS on data lines, leveraging SMA's minimal parasitic capacitance at 1 MHz. Use Value: Clamps transients within 1 ns response time while adding <0.3 pF capacitance per line, preserving 3 Gbps video signal integrity. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar unidirectional TVS diode applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SMAJ12A | Higher VCL = 19.9 V at 20.1 A; lower PPP = 400 W but no AEC-Q101 qualification. | Not suitable for automotive production; limited to industrial/commercial 12 V systems. | Select only if AEC-Q101 is not required and board space allows larger SMAJ footprint. |
| 1.5SMC12A | Same VBR range but SMC package (DO-214AB); higher thermal mass but larger footprint (7.11 × 6.22 mm vs SMA 4.8 × 2.7 mm). | Preferred where higher surge endurance (>5000 cycles) is needed, but incompatible with dense automotive PCB layouts. | Choose when long-term reliability under repeated surges outweighs size constraints and AEC-Q101 is secondary. |
Compared with SMAJ12A and 1.5SMC12A, SM4T12AY delivers automotive-grade reliability in the smallest qualified footprint, with tighter VBR tolerance and lower leakage - essential for modern low-power, high-density ECU designs.
Availability
SM4T12AY is available at Aetrix Electronics and suitable for engine control units, body control modules, infotainment head units, and ADAS camera modules requiring stable component supply across automotive production lifecycles.
Supply support for SM4T12AY 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.
The SM4TxxAY series belongs to ST's automotive-qualified TVS portfolio, engineered specifically for robust transient immunity in 12 V/24 V vehicle electrical architectures per ISO 7637-2 and ISO 10605 requirements.
FAQ
What is the maximum clamping voltage of SM4T12AY under a 10/1000 µs surge?
The SM4T12AY clamps to 17 V at 23.5 A peak pulse current for a 10/1000 µs waveform, as specified in Table 2 of DS6927 Rev 6. This value is measured at Tamb = 25 °C with initial junction temperature equal to ambient, and remains stable up to Tj = 150 °C due to its low αT temperature coefficient (7.8 × 10−4/°C).
Is SM4T12AY bidirectional or unidirectional?
SM4T12AY is a unidirectional TVS diode, indicated by the "AY" suffix (vs "CAY" for bidirectional). It conducts only in reverse bias - anode connected to protected line, cathode to ground - and blocks forward voltage up to 1 V at 10 mA, making it suitable for DC power rail protection.
Can SM4T12AY replace SM4T12CAY in a design?
No - SM4T12AY and SM4T12CAY have different polarity configurations. The "AY" version is unidirectional and must be oriented with cathode to ground; the "CAY" version is bidirectional and symmetrical. Substitution requires schematic and layout revision to accommodate polarity and clamping behavior differences.
What is the recommended PCB footprint for SM4T12AY?
The recommended SMA footprint matches Figure 18 in DS6927 Rev 6: 5.43 mm pad length × 1.40 mm pad width, with 2.63 mm center-to-center spacing and 1.64 mm solder mask opening. Copper area ≥1 cm² per pad reduces Rth(j-a) to <80 °C/W, improving surge endurance beyond 400 W ratings.
SM4T12AY 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):
- 10V
- Voltage - Breakdown (Min):
- 11.1V
- Voltage - Clamping (Max) @ Ipp:
- 21.7V
- Current - Peak Pulse (10/1000µs):
- 106A (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)
SM4T12AY FAQ
1.How can I place an order for SM4T12AY through Aetrix?
Please submit a Request for Quotation (RFQ) for SM4T12AY 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 SM4T12AY reliable?
The price and inventory of SM4T12AY are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SM4T12AY is usually 5 days.
3.What payment methods are accepted for SM4T12AY?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SM4T12AY transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SM4T12AY?
SM4T12AY orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SM4T12AY 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 SM4T12AY?
For technical support, including SM4T12AY datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SM4T12AY requirements.
6.How does Aetrix verify that SM4T12AY is sourced from the original manufacturer or authorized distributors?
All SM4T12AY 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 SM4T12AY meets industry standards.
7.What is the process for return or replacement of SM4T12AY?
All SM4T12AY units undergo pre-shipment inspection (PSI). If there is an issue with SM4T12AY, 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 SM4T12AY part is unused and in its original packaging.
Return procedure for SM4T12AY:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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