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STMicroelectronics SM4T21AY
- Part No.:
- SM4T21AY
- Manufacturer:
- STMicroelectronics
- Category:
- TVS Diodes
- Package:
- DO-214AC, SMA
- Datasheet:
-
SM4T21AY.pdf
- Description:
- TVS DIODE 18VWM 39.3VC SMA
- Quantity:
- Payment:
- Shipping:
Inventory:1,825
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Product details
Overview
SM4T21AY from STMicroelectronics is an AEC-Q101-qualified unidirectional automotive TVS diode in SMA package, designed to clamp transient surges up to 29.2 V (VCL) at 13.7 A (IPP, 10/1000 µs), with 400 W peak pulse power and 0.2 µA leakage at 25 °C. It protects CAN, LIN, and sensor interfaces in 12 V automotive systems against ISO 7637-2 pulses (Pulse 1: −150 V; Pulse 2a: +112 V) and ISO 10605 ESD (±30 kV).
For engineers reviewing the SM4T21AY datasheet, SM4T21AY pinout, SM4T21AY application, or SM4T21AY equivalent, this device delivers validated surge immunity for engine control units, body electronics modules, and ADAS camera power rails - with verified junction temperature operation up to +150 °C and UL94 V0-compliant resin encapsulation.
Technical Context
The SM4T21AY employs planar silicon technology to achieve low dynamic resistance (RD = 0.514 Ω) and stable clamping voltage across temperature (αT = 9.2 × 10−4/°C), enabling consistent overvoltage protection during cold-crank and load-dump events. Its unidirectional configuration supports DC-biased signal lines such as power-supply inputs and sensor analog outputs.
It meets JEDEC-standard SMA mechanical outline (EIAJ ED-7331A), with thermal impedance of 100 °C/W (single pulse, FR4 PCB, 70 µm Cu), and is rated for reflow soldering per IPC/JEDEC J-STD-020 (peak 240–245 °C). The device is not intended for bidirectional AC applications or data-line ESD-only protection without series impedance.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VBR min/max | 20.0 V / 22.2 V at IBR = 1 mA - defines reliable breakdown onset under surge conditions without premature conduction. |
| VCL @ 10/1000 µs | 29.2 V at IPP = 13.7 A - maximum clamped voltage seen by protected IC during standard automotive surge test. |
| PPP | 400 W (10/1000 µs) - sustained energy-handling capability for repetitive load-dump transients in 12 V systems. |
| IR @ VRM | 0.2 µA at 25 °C - ensures negligible standby current draw in always-on vehicle modules (e.g., telematics, alarm controllers). |
| Tj max | +150 °C - enables placement near high-temperature zones (e.g., under-hood ECUs) without derating. |
| ESD rating | ±30 kV contact/air (ISO 10605, C = 150 pF / R = 330 Ω) - exceeds automotive OEM requirements for dashboard and infotainment port protection. |
| Package | SMA (DO-214AC) - surface-mount footprint compatible with automated assembly and IPC-7531-recommended land pattern (5.43 mm × 2.63 mm). |
Pinout & Package
SMA package: molded plastic case with two coplanar gull-wing leads; dimensions per JEDEC MS-013 (EIAJ ED-7331A); total weight 72 mg; UL94 V0-compliant epoxy resin.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Cathode (marked band) | Surge current sink | Connected to protected line (e.g., battery rail); conducts during positive transients to clamp voltage to VCL. |
| Anode | Reference node | Connected to system ground or lower-potential return path; completes conduction loop during overvoltage events. |
Key Features
| Feature | Design Value |
|---|---|
| AEC-Q101 qualification | Validated for automotive under-hood use including temperature cycling, humidity bias, and mechanical shock per stress test plan. |
| Low dynamic resistance (RD) | 0.514 Ω enables tighter clamping margin and reduced power dissipation during multi-pulse events. |
| High Tj operation | +150 °C max junction temperature allows direct placement on hot PCB areas without thermal derating penalties. |
| ISO 7637-2 compliance | Withstands Pulse 1 (−150 V), Pulse 2a (+112 V), Pulse 3a (−200 V), and Pulse 3b (+150 V) without degradation. |
| JEDEC-standard SMA footprint | Enables drop-in replacement with legacy SMA TVS devices and compatibility with existing pick-and-place tooling. |
Applications
| Engine Control Unit (ECU) Power Input | ADAS Camera Module Supply Rail |
|---|---|
|
Use Scenario: Protects 12 V input stage of gasoline/diesel ECU against load dump (ISO 7637-2 Pulse 5a) and alternator ripple. IC Role / Device Role / Timing Role: Unidirectional TVS placed between battery feed and input filter capacitor, clamping transients before LDO regulators. Use Value: Limits VIN to ≤29.2 V during 13.7 A surge, preventing damage to MCU power management ICs rated for 36 V absolute max. |
Use Scenario: Shields 5 V/3.3 V supply to image sensor and SerDes IC in rear-view or surround-view camera. IC Role / Device Role / Timing Role: Secondary protection after upstream fuse and LC filter; handles fast ESD events (ISO 10605 ±30 kV) on power line. Use Value: 0.2 µA leakage avoids measurable impact on always-on camera wake-up current budget (<100 µA). |
| Body Control Module (BCM) LIN Bus | Infotainment Head Unit USB Power Port |
|
Use Scenario: Guards LIN transceiver VCC pin against battery reverse polarity and cranking dips in door module. IC Role / Device Role / Timing Role: Unidirectional clamp referenced to ground; activated only during positive overvoltage, preserving LIN signal integrity. Use Value: 20.0–22.2 V VBR range aligns with 12 V system nominal + tolerance, avoiding false triggering during normal operation. |
Use Scenario: Suppresses conducted transients entering via vehicle USB charging port (e.g., from accessory chargers). IC Role / Device Role / Timing Role: Front-end TVS on 5 V VBUS line, upstream of USB power switch and overcurrent detector. Use Value: 400 W peak power rating sustains multiple 10/1000 µs surges without parameter shift - critical for service-life reliability. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar unidirectional automotive TVS applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SMAJ22A | VBR = 22.2–24.5 V; VCL = 35.5 V @ 11.2 A; PPP = 400 W; no AEC-Q101 qualification. | Lacks automotive qualification and ISO 7637-2 validation; suitable only for industrial or consumer-grade 12 V systems. | Select when AEC-Q101 is not required and higher clamping voltage is acceptable for downstream overvoltage margin. |
| 1.5SMC22A-Q | VBR = 23.1–25.5 V; VCL = 35.5 V @ 11.3 A; PPP = 1500 W; AEC-Q101 qualified; SMC package (larger than SMA). | Higher power rating but larger footprint (7.11 mm × 6.22 mm vs. SMA's 5.35 mm × 4.60 mm); requires PCB layout change. | Select when system-level surge severity exceeds ISO 7637-2 Pulse 5a and board space permits SMC package. |
Compared with SMAJ22A and 1.5SMC22A-Q, SM4T21AY uniquely balances AEC-Q101 compliance, SMA footprint, and precise 21 V VBR targeting - making it optimal for space-constrained, production-grade automotive modules where qualification and layout continuity are mandatory.
Availability
SM4T21AY is available at Aetrix Electronics and suitable for engine control units, ADAS camera modules, body control modules, and infotainment head units requiring stable component supply across automotive production lifecycles.
Supply support for SM4T21AY 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, designing and manufacturing microcontrollers, power management ICs, sensors, and discrete protection devices for automotive, industrial, and consumer markets.
The SM4TxxAY series belongs to ST's automotive-grade TVS portfolio, engineered specifically to meet stringent ISO 7637-2 and ISO 10605 requirements for 12 V and 24 V vehicle electrical systems.
FAQ
Is SM4T21AY bidirectional or unidirectional?
SM4T21AY is a unidirectional TVS diode, indicated by the "AY" suffix (vs. "CAY" for bidirectional). It conducts only during positive overvoltage events relative to ground, making it ideal for DC power rail protection where reverse polarity is blocked by upstream components.
What is the maximum clamping voltage at 8/20 µs surge?
At 8/20 µs waveform, SM4T21AY clamps to 39.3 V with 59 A peak pulse current (IPP). This value is specified in Table 2 of DS6927 Rev 6 and reflects its higher-energy surge capability compared to the 10/1000 µs condition.
Can SM4T21AY replace SM4T22AY in existing designs?
No - SM4T22AY is not a valid ST part number. The closest alternatives are SM4T21AY (VBR = 20.0–22.2 V) and SM4T23AY (VBR = 22.2–24.6 V). Substitution requires verification of VCL margin and system-level surge test compliance due to 1.1 V VBR shift.
Does SM4T21AY require derating above 25 °C ambient?
Yes - while Tj max is +150 °C, peak pulse power must be derated linearly above +25 °C ambient per Figure 3 in DS6927. At +85 °C ambient, PPP drops to ~280 W for 10/1000 µs pulses, based on thermal impedance and PCB copper area.
SM4T21AY 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):
- 18V
- Voltage - Breakdown (Min):
- 20V
- Voltage - Clamping (Max) @ Ipp:
- 39.3V
- Current - Peak Pulse (10/1000µs):
- 59A (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)
SM4T21AY FAQ
1.How can I place an order for SM4T21AY through Aetrix?
Please submit a Request for Quotation (RFQ) for SM4T21AY 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 SM4T21AY reliable?
The price and inventory of SM4T21AY are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SM4T21AY is usually 5 days.
3.What payment methods are accepted for SM4T21AY?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SM4T21AY transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SM4T21AY?
SM4T21AY orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SM4T21AY 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 SM4T21AY?
For technical support, including SM4T21AY datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SM4T21AY requirements.
6.How does Aetrix verify that SM4T21AY is sourced from the original manufacturer or authorized distributors?
All SM4T21AY 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 SM4T21AY meets industry standards.
7.What is the process for return or replacement of SM4T21AY?
All SM4T21AY units undergo pre-shipment inspection (PSI). If there is an issue with SM4T21AY, 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 SM4T21AY part is unused and in its original packaging.
Return procedure for SM4T21AY:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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