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STMicroelectronics SM4T21CAY
- Part No.:
- SM4T21CAY
- Manufacturer:
- STMicroelectronics
- Category:
- TVS Diodes
- Package:
- DO-214AC, SMA
- Datasheet:
-
SM4T21CAY.pdf
- Description:
- TVS DIODE 18VWM 39.3VC SMA
- Quantity:
- Payment:
- Shipping:
Inventory:3,809
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Product details
Overview
SM4T21CAY from STMicroelectronics is a bidirectional automotive-grade transient voltage suppression (TVS) diode in SMA package, designed to protect 12 V/24 V automotive electronics against ISO 7637-2 pulses (Pulse 1: −150 V; Pulse 2a: +112 V; Pulse 3a: −200 V; Pulse 3b: +150 V) and ISO 10605 ESD events (±30 kV air/contact). It features 21.1 V nominal breakdown voltage (VBR), 29.2 V clamping voltage (VCL) at 13.7 A (10/1000 µs), and 39.3 A peak pulse current (IPP) under 8/20 µs surge.
For engineers reviewing the SM4T21CAY datasheet, SM4T21CAY pinout, SM4T21CAY application, or SM4T21CAY equivalent, this device is selected for robust front-end protection in CAN/LIN bus interfaces, body control modules, and power supply inputs where low leakage (<1 µA at 85 °C), AEC-Q101 qualification, and 150 °C junction operation are mandatory.
Technical Context
The SM4T21CAY implements a planar silicon avalanche structure optimized for high-reliability automotive environments. Its bidirectional configuration enables symmetrical clamping for both positive and negative transients without polarity dependency, and its low dynamic resistance (RD = 0.514 Ω at 25 °C) ensures minimal voltage overshoot during fast 8/20 µs surges.
It complies with ISO 7637-2 (Pulse 1, 2a, 3a, 3b) and ISO 10605 (150 pF/330 Ω and 330 pF/330 Ω), and operates across −55 °C to +150 °C junction temperature. The device's thermal impedance (Zth(j-a)) is characterized for standard FR4 PCB footprints, supporting stable power dissipation up to 400 W (10/1000 µs) at Tj = 25 °C.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VBR (min/typ/max) | 20.0 / 21.1 / 22.2 V - Ensures reliable turn-on before system-level overvoltage damage occurs in 12–24 V automotive rails. |
| VCL @ IPP (10/1000 µs) | 29.2 V at 13.7 A - Limits downstream IC voltage stress to safe levels during slow surges like load dump. |
| VCL @ IPP (8/20 µs) | 39.3 V at 59 A - Clamps fast ESD and coupled noise transients while maintaining signal integrity. |
| IR @ VRM | 0.2 µA at 25 °C, 1 µA at 85 °C - Enables use in high-impedance sensor bias networks without leakage-induced offset error. |
| PPP (10/1000 µs) | 400 W - Sustains repeated surge events in engine control units without parametric shift or failure. |
| Tj max | +150 °C - Supports placement near hot components (e.g., power MOSFETs, DC-DC converters) without derating. |
| AEC-Q101 qualified | Qualified per stress test conditions including HTOL, TC, UHAST, and ESD - meets automotive reliability requirements for safety-critical systems. |
Pinout & Package
SM4T21CAY is housed in an industry-standard SMA (DO-214AC) surface-mount package per JEDEC outline and IPC-7531 footprint. The package uses planar construction for low parasitic capacitance and high thermal stability.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Anode (Cathode side marked) | Surge current return path for negative transients | Bidirectional symmetry means either terminal serves as cathode/anode depending on polarity - no orientation sensitivity in layout. |
| Cathode (marked band) | Surge current sink for positive transients | Marking identifies the cathode end; however, due to bidirectional design, both terminals conduct equally in reverse bias. |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional clamping | Enables single-device protection of AC-coupled lines (e.g., CAN H/L) without external polarity management. |
| Low dynamic resistance (RD) | 0.514 Ω at 25 °C - Reduces clamping voltage rise under high-current surges, improving margin for downstream 3.3 V/5 V logic. |
| AEC-Q101 qualification | Validated for automotive under-hood and cabin applications - eliminates need for additional qualification testing by OEMs. |
| UL94 V0-compliant resin | Ensures flame-retardant encapsulation required for automotive interior and battery-connected assemblies. |
| High Tj operation (+150 °C) | Supports mounting directly on power supply PCBs near heat sources without thermal derating penalties. |
Applications
| Automotive Body Control Module (BCM) | CAN FD Transceiver Protection |
|---|---|
|
Use Scenario: Protects microcontroller I/O and power rails in BCMs exposed to load dump and jump-start transients. IC Role / Device Role / Timing Role: Front-end TVS clamp placed between fuse and LDO input, absorbing energy before it reaches sensitive regulators and MCU pins. Use Value: Prevents latch-up or permanent damage during ISO 7637-2 Pulse 1 (−150 V) and Pulse 2a (+112 V), enabling >10-year field reliability. |
Use Scenario: Shields CAN FD physical layer transceivers from ESD and coupled noise on vehicle harnesses. IC Role / Device Role / Timing Role: Bidirectional shunt device across CAN_H/CAN_L differential pair, clamping common-mode surges without disrupting data integrity. Use Value: Maintains <100 pF junction capacitance at 0 V bias, preserving signal edge rate and bit error rate compliance up to 5 Mbps. |
| 12 V Battery Monitoring Circuit | Automotive LIN Bus Node |
|
Use Scenario: Safeguards analog front-end of battery voltage/current sensors connected directly to 12 V rail. IC Role / Device Role / Timing Role: Low-leakage (0.2 µA @ 25 °C) TVS placed upstream of precision voltage dividers and ADC inputs. Use Value: Avoids measurement drift caused by leakage current injection into high-impedance sensing nodes, ensuring ±0.5% accuracy over temperature. |
Use Scenario: Protects LIN transceiver and microcontroller UART pins in door modules and seat controllers. IC Role / Device Role / Timing Role: Unidirectional/bidirectional TVS on LIN bus line and VCC rail, rated for 21 V standoff to tolerate battery ripple. Use Value: Survives repeated ±30 kV ESD contact discharges per ISO 10605 while maintaining <1 µA leakage at 85 °C for low-power sleep mode. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar TVS diode applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SMAJ22CA | Unidirectional, 22 V VBR, 35.5 V VCL @ 11.2 A (10/1000 µs), 400 W rating | Lacks bidirectionality - requires dual-device implementation for AC lines like CAN; not AEC-Q101 qualified | Select only for non-automotive, cost-sensitive industrial designs where bidirectional clamping is unnecessary. |
| TPSMD22C | Bidirectional, 22 V VBR, 33.2 V VCL @ 12 A (10/1000 µs), 400 W, AEC-Q101 qualified | Lower RD (0.38 Ω) yields tighter clamping but higher leakage (1.5 µA @ 85 °C) | Prefer when clamping voltage margin is critical and leakage tolerance allows ≥1.5 µA at elevated temperature. |
Compared with SMAJ22CA and TPSMD22C, SM4T21CAY delivers optimal balance of AEC-Q101 compliance, bidirectional capability, ultra-low leakage (<1 µA at 85 °C), and predictable clamping (29.2 V @ 13.7 A), making it the preferred choice for automotive CAN, LIN, and battery-sensing nodes requiring long-term stability.
Availability
SM4T21CAY is available at Aetrix Electronics and suitable for automotive body control modules, CAN FD interface protection, and battery monitoring circuits requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for SM4T21CAY 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 devices, sensors, and protection components for automotive, industrial, and consumer markets.
The SM4Txx series belongs to ST's automotive-grade TVS portfolio, engineered specifically to meet stringent ISO 7637-2 and ISO 10605 immunity requirements in harsh vehicle electrical environments.
FAQ
What is the marking code for SM4T21CAY?
The top-side marking for SM4T21CAY is "DBQY", as specified in ST's DS6927 Rev 6 ordering information table. This two-letter prefix ("DB") followed by "QY" uniquely identifies the 21 V bidirectional variant in SMA packaging and is laser-etched on the cathode-end surface of the device.
Can SM4T21CAY replace SM4T22CAY in existing designs?
No - SM4T22CAY is not a valid ST part number. The closest standard variants are SM4T21CAY (21.1 V VBR) and SM4T23CAY (23.4 V VBR). Substitution requires verification of system-level clamping margin, as VCL increases by ~2.8 V between these grades; direct replacement may compromise surge immunity or cause false triggering.
Does SM4T21CAY support reflow soldering per J-STD-020?
Yes - ST specifies a peak reflow temperature of 240–245 °C for 2–3 seconds, with ramp rates ≤3 °C/s pre-peak and ≤6 °C/s cooling, fully compliant with IPC/JEDEC J-STD-020 Class 3 moisture sensitivity level (MSL 1). The SMA package is rated for unlimited floor life when sealed per JEDEC standards.
Is SM4T21CAY suitable for 48 V mild-hybrid systems?
No - its 22.2 V maximum VBR and 39.3 V VCL are insufficient for 48 V rail protection. For 48 V systems, ST recommends SM4T47CAY (49 V VBR, 64.5 V VCL) or SM4T56CAY (58.9 V VBR, 77.4 V VCL), both AEC-Q101 qualified and validated for ISO 7637-2 Pulse 1 up to −400 V in 48 V architectures.
SM4T21CAY 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:
- -
- Bidirectional Channels:
- 1
- 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)
SM4T21CAY FAQ
1.How can I place an order for SM4T21CAY through Aetrix?
Please submit a Request for Quotation (RFQ) for SM4T21CAY 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 SM4T21CAY reliable?
The price and inventory of SM4T21CAY are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SM4T21CAY is usually 5 days.
3.What payment methods are accepted for SM4T21CAY?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SM4T21CAY transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SM4T21CAY?
SM4T21CAY orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SM4T21CAY 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 SM4T21CAY?
For technical support, including SM4T21CAY datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SM4T21CAY requirements.
6.How does Aetrix verify that SM4T21CAY is sourced from the original manufacturer or authorized distributors?
All SM4T21CAY 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 SM4T21CAY meets industry standards.
7.What is the process for return or replacement of SM4T21CAY?
All SM4T21CAY units undergo pre-shipment inspection (PSI). If there is an issue with SM4T21CAY, 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 SM4T21CAY part is unused and in its original packaging.
Return procedure for SM4T21CAY:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SM4T21CAY Tags
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