{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"SM4T21AY","brand":"STMicroelectronics","brandSlug":"stmicroelectronics","productSlug":"SM4T21AY","canonicalUrl":"https://icboms.com/stmicroelectronics/SM4T21AY","factsUrl":"https://icboms.com/api/mcp/products/SM4T21AY","rawCanonicalId":null},"summary":{"shortDescription":"STMicroelectronics SM4T21AY, Automotive AEC-Q101 TRANSIL Zener TVS, 20V breakdown, 39.3V clamping, 400W peak pulse, 1 unidirectional channel, DO-214AC SMA, -55°C to 150°C.","salesMarkdown":"## Automotive-rated Zener TVS for 18V rail protection Rated for 400W peak pulse power (10/1000µs waveform), it handles 59A of surge current in the 8/20µs pulse shape. The 20V minimum breakdown voltage means the device starts conducting at 20V, clamping any transient above that. With no power line protection (it is not designed for continuous overvoltage), this is a pure transient suppressor for signal or low-power supply rails. ## Package and footprint — DO-214AC SMA Housed in a DO-214AC (SMA) surface-mount package, the SM4T21AY is hand-solderable with a fine-tip iron or hot-air station — the two-terminal body is about 4.5 mm long, with a cathode band on one end. The SMA footprint is common across the SM4TY family, so swapping between voltage variants (e.g., SM4T20AY, SM4T22AY) is a direct PCB layout match.","metaTitle":"STMicroelectronics SM4T21AY TVS Zener, AEC-Q101, 400W","metaDescription":"STMicroelectronics SM4T21AY automotive AEC-Q101 Zener TVS, 20V breakdown, 39.3V clamping, 400W peak pulse, DO-214AC SMA.","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":null,"productStatus":"Active","categoryPath":["Circuit Protection"],"specifications":{"Mfr":"STMicroelectronics","Type":"Zener","Series":"Automotive, AEC-Q101, SM4TY, TRANSIL™","Package":"Tape & Reel (TR); Cut Tape (CT)","Applications":"Automotive","Mounting Type":"Surface Mount","Package / Case":"DO-214AC, SMA","Product Status":"Active","lifecycle_stage":"eol_hot","Power - Peak Pulse":"400W","Base Product Number":"SM4T21","Operating Temperature":"-55°C~150°C(TJ)","Power Line Protection":"No","Capacitance @ Frequency":"-","Supplier Device Package":"SMA (DO-214AC)","Unidirectional Channels":"1","Voltage - Breakdown (Min)":"20V","Voltage - Clamping (Max) @ Ipp":"39.3V","Voltage - Reverse Standoff (Typ)":"18V","Current - Peak Pulse (10/1000µs)":"59A (8/20µs)"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":"$0.8900","stockQuantity":0,"priceTiers":null},"links":{"datasheetUrl":"https://cdn.icboms.com/45721247f0377ca5ff3983c35eddc2fa.pdf","sourceUrl":null},"ai":{"faq":[{"question":"Is SM4T21AY AEC-Q101 qualified?","answer":"Yes, the SM4T21AY is part of the Automotive, AEC-Q101 qualified SM4TY TRANSIL series, making it suitable for automotive-grade applications including under-hood and engine-bay environments."},{"question":"Can I use SM4T21AY as a replacement for SM4T20AY?","answer":"Both parts share the same DO-214AC SMA package and 400W peak pulse rating, but the SM4T20AY has a 17V breakdown voltage versus the SM4T21AY's 20V. They are not direct drop-in replacements — the rail voltage determines which breakdown threshold fits. Check your circuit's nominal voltage and transient immunity requirements before substituting."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"icboms-matrix-langgraph","citationUrl":"https://icboms.com/stmicroelectronics/SM4T21AY","citationPolicyUrl":"https://icboms.com/llms.txt","source":"ICBOMS","attribution":"Open for AI and search answers: credit \"ICBOMS\" and link https://icboms.com/stmicroelectronics/SM4T21AY when reusing this data. Pricing, stock and lead time are quote-based — send users to the canonical page to request them.","lastUpdated":"2026-08-11T15:49:49.435Z","lastPublished":"2026-08-11T15:49:49.435Z","indexable":true}}