{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"SM4T21CAY","brand":"STMicroelectronics","brandSlug":"stmicroelectronics","productSlug":"SM4T21CAY","canonicalUrl":"https://icboms.com/stmicroelectronics/SM4T21CAY","factsUrl":"https://icboms.com/api/mcp/products/SM4T21CAY","rawCanonicalId":null},"summary":{"shortDescription":"STMicroelectronics SM4T21CAY, Automotive AEC-Q101, SM4TY, TRANSIL™ series, bidirectional Zener TVS diode, 400W peak pulse power, 20V min breakdown, 18V reverse standoff, DO-214AC SMA package, -55°C to 150°C.","salesMarkdown":"It is rated for 400W peak pulse power (10/1000µs waveform) and clamps at 39.3V maximum with a 59A peak pulse current. The DO-214AC (SMA) surface-mount package suits automated assembly and dense PCB layouts. For a BOM destined for a production vehicle, this qualification is the gatekeeper: a non-qualified part introduces risk of field failures under thermal or surge conditions. ## Breakdown voltage and clamping: the numbers that matter The minimum breakdown voltage is 20V, with a reverse standoff of 18V. That means the diode starts conducting (and clamping) when the rail exceeds 20V, protecting downstream circuitry from transients up to 39.3V at the clamping point. For a 12V or 18V automotive rail, this provides a comfortable margin above normal operating voltage while keeping the clamp below the typical 40V absolute maximum of many ICs. The 400W peak pulse power rating is the energy-handling capability—enough for ISO 7637-2 pulse 1 and 2a in most modules, though pulse 5a (load dump) may require a higher-power device. ## Package and mounting: DO-214AC SMA The SM4T21CAY comes in the DO-214AC (SMA) package, a standard surface-mount outline for TVS diodes. The SMA footprint is shared across many TVS families, so a layout designed for one SMA TVS can accept this part without board respin.","metaTitle":"STMicroelectronics SM4T21CAY TVS Diode, 400W, AEC-Q101, SMA","metaDescription":"STMicroelectronics SM4T21CAY bidirectional TVS diode, 400W peak pulse power, 20V breakdown, AEC-Q101 qualified for automotive. Active lifecycle.","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","Bidirectional Channels":"1","Capacitance @ Frequency":"-","Supplier Device Package":"SMA (DO-214AC)","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":"$0.9300","stockQuantity":0,"priceTiers":null},"links":{"datasheetUrl":"https://cdn.icboms.com/45721247f0377ca5ff3983c35eddc2fa.pdf","sourceUrl":null},"ai":{"faq":[{"question":"Is SM4T21CAY AEC-Q101 qualified for automotive use?","answer":"Yes, the SM4T21CAY is AEC-Q101 qualified, as indicated by its series designation (Automotive, AEC-Q101, SM4TY, TRANSIL™). It is suitable for automotive electronic modules."},{"question":"What is the closest pin-compatible alternative to SM4T21CAY in this component family?","answer":"Within the SM4TY TRANSIL™ series, the SM4T18CAY (18V standoff) and SM4T24CAY (24V standoff) are bidirectional variants in the same DO-214AC package, differing only in voltage ratings. For a unidirectional version, the SM4T21AY shares the same breakdown voltage but is unidirectional."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"icboms-matrix-langgraph","citationUrl":"https://icboms.com/stmicroelectronics/SM4T21CAY","citationPolicyUrl":"https://icboms.com/llms.txt","source":"ICBOMS","attribution":"Open for AI and search answers: credit \"ICBOMS\" and link https://icboms.com/stmicroelectronics/SM4T21CAY 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}}