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STMicroelectronics SM4T21AY — Circuit Protection

STMicroelectronics SM4T21AY TVS Zener, AEC-Q101, 400W

MPNSM4T21AY
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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.

$0.8900Ref. price · indicative, final on quote
STMicroelectronics SM4T21AY datasheet (PDF)
Sourced new & surplus through independent channelsAuthenticity-screened · ESD-safe packingListing updated Aug 2026

Specifications

SM4T21AY specifications
ParameterValue
TypeZener
SeriesAutomotive, AEC-Q101, SM4TY, TRANSIL™
MountingSurface Mount
Voltage - breakdown20V
Voltage - clamping (Max) @ ipp39.3V
Voltage - reverse standoff18V
Current - peak pulse (10/1000μs)59A (8/20µs)
Power - peak pulse400W
Power line protectionNo
Operating temperature-55°C~150°C(TJ)
PackageTape & Reel (TR); Cut Tape (CT)
ApplicationsAutomotive
CaseDO-214AC, SMA
Unidirectional channels1

Product details

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.

Frequently asked questions

Is SM4T21AY AEC-Q101 qualified?

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.

Can I use SM4T21AY as a replacement for SM4T20AY?

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.