400 W peak pulse power in an SMA footprint
It sits in the standard DO-214AC (SMA) surface-mount package, rated for 400 W peak pulse power (10/1000 µs waveform) and capable of handling 106 A peak pulse current under the 8/20 µs test condition. The reverse standoff voltage is 10 V, with a minimum breakdown of 11.1 V and a maximum clamping voltage of 21.7 V at the rated peak current.
AEC-Q101 and the -55 to 150 °C range
The AEC-Q101 qualification means this diode is screened for the stress tests automotive Tier-1s require — high-temperature reverse bias, temperature cycling, and humidity bias.
Date-code and marking consistency
The SM4T12AY is marked with ST's standard TRANSIL™ laser etch on the SMA body. For a buyer screening gray-market lots, the date-code font, pad geometry, and package flash should match ST's published marking layout for the SM4TY series. Any deviation — mismatched font weight, off-center laser, or inconsistent top-side ink — flags a potential re-mark. Physical authentication (decapsulation, X-ray) confirms the die matches the 400 W Zener structure, not a lower-rated die swapped in.