ESD7951ST5G

The ESD7951 from onsemi is a bidirectional ESD protection diode designed for ultra-low capacitance applications. The ESD7951ST5G is the SOD-923 tape-and-reel version with 8000 units per reel. With only 0.5 pF junction capacitance, the device is optimized for high-frequency signal paths where capacitive loading must be minimized — USB 2.0 High-Speed (480 Mbps), HDMI, RF antenna lines, and other impedance-controlled interfaces.

The bidirectional configuration protects signal lines that swing both above and below ground, making it suitable for AC-coupled and differential pair interfaces. The 5 V reverse working voltage (VRWM) covers 3.3 V and 5 V logic rails, while the 12.9 V clamping voltage at 1 A ensures the protected IC sees a limited voltage during an ESD strike.

The SOD-923 package occupies only 0.6 mm² of board area with a 0.5 mm profile, making it one of the smallest ESD protection packages available. This is critical for smartphones, tablets, and wearables where PCB real estate is extremely limited.

The ESD7951 is also available in an automotive-qualified version (SZESD7951ST5G) with AEC-Q101 compliance for automotive applications.

Note: The LCSC listing marks this part as discontinued, but onsemi’s ESD7951 product family remains in production. Verify current availability with authorized distributors before designing into new products.

**Bidirectional TVS Diode Structure:** The ESD7951 uses back-to-back Zener diodes in a single chip, providing symmetric clamping for both positive and negative ESD transients. In normal operation (voltage between -VRWM and +VRWM), both diodes are reverse-biased and draw only leakage current (1 µA max). When a positive transient exceeds VBR, the upper Zener diode avalanches and clamps the voltage. When a negative transient exceeds -VBR, the lower Zener diode conducts.

**Ultra-Low Capacitance Design:** The 0.5 pF capacitance is achieved through a specialized junction geometry that minimizes the depletion region area while maintaining adequate avalanche energy absorption. This is critical for USB 2.0 High-Speed where the specification limits total capacitive loading per D+/D- line.

**Clamping Mechanism:** During an IEC 61000-4-2 ESD event (8 kV contact, 15 kV air), the diode avalanches within sub-nanoseconds, diverting the ESD current away from the protected IC. The clamping voltage (12.9 V at 1 A) represents the voltage the protected device experiences during the event. Lower clamping voltage provides better protection.