In Atmel USBKEY reference design, they use this to protect the signal lines.
LittleFuse 24V:
But why 24V to protect the 3V to 5V USB lines?
Tyco used to make a 14V, but gave up also:
I have not seen anything with lower voltage. Should I just use some
TI has nice parts TDD2E001 and TPD4E001. Designed to protect USB, FireWire and such.
Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
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They also have clamping voltage of 30V. Does it mean the lines are unprotected between 5V and 30V? Perhaps I am worrying too much, but the "power to be" need to know.
I'ved used 6.2v Zeners without any issues.
Cheers
A 6.7v zener has up to 100pF of capacitance. That is 3.3 ohms at the max rate of USB2.0 (480Mbit/s).
The characteristic impedance of twisted pair is 90 ohms.
Was your product USB1.1 or USB2.0?
Regards, Bob Monsen
Why not use two series low capacitance diodes between the 5V rail and ground. Make sure you have enough and the right kind of capacitance right across the diodes to absorb the blast.
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