Zener diode adc protection

[scarrier]

I saw in a reference design : ( http://www.maximintegrated.com/app-notes/index.mvp/id/4663 ) on Figure 8, They put BAT54 30V zener  diode, i don't understand what purpose do they serve. From what understand from the question at the end is that they use the reverse voltage, how do they clamp.

[Marco]

From what understand from the question at the end is that they use the reverse voltage

Maybe it would be more helpful to read the answer rather than the question ...

"The reverse 30V breakdown voltage is incidental."

So, they use the forward voltage.

how do they clamp.

A zener diode is still a diode, with a forward voltage it acts just like a diode ... when V-foward is exceeded it rapidly starts conducting more current. With Vf in this case being around 0.3 Volt, so the input voltage on the ADC pins is clamped to -0.3 volt on the low end.

[c4757p]

BAT54 is Schottky, not Zener.