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| Low-Noise Front End Protection |
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| Marco:
--- Quote from: Evan.Cornell on February 14, 2020, 07:49:45 pm ---The sensor I'm amplifying is piezoelectric, and can easily generate several volts or more if dropped, knocked, or something like that. Supply rails are +-2.5V, so I need to make sure input pin doesn't exceed voltage rails during an event like that. --- End quote --- It's not about voltage, for a short amount of time it can already take 3kV ... unless the piezo generates enough power to heat up the AD8655 ESD protection to destruction the voltage generated is irrelevant. |
| Evan.Cornell:
--- Quote from: Marco on February 14, 2020, 07:57:17 pm ---It's not about voltage, for a short amount of time it can already take 3kV ... unless the piezo generates enough power to heat up the AD8655 ESD protection to destruction the voltage generated is irrelevant. --- End quote --- I understand that, and the energy profile of piezo pulse is undefined, so I want to operate on the safer side. I am thinking series R = 10ohm or thereabouts with BAV199 to each rail, and another series R ~10ohm before AD8655 input. |
| Kleinstein:
The BAV199 diodes have a rather high forward voltage ( e.g. ~ 1 V), especially with a high current peak. So it would take considerably more than 10 Ohms for protecting the OP. It would likely need more something like 2 of the diodes in series directly parallel to the piezo. This would limit the voltage to some +-1 V without much loading and some +-2.5 V with higher current. For lower leakage current one could use bootstrapping from the amplifier for the 1st. pair of diodes. Chances are the diodes can take enough of a current pulse so one may not need an extra current limiting resistor. |
| Evan.Cornell:
--- Quote from: Kleinstein on February 14, 2020, 08:53:11 pm ---It would likely need more something like 2 of the diodes in series directly parallel to the piezo. --- End quote --- Do you mean like this? |
| Kleinstein:
That would be the minimal version. Another pair of diodes in series to the diodes would be the next step up. |
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