Is the ESD and overvoltage protection for my ADC circuit sufficient?

I am currently building a data logging device for monitoring battery packs which contain 8 Lithium cells. The device will periodically log the voltages of all 8 cells, as well as log temperatures collected from 3 thermistors. My device has an STM32L series microcontroller.

As of now I am trying to figure out what the input circuit for the ADC should be. Due to the high power nature of the system, and it containing two large industrial motors which are subject to varying loading, I am assuming the battery pack would be subjected to high voltage and current spikes. I will be taking taps from each cell and connecting it to my device.

In terms of protection, I have done some research and found I should probably be looking into TVS and clamping diodes as protection means. The input range that needs to be measured is 0-32V. I have guesstimated the following circuit:

The TVS diode is SMAJ33A (http://www.littelfuse.com/~/media/electronics/datasheets/tvs_diodes/littelfuse_tvs_diode_smaj_datasheet.pdf.pdf) with a standoff voltage of 33V, and maximum clamping voltage of 53.3V @ 7.5A (Ipp). I am not sure how to select the TVS diode (or if I even need one!), so I would really appreciate any advice on this. For the clamping diode part, I am following ADC input protection?. I have selected Bat54S dual Schottky barrier diodes. This is to hopefully provide over voltage protection.

Do you think my choice of circuit protection is sufficient for this application? Any advice would be really appreciated. Thanks!

Answer

The most important component that needs to be there is R1 and it is 100 k ohm so you're good to go. Any IC including the AD820 will have ESD protection diodes at it's input already. You added additional BAT54 diodes in parallel to them, that will not hurt but they're not really needed either.

Those internal (on chip) ESD diodes will protect the chip sufficiently as long as you limit the current, which you do with R1.

The TVS D2 will only offer additional protection as long as there is something (like series resistance) present to limit the current. If the input voltage is enough to make D2 conduct but the current itsn't somehow limited, D2 will self distruct.

So: all in all your schematic looks fine to me, you could remove some components if you want to save cost but it will also work as it is now.