ADAU1701 max ratings/protection on adc

Hello,

Funny, the data sheet shows absolute maximum ratings for the digital inputs but not the ADC. Please refer to the post at https://ez.analog.com/message/64012#64012 -- where SteveL suggests that the ADC does have similar ESD clamps.

I can't help but notice that the ADAU1701MINIZ eval board has no input protection other than its 10 K series resistors (10K rather than 18 K for more input sensitivity). Mine has worked for years with all sorts of strange inputs. However, the common wisdom is to employ protection like that shown below:

Here the diodes clamp at about 0.5 V beyond the rails. With the -1701's internal diodes clamping at about 0.3 V, this places 0.2 V across the chip's built-in input resistance. As a result, 100 uA flows in or out of the pin. This being in the same league as the normal operating current, the input remains protected.

Where I work we have used this scheme successfully in hundreds of units. We have also employed a more complex version where the 18 K resistor is split in half, placing 9 K each before and after the diodes. This may be overkill, however. The best protection scheme depends upon what inputs are expected in use.

Best regards,

Bob

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EZ Admin