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Signal input ranges on ADAS3023

Question asked by gimbalguy on Mar 23, 2015
Latest reply on Feb 16, 2017 by Gnib

I am confused about the specification in the datasheet identifying the input ranges.  The other posts on this component do not address this particular question on the topic.  My application is a bipolar single ended signal which has a range of ±12V, common mode of 0V.  Notwithstanding these values, I note that the input range for one of the PGIA settings is +/-20.48V.  Why and how is this possible when the maximum input to the signal pins is 2.5V less than the supply rails?  (Datasheet pg 3)  These supply rails are limited to +/- 16.5V in the absolute max. (Datasheet pg 9)  That would suggest that the absolute maximum is +/- 14V for signal inputs.  Nominally, these max values would be +/-12.5V based on a +/-15V power supply input.  My hardware is designed and I am designing my VHDL to interface while I wait for the hardware to arrive.  If I need to modify my hardware, it would be nice to know before it arrives so that I might have the chance to make necessary modifications.

 

Based on, say the PGIA setting for a 20.48V which best matches my input range, where does my input value saturate?  At +/-12.5V?  How would a +/-20.48V range be supported in this case without the ESD diodes conducting?

 

I am estimating that the transfer function (positive side for this argument's sake) would be:

 

CODE = Vin/Vref * PGIA * 32767.

 

Thanks in advance.

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