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Help with split power operation of AD7176-2 EVAL board

Question asked by pep4130 on Aug 29, 2014
Latest reply on Oct 17, 2014 by pep4130

Good morning, I wish to configure the EVAL board with a split 2.5V power supply.

 

As I delved into the configuration option deeper some questions arose that I would like answered/points I would like confirmed. But first, I will list my list of actions to power the unit with +/-2.5V.

 

A) Power J7 AVDD = +2.5V

B) Power J7 AGND = 0V

C) Power J7 AVSS = -2.5V

D) Power J7 IOVDD = +2.5V (as AVDD2 is not allowed at 3.3V in split mode)

E) Remove links R49, R50, R51, R52 to disconnect AVSS from AGND

F) Set SL1 to 'A'

G) Set SL2 to 'B'

H) Power J4 with VIN - AVSS with 7V?????? See question 2 below

I) Use the ADA4940 for fully diffential input/output

So, my questions are...

 

1) The EVAL UserGuide states that internal reference is +2.5V with reference to AVSS... but as AVSS is now at -2.5V, the reference output is now at sitting about AGND. In this case, should I not use the internal reference?

2) If an external reference is required, can the ADR445 5V off-chip reference be used? (A 7-9V power source between VIN and AVSS is required on J4. This means I have AVSS = REF- via R40 and 5V reference output = REF+

3) Will this configuration give me bipolar operation up to +2^23 and -2^23 bits.

4) When the ADA4940 is used, can DIFF1+ swing +/-2.5V and DIFF2- also swing +/-2.5V?. (Just need an AD expert to confirm this - only that the parametric search on the AD website did not select the AD7176 as bipolar operation. Instead is stated the part as Diff-Uni and SE-Uni... which makes me wonder why a split power supply option is available at all!!!!!

5) I am interfacing to an ATMEL micro via opto-isolators. This outputs of the opto's are 5V TTL. Can I power the output drivers of the opto's from the +/-2.5V rails or do the outputs need to be level translated to +2.5V with reference to AGND (ADC 0V). (I interpreted the datasheet as the latter but I just need someone to confirm this.


Thank you in advance

Pep.



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