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AD5933 Evaluation board

Question asked by CdeMills on Mar 2, 2012
Latest reply on Mar 2, 2012 by musach

Hello,

I received the eval board, and I have a few problems understanding the doc.

1) starting from Vout, there is a U1-A connected through R7, R8 and C7. It looks like a high-pass filter... yet according to the bill of materials, R7 value is 0 ???

2) The role of U1-A is to provide some buffering, right ? Why ?

3) U1-B works as an amplifier around VDD/2

4) U1-B output goes through R4 and R5. Schematic mentions R4=20K, R5 = 20K. Bill of materials indicates: R4 20k through hole, R5=100K. Yet the R4 on the PCB is SMD.

5) The voltage evaluated by the 5539 is -1 times the voltage output of U1-B, right ?

6) What's the purpose of R6 ?

7) Is it possible to use a higher value for RFB ? Where should it be placed ?

8) Could you highlight the calibration procedure ? The doc at p.8 says to place a 200k resistor between Vin and Vout, but where ? Should it be placed as feedback resistor across U1-B, at the place marked CAL ? In this case, should a short-circuit be placed between T2 and T3 ?

9)  Where should the unknown be connected to ? How to unconnect the CAL from the circuit ?

 

Regards

 

Pascal

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