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ADA2200 Test Circuit

Question asked by Jls62 on Dec 31, 2017
Latest reply on Jan 29, 2018 by Jls62

Based on a consult with Brian Harrington about 18 months ago, I have proceeded to incorporate the ADA2200 into my design to reverse engineer a spinner magnetometer that had used tube technology.  I am a volunteer for the Office of Archaeological Services, Department of Cultural Affairs, New Mexico. I have included a schematic of the project as it stands now. Everything seems to work as Brian suggested it might, but now I am trying to test the ADA2200 EVALZ unit individually before completing the draft design and testing it. The test schematic is also included. It is based on the UG-702, ADA2200-EVALZ User Guide, Figure 2. The original test circuit didn’t seem appropriate for my use as I needed to evaluate the response to signals out of phase with the CLOCKIN signal. The RC network accomplishes this and phase can be adjusted by changing the signal generator frequency while adjusting the generator output for a constant input to the ADA2200. In the design the ADA2200 is proceeded by an AD8476 as Brian had suggested.

 

When a signal is applied the output between pins 7 and 8 slowly increases until it reaches saturation just below +3.3 volts. Changing the frequency in put or amplitude has no effect. I have the VOCM connected as in the original Figure 2. I have measured the power supply voltage (+3.3 volts) and VOCM (+1.65 volts) and they are as expected. There are two issues as I see it:

 

  1. I did not design or setup the test circuit correctly.
  2. ESD or some other defect has damaged the circuit so it no longer works as designed. (I have tried to be careful to prevent creating ESD while working with the circuit.)

 

Do you have any ideas as to why this is not working as I expected. If ESD or some other situation has destroyed the circuit how fast is it possible to get a replacement? My original order took about 6 weeks and I would prefer not to wait that long a second time. If a replacement is not readily available can the circuit be repaired?

 

Your help in getting me back on course would be very much appreciated.

 

Thanks again,

 

Jack Ellis

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