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AD5934(EVAL-CN0349) output frequency problem

Question asked by Glanthor on Nov 24, 2017
Latest reply on Feb 16, 2018 by Snorlax

Dear All,

 

I have some problem with the output frequency on my EVAL-CN0349 board. I found out this problem in connection of my other issue(Measure conductivity below 25us with EVAL-CN0349 (AD5934) ).

So I measured the output frequency on my eval board and it seems that it cannot genarate the proper output frequency. The voltage is proper. So I started to debug my code to see if I made any mistakes. I found one and corrected it, now I can set the system clock bit in the control register just fine. The start frequency code is calculated and written into the device properly. I checked it. 
I want to set 30kHz but I only get  around 6kHz in case of internal clock(today I will try to measure the output frequency at more setpoints and I will refresh this post), the frequency increment works but also not properly. The device increments the frequency but not with the given value it seems. 

 

I started to read some discussions on the forums and I found the next:

 

AD5933: Initialize With Start Frequency Command Not Working 
in which snorlax states the following:

Also make sure that the chip is not the AD5934 - the version that does not have the internal oscillator. 

 

Now these confused me. Can somebody help me to clarify this?

Is there internal 16MHz clock in the AD5934? (According to its datasheet yes, and my setup works with the internal clock setting just the frequency is not proper)

 

As the  documentation of the circuit states(http://www.analog.com/media/en/reference-design-documentation/reference-designs/CN0349.pdf ) :

 

The frequency of the clock applied to the MCLK pin is set to
1 MHz using a stable, low jitter, FXO-HC536R-1 (U6) quartz
crystal oscillator. This oscillator allows the AD5934 to excite the
conductivity cell with a frequency of 2 kHz, which is well suited
for conductivity measurements.

 

Naturally I tried the measurements with the output clock but the output frequency is not good in this case either.

 

What else could I do to correct the output frrequency, or what should I check? I have checked the following things:

-clock setting in the control register OK

-start frequency code OK

-increment frequency code OK

-start frequency and increment frequency code write to the registers OK 

 

Thanks for the help!

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