Output Frequency of CN0349

The maximum frequency you can get from the AD4934 is by writing 0xFF into all 3 registers.  With the 1 MHz MCLK frequency used  on the CN-0349 board, from the formula on page 13 of the datasheet you mentioned, the AD5934 would produce the maximum frequency of about 7812.5 Hz.
To make the board operate at 30 KHz it would be necessary to remove the U6 FXO-HC536R-1 1 MHz oscillator and replace it with a higher frequency one (for example, FXO-HC536R-16) or wire in the MCLK signal from some higher frequency external source such as lab generator, etc.
If the datasheet 16 MHz MCLK frequency is used, the maximum frequency the AD5934 would be able to generate is about 125 KHz.    

Thank you so much. I just dont understand how someone would NOT write something like that in the datasheet. Would have saved me days of work finding that out the hard way..

Anyways, thanks again.

Yes, unfortunately the documentation is not clear and there are quite a few behaviors in this chip family that are completely undocumented. Bumping into those in the middle of a project does create serious setbacks. Documentation limits marketplace acceptance of these otherwise rather unique chips.
Best of luck with the rest of your project, please do not hesitate to ask if you have any further questions. 

I had a look through the Circuit Note and the datasheet. It is true - it would have been a good idea to explicitly state the frequency range and resolution of the CN0349 given the 1 MHz master clock. It also looks like there's little to no mention of changing the frequency from a default value of 2Khz. The only mention in the note is "This oscillator allows the AD5934 to excite the conductivity cell with a frequency of 2 kHz, which is well suited for conductivity measurements." (Does the supplied GUI even allow the frequency to be changed?) Again, I absolutely agree that this should have been documented better in the circuit note.

But I don't see any ambiguity in the AD5934 datasheet - all formulas are expressed in terms of  MCLK frequency, with 16 MHz used as an example. The last paragraph on page 29 also explains when you might want to use a lower MCLK frequency.

I dug into the no-OS and Linux driver documentation as well. The only bare metal drivers for the AD5934 seem to be here: https://wiki.analog.com/resources/tools-software/uc-drivers/microchip/ad5933 . (note the title is actually for the AD5933.) This should be considered legacy code, any new development would be in the no-OS repository. It looks like the AD5933 IS supported in no-OS, and the exernal clock frequency is defined here:

https://github.com/analogdevicesinc/no-OS/blob/master/drivers/impedance-analyzer/ad5933/ad5933.h#L116

and can be changed through the driver functions:

https://github.com/analogdevicesinc/no-OS/blob/master/drivers/impedance-analyzer/ad5933/ad5933.c#L194

Similarly, the external clock must be defined for the Linux driver:

https://wiki.analog.com/resources/tools-software/linux-drivers/iio-impedance-analyzer/ad5933#example_platform_device_initialization

Once the MCLK is defined for these drivers, you should be able to set / read back the frequency properly.

Acknowledging this was frustrating for @muzot , hope this helps in the future.

-Mark

MarkThoren said:

 all formulas are expressed in terms of  MCLK frequency, with 16 MHz used as an example.

Indeed those formulas seem relatively straightforward, but evidently not to all users. 

MarkThoren said:

The last paragraph on page 29 also explains when you might want to use a lower MCLK frequency.

The last paragraph on page 29, however, is an example of a rather ambiguous text: it refers to 16.776 MHz as the "nominal clock frequency," while the rest of the datasheet text uses 16 MHz as typical MCLK frequency. 16.776 MHz is the frequency of the AD5933 internal oscillator, so this is the frequency that cannot "be scaled down" as it is not under user's control. When this passage is found in the AD5934 datasheet it is even more confusing as the AD5934 does not have the internal oscillator. And nowhere in the AD5934 datasheet it says that on power up the chip is set to operate from the clock coming from this non-existent internal oscillator. Naturally, this clock is not coming and the chip appears dead. So it is user's responsibility to enable it's operation from the external clock by programmatically setting bit D3 in the control register, but how one would know?