AD5930/AD5932

Hi! For a project I need to generate a 18kHz to 70kHz signal using either the AD5930/AD5932 in sweep mode. 

However when programming either of the two with SPI (yes even the AD5932). It seems to show a burst profile (I can add pictures later, if necessary). The frequency is not equal to the start frequency (the signal range is about 1kHz to 10 kHz) and it starts midway; at around 5kHz.

I can however change wether the output is a sine or triangle, thus I do not believe the SPI is not transferring at all, seeing as it still processes this signal. Changing bit D7 (burst) has no effect on the AD5930. The AD5932 doesn't have the burst capability and still shows a burst profile with the same registers!

The following are my register initializations for the AD5930 (the only thing different in the AD5932 is the control register)

  • Control register: 0x0F1F (sine wave, saw sweep and burst disabled)
  • Fstart LSB = 0xC798 (start frequency of 18kHz with a 50 MHz clock)
  • Fstart MSB= 0xD001 (start frequency of 18kHz with a 50 MHz clock)
  • Frequency increment LSB: 0x229F (2kHz increments)
  • Frequency increment MSB: 0x3000 (2kHz increments)
  • Number of increments: 26 so: 0x101A
  • Interval register: 0x400A (no multiplier, it outputs each frequency for 10 periods)

I left the burst register empty, considering I am not using it. Both the AD5932 and AD5930 show the exact same result. 

I also already checked the SPI signal on a scope, which I decoded and it is transferring fine. One weird thing is that when in software I close the SPI, both the chips result in a output of midscale? However I cannot figure out why this is.

Thanks in advance and if anyone needs more information, I'll give it.

Best regards, Jennifer.