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AD5932 MSBOUT behavior

Question asked by Dr_Phil on Aug 30, 2017
Latest reply on Sep 20, 2017 by musach

I'm trying to use the AD5932 to generate a 12 pulse waveform. I'm using a 16 MHz oscillator and have programmed TINT = 4 (D15 to D11 = 01000), NINCR = 2 with auto-incrementing enabled. FSTART and DELTAF correspond to 420 kHz and 25 kHz, respectively. I'm interested in a square wave output so I'm looking at MSBOUT.

 

The problem is that MSBOUT jumps between two or three frequencies (~15 kHz apart) within each frequency interval. The plot below shows the results from 3 separate sweeps (they're basically coincident):

 

 

Basically, I get the same (wrong) sweep each and every time, even if I reprogram the chip between sweeps. I've tried different MCLK sources and frequencies and, in every case, see the same intra-interval frequency hopping from sweep to sweep. I see the same thing whether the DAC is enabled or not. I've also tried a second AD5932 that yields the same result.

 

Any help would be most appreciated. Thanks in advance!

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