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AD9833 - output failure

Question asked by ICM on Sep 25, 2014
Latest reply on Oct 17, 2014 by musach

Hello,

 

I am using DDS AD9833 to give frequency to full bridge inverter (48V).

DDS is drive in SPI.

Decoupling capacitors are not represented on picture.

DDS.PNG

flipflop.PNG

It works fine but after about 20 hours, output of DDS go to 0 during communication. The current on my inverter increases during this time.

I configure DDS in digital mode : TxDDS2(0x21,0x68);

I have looked communication during the problem : the value sended is right.

01+14 bits LSB, 01+14 bits MSB, 0x20 0x68

or

10+14 bits LSB, 10+14 bits MSB, 0x28 0x68


In yellow: clk

in green: mosi

in violet: Fsync

in red: current in my inverter

The current increase after first trame of data (14bis LSB) and decrease when I validate output.

spi5.PNG

 

Same thing but the current increase after second frame:

spi8.PNG


In yellow:comp

in green:vout

in violet:clk

in red: current in my inverter

Frequency vout is 149kHz before communication, 0 during communication, 149kHz after communication.

spi10.PNG


Do you have a idea to fix this problem?

Is it necessery to place buffers on communication line? Which kind of buffer?


I note that problem occurs more quickly when I place oscilloscope probes on clk or mosi.


 

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