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low frequency(less than 100 Hz) performance of DAC 5652

walter maina
Prodigy 50 points
Other Parts Discussed in Thread: DAC5652

Hi, let me begin by thanking texas instruments for providing me with free samples of DAC 5652. I was able to make a circuit for it as described in DAC 5652/72/62 users guide, with an intention of using it ina direct digital frequency synthesizer. the specifications are as follows clock frequency of 50MHz , DAC in dual bus mode and the analog output is in single ended configuration. When I try to generate frequency that is less than 100Hz for a sinewave,the sinewave is present but it appears  to have another frequency (square wave) inside the shape of the sinewave just like in amplitude modulation. the oscilloscope only picks up the frequency of the square wave (6.25KHz)but not that of the required sinewave. what could be the problem because at 100KHz Iam able to observe a good sinewave, without a square wave inside it.

I lookforward to hearing from you

Thank you in advance

  • 0
    TI__Expert 5820 points

    Hello

    Are you using DAC5652 EVM? The transformers T1 & T2 on the EVM are "T1-1T-KK81", with a passband of 80 kHz to 200 MHz which would explain why you see the desired output at 100 kHz but not at 100 Hz. See section 2.2.3.2 on page 15 of user guide to bypass the transformer and probe differential output of DAC.

    Sincere Regards

  • 0 in reply to Hamza Fraz
    Prodigy 50 points

    Hello

    Iam not using the DAC 5652 exactly, however I used the schematics provided in chapter four of the DAC 5672/62/52 user guide to make a circuit on printed circuit board. The only difference was at the output where instead of the transformer, I used the single-ended configuration described on page 17 of the DAC 5652A datasheet (SLAS535A-SEPTEMBER 2007-REVISED MAY 2009).

    Thanks for the initial reply, please respond to this one also.

  • 0 in reply to Hamza Fraz
    Prodigy 50 points

     Hello Hamza, thank you for the reply you gave me, as I tried to check the recommendations you had made, I came across the problem with my DAC circuit; I had grounded the fourth bit( counting from LSB). Please ignore the post Ihad made earlier today describing the type of circuit I was using.

    Thanks alot