ad5781 could not output square wave above 10 khz

ad5781 circuit.rarU10 is AD8675

Hi xxu ,

  is currently taking a look at this query. Thanks for your patience.

Best Regards,

Den

thank you for your reply.provide detailed operations of software:

void ad5781_spi_write(u8 addr, u32 val)

{

    set_ldac(low);

    set_sync(low);

    ...//write register

    set_sync(high);

    set_ldac(high);

}

void timer_callback()//

{

   u32 val;

   static u32 reversal_flg = 0;

    val = reversal_flg ? 0x8F<<12:0x7F<<12;

    ad5781_spi_write(0x1,val);

    reversal_flg = !reversal_flg;

}

void init_ad5781()

{

      set_reset(low); delay();set_reset(high); 

      set_clr(high); set_ldac(high);set_sync(high);

       delay();

      ad5781_spi_write(0x2,0x12)

}

Hi xxu 

The maximum update rate of the DAC can be achieved if we have an optimized timing for the spi write. You could refer to the approach on this thread (+) what is the maximum analog output frequency of AD5791? - Q&A - Precision DACs - EngineerZone

The interface time (spi communication) and settling time defines for the update rate. See this thread as well (+) Precision DAC sample rate - Q&A - Precision DACs - EngineerZone (analog.com)

Purely looking at the AD5781 specs, we should be able to achieve 1Msps at the output. That is enough for a 500kHz square wave.

I'm not sure how timer works in your program, if you could give a capture of the spi waveform (ldac included) I could give some guidance on where we can improve. 

Best regards,

Ian