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DAC8581 issues

Shaotong Zhang
Prodigy 140 points

Other Parts Discussed in Thread: DAC8581

I used a PIC24FJ128GA to interface with DAC8581, SPI protocol was setup a followed in ccs compiler:

   while(1)
   {    
      for(i=0;i<32767;i++)
         {output_low(PIN_A7);

          spi_write2(i);

         delay_ms(1);
         output_high(PIN_A7);
         }
   }

 

pin CLR was tied to DVDD, while CS is pin RA7, power supply and voltage reference was double checked to make sure everything is corrct. However,instead of getting the saw waveform im simply getting 0 and occasionally square wave(!) at Vout pin. I checked the SCLK pin and CS pin and make sured that there are more tha 16 clocks while cs is active low.

 

Could anyone tell me what is the problem?

  • 0
    TI__Mastermind 43915 points

    Hi Shatong Zhang,

    Double check you are using the correct clock phase polarity. You want to make sure you are writing on the rising edge of SCLK and having the input data change on the falling edge of SCLK. I would also look at your data on a scope to verify that you are meeting the timing specs shown in Figure 1 in the data sheet.

    Regards.

    Tony Calabria

  • 0 in reply to Tony Calabria
    Prodigy 140 points

    Thank you! I did set SPI's clock phase polarity to idle=> low level; active =>high level; transmitt occurs on transition from Idle to active clock state.

    and I did not finding any problem in timing diagram after I put a 1ms delay before putting cs back to high.
     
    However I did notice that when I connect the Vref pin to a high-precision voltage reference module, the output of the voltage reference dropped from 2.5V to 1.2V, and I was wondering whether or not it implies that there is something wrong with the chip?
     
    Shaotong

  • 0 in reply to Shaotong Zhang
    TI__Guru**** 182721 points

    Hi Shaotong,

    Applying a reference voltage to the DAC8581 should not cause it to droop from 2.5V to 1.2V if the chip is properly powered.  Please double check your connections.  Feel free to send along a schematic and a screen shot showing your SPI transfer and we'd be happy to look over them for you.