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DAC82001: There are strange jumps in the output signal of DAC

s s
Prodigy 20 points
Part Number: DAC82001

Tool/software:

We are using DAC82001 for high accurcy voltage output. but we found strange jumps when testing.

Out design parameters are following:

Vref = 1.024V

DAC output data from 0 to 255, then 255 to 0, total 256 steps.each step 40ms.

Can someone give any suggestion about this observation? I guess it is related with the switch from  such as b'011111 to b'100000， but have no evidence.

Thanks.

  • 0
    TI__Mastermind 33038 points

    Hi SS, 

    Are you able to isolate which codes these jumps are happening at? It's a bit hard to tell from your figure. That would help us confirm if the jump is happening at transition code like you pointed out, or some other cause. It looks repeated at consistent intervals which could be a result of a large switching transition, or it could mean there is some repeated bug in your code when these jumps are happening. 

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    Prodigy 20 points

    Hi, Katlynne

    Thanks advance for your help.

    In our observation, when we set following DAC datas, the output have unexpected jump:

    0x801F<->0x8020,

    0x805F<->0x8060,

    0x809F<->0x80A0,

    0x80DF<->0x80E0

    when from low to high, the output is unexpected drop,

    when from high to low, the output is unexpected rise.  

    BR,

    Steven

  • 0 in reply to s s
    TI__Guru 53563 points

    Hi SS,

    As these are major carry codes, I think we should confirm if we have some digital issue here.  My concern is that the SPI timing is being violated here and maybe we have some data getting shifted on the wrong clock edge.  Can you please capture an oscilloscope image of the the SPI frame showing the edge relationships?

  • 0 in reply to Paul_Frost
    Prodigy 20 points

    Hi, Paul

    Many thanks for your information.

    You means we should capture a snapshot by oscilloscope to check the timing between SPI SCK and MOSI when the issue happened? 

    Actually, we had previously suspected an issue with SPI by reducing its clock from 32MHz to 3.2MHz, but the problem still persists.

    and we checked spi timing by oscilloscope and it seems okay.    Cry

     

    BR,

    Steven

  • 0 in reply to Paul_Frost
    Prodigy 20 points

    Hi, Paul

    These abnormal outputs are very regular, appearing at these points every time. Guess may not a timing issue?

    BR,

    Steven