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DAC8760: what is DIDD AIDD AISS in datasheet

Albert Chen76
Intellectual 270 points
Part Number: DAC8760

I would like to estimate current consumption for DAC8760 when full load.

But there are not  clear description of DIDD AIDD and AISS in datasheet.

I'm not sure how to or do i have calculate DIDD AIDD which is in the table below.

  • 0
    TI__Expert 5820 points
    Hi Albert,

    These are the current requirements of AVDD, AVSS, and DVDD respectively. The device needs some current for it's internal circuitry. To estimate the total current you can simply add these together with the loop current (20mA). For example in current mode, 3mA+0.6mA+1mA+20mA = 24.6mA. Let me know if you have further questions.

    Thanks,
    Garrett
  • 0 in reply to Garrett Satterfield
    Intellectual 270 points

    Here's a case for my design:

    +/-15V for AVDD & AVSS    +5V from external regulator for DVDD

    the spec. of analog output for my product will be +/-10V output and 24mA current output.

    in current mode:

    in worse case, the total power is +15V*24mA+|-15V|*2.6mA+5V*1mA+15V*3mA=total power

    1. should i have to add AVSS*AISS in total power calculation?

    2. when max current ouput(24mA), the worse case voltage would be 15V?

    3. is the formula correct for current mode?

    in voltage mode:

    +15V*4.6A+|-15V|*2.6mA+5V*1mA=total power

    1. is the formula correct for voltage mode?

  • 0 in reply to Albert Chen76
    TI__Expert 5820 points

    Hi Albert, 

    For current mode:

    1. Yes, AISS should be included in the power dissipation.

    2. I am not sure I understand what you mean by worst case voltage. Can you clarify?

    3. Yes it is correct for total power dissipation. In these AO designs we typically are only concerned about on-chip power dissipation. You can subtract out Iout^2*Rload from your formula above.

    For voltage mode:

    1. This will estimate the on-chip power dissipation. There will be some power dissipation at the load, Vout^2/Rload. Again, on-chip power dissipation is the concern as the load power dissipation occurs remotely. The short-circuit current of Vout is ~30mA. So the worst case total power dissipation will be approximately 15V*(30mA+4.6mA+2.6mA)+5V*1mA.

    Thanks,

    Garrett

  • 0 in reply to Garrett Satterfield
    Intellectual 270 points

    Hi Garrett

     

    2.

    I was confused about Iout current will be supplied by which rail or what voltage when in current mode.

    for example.

    if Iout current from AVDD 15V rail, i have to deliver 15V*24mA=360mW at least from 15V DC/DC to DAC for maximum current output

    or

    DAC8760 maximum voltage output is 11V even deliver 15V to AVDD, so i have to deliver 11V*24mA =264mW at least, 264mW/15V=17.6mA from 15V regulator for DAC8760 current output 

     11V*24mA =264mW  will be worse case or 15V*24mA=360mW

  • 0 in reply to Albert Chen76
    TI__Expert 5820 points
    Hi Albert,

    The maximum voltage output of 11V is only for VOUT, but it seems like your question is about IOUT. The voltage of the current output can approach AVDD to drive the current through the load. Basically, the device drops the "extra" voltage between AVDD and the voltage required to drive the load. So if AVDD=15V, the power dissipation will be 15V*24mA=360mW.

    Does that answer your question?

    Thanks,
    Garrett