AD4000 reference voltage and power consumption

Hello,

A couple of questions about AD4000 design:

It is a 1.8V device; however, the current consumption is not mentioned anywhere in the DS (or I am not looking hard enough). On page 6 of datasheet, power dissipation numbers are given for different sampling rates. Can one assume this to be power consumption (vs power dissipation) numbers also?

In user guide for AD4000 UG-1042 a buffered Vref ADA4807-1 is used. Can it be replaced with an alternate like ADR381? If not, what might be a good candidate for reference voltage?

Thanks

Parents
    •  Analog Employees 
    on Mar 18, 2021 1:27 PM

    Hi Mohi,

    Thanks for your queries. I'll address the current consumption question first:

    Current consumption per supply is unfortunately not spelled out in the data sheet but you can calculate them for VDD and VIO based on their power consumption specs and voltages. You can also take a look at the TPCs on page 15 which show supply current vs. temperature and power consumption vs. sample rate. Note that the current consumption will scale linearly with throughput (sample rate of the ADC), and VDD current is higher when High-Z Mode is enabled. Also, VDD is the only supply which draws more current when High-Z Mode is enabled, so the difference between 

    Just using the spec table power consumption items for now, we can estimate the following:

    VDD Current:

    • 2 MSPS, High-Z Disabled = (9.75mW)/(1.8V) = 5.4mA
    • **2 MSPS, High-Z Enabled = (9.75mW + (16mW - 14mW))/1.8V = 6.5mA

    VIO Current:

    • 2 MSPS = (0.5mW)/(1.8V) = 0.28mA

    **In this calculation, the term (16mW - 14mW) was taking the difference between the total power consumption with High-Z Mode enabled minus High-Z Mode disabled, since VDD is the only supply which draws more power when High-Z Mode is enabled. i.e. at 2 MSPS the VDD supply draws ~2mW more when High-Z Mode is enabled.

    Also as a reminder, all of these numbers scale linearly with throughput so if you sample at 1 MSPS instead of 2 MSPS, for example, these current and power numbers in general will be cut in half.

    I'll respond to your REF drive question in a separate comment.

    Thanks,

    Tyler

  • Hi Tyler,

    Your explanation is very through. Thanks for your help. A couple of questions.

    (16mW - 14mW) is taken from the power dissipation table. Correct?

    At the end of Table 1, "Energy per Conversion 7 nJ/sample" is stated. Would this energy draw includes total power consumption?

    In my case, I am inclined to use this number since sampling frequency will be less than 100Hz.

    Thanks again for your help.

Reply
  • Hi Tyler,

    Your explanation is very through. Thanks for your help. A couple of questions.

    (16mW - 14mW) is taken from the power dissipation table. Correct?

    At the end of Table 1, "Energy per Conversion 7 nJ/sample" is stated. Would this energy draw includes total power consumption?

    In my case, I am inclined to use this number since sampling frequency will be less than 100Hz.

    Thanks again for your help.

Children
    •  Analog Employees 
    on Mar 18, 2021 2:28 PM in reply to Mohi

    Hi Mohi,

    Yes, the 16mW and 14mW numbers are from the spec table.

    The "Energy per Conversion" spec is just a measure of the total energy consumed by the SAR ADC core per conversion, and I think this is a combination of VDD and REF current.

    Personally I think you should look at Figure 35 (Power Dissipation vs. Throughput TPC) instead of the Energy per Conversion spec. That TPC shows typical power consumptions down to 10SPS for VDD, VIO, REF. You can see that the power consumption does start to "flatten out" at low sample rates because at that point the standby current/power consumption is a large portion of the total current/power consumption.

    The numbers in that table are obviously in mW, so you'll have to scale them down by the appropriate voltages for current, as described in the previous comments.

  • Thanks, Tyler. Appreciate your comments.