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ADS8568: Power supplies and daisy chain operation

PieterT
Intellectual 610 points
Part Number: ADS8568

Tool/software:

Good day everyone,

I plan to use 3 ADS8568 adcs connected in a daisy chain configuration with a series output, configured via hardware mode and each with their own internal clock.

The input voltage from the driving circuitry will most likely be +- 5V or maybe +-10V.

1) From the recommended operating conditions I assume this is what the ADC should be driven at irrespective of the input voltage (as long as HVDD and HVSS are larger/lower respectively than the input voltage)?

As far as I can tell these supplies are irrespective of the input voltage (as long as HVDD and HVSS are larger/lower respectively than the input voltage) and if so, I will drive HVDD = +15V, HVSS = -15V, AVDD = +5V and DVDD = 3.3V unless there is some reason I shouldn't. 

2) As I am driving 3 ADCs do these would it be recommended to drive each ADC with its own set of power supplies or should they be all connected to the same set?

3) Is there any issue in having them operate on their own internal clocks or should they be driven by a single external clock with length matched traces to each?

4) Should they use the same reference or is each operating on their own internal reference fine?

4.a) I assume to ensure that the voltage conversion of the 3 ADCs should be done with respect to the same reference?

Thanks in advance for any help.

  • +1
    TI__Intellectual 1740 points

    Hello Pieter,

    Thank you for your question

     

    1. Correct, HVDD and HVSS is recommended to be within the ranges in the "7.3 Recommended Operating Conditions" table, as long as there is the 0.3V headroom/footroom specified in the "7.1 Absolute Maximum Ratings" in reference to the analog input. +/- 15V would work great with these devices since the input is limited to max +/-12V (3V VREF operation). All the other supplies meet the recommended/typical specs as well so it should work well. The only thing to note is to ensure your digital communication is at the same level of DVDD. 

     

    1. As long as the supply can provide the current consumption of the 3 ADCs simultaneously being used and section "11 Power Supply Recommendations" is followed per device it should be ok to supply all ADCs the same power supply set. 

     

    1. Using the internal or external converting clock would work equally well

     

    1. The device does have an internal low-drift 2.5V reference that can be adjusted via an internal DAC and it is directly tied to the input voltage range, so using the internal references in each device should work well.
      1. There will probably be some gain error discrepancies between the ADCs but step can be taken to calibrate the gain and offset with the internal reference.
      2. Having an external reference is always an option too to avoid calibration. I would recommend the reference block used can drive the 3 ADCs and maintain a stable low noise value. The Typical Applications section shows a sample circuit for this.

     Best regards, 

    Yolanda

  • 0 in reply to Yolanda Gonzalez
    Intellectual 610 points

    Thank you Yolanda, highly appreciate the information