• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 45 subscribers
  • Views 187 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS122U04: Common Power Supply source for Analog as well as Digital power supply input pins AVDD and DVDD

Milind Risbud
Prodigy 150 points
Part Number: ADS122U04

Hello,

I am designing a (dedicated) temperature sensing module (it shall be a a small stand-alone PCB), using ADS122U04.

The 5Vdc power supply for this PCB shall be applied via a pair of wires (+5vdc and Gnd) coming from another PCB located-

at a considerable distance. It is desired to keep the wires coming to this temperature sensing module PCB, as less as possible.

So, my question is that: Is it okay if I use just one pair of wires (+5vdc and Gnd) i.e. just a single power source to power 

the Analog (AVDD) as well as digital (DVDD) power supply input pins of ADS122U04. If so, will it be sufficient to use just

one 0.1uF decoupling capacitor for both these pins (i.e. AVDD and DVDD) shorted to each other (as they are the-

adjacent pins on the 16-Pin WQFN package) and still maintain a noise free and stable supply to AVDD?

or will more circuitry be needed for getting a stable supply voltage to AVDD pin?

Thank you, 

Regards,

Milind.

  • 0
    TI__Guru** 112705 points

    Hi Milind,

    Welcome to the E2E forum!  There are a number of unknowns that can affect operation.  For example, there is resistance in the wiring as well as inductance and capacitance that will directly impact the performance.  That said, your proposal will most likely work if the voltage remains stable and the current can be delivered when required.  You may want to add an additional larger value cap to be used as a bulk or charge reservoir near the supply pins as well.

    One additional item to note, I said this circuit needs to have a stable voltage and be able to deliver current.  You have not mentioned what type of temperature measurement will be made.  If the temperature is using an RTD where you will be exciting the RTD with current, then great care must be taken to make sure that when the IDACs are turned on that the voltage does not collapse to the point where the ADS122U04 can reset.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 150 points

    Hello Bob,
    Thank you very much for your reply and I apologize for delay from my side, in reverting back.
    The details that I missed mentioning earlier are that:
    a) I shall be using RTD PT100 in 2-wire configuration for measuring Engine Coolant temperature in heavy vehicles.
    b) I shall be using the WQFN (3mmx3mm) package of  ADS122U04.
    c) ADS122U04 and associated circuitry will be populated on a very small PCB (15mmx20mm) that shall be fitted in a very small enclosure and mounted besides the RTD sensor.
    d) This above mentioned module shall transmit the 24Bit results of AtoD conversions over long distance (for processing purpose) using UART interface of  ADS122U04.    

    As suggested by you, I will have to ensure that the 5Vdc supply voltage [that gets applied to this module via a pair of wires running over 5 meters (nearly 16 feet)]-
    remains stable and delivers the required current.
    I once again thank you for your valuable suggestions.

    Regards,
    Milind Risbud.