• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 46 subscribers
  • Views 165 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.

ADS127L11: Why is 3ohm resistor needed between external capacitor and AVDD1 terminal?

Kazuya Nakai59
Guru 20780 points
Part Number: ADS127L11

Hello guys,

One of my customers is considering using ADS127L11 for their new products.

At this moment, they have the following questions.
Could you please give me your reply?

Q1.
Why is 3ohm resistor needed between external capacitor and AVDD1 terminal?
Does it work as a CR filter? if so they think the externa capacitor should be placed between the resistor and AVDD1 terminal.
Is their thought wrong?

Q2.
How much is the allowance of this 3ohm resistor?
Is it OK to place 3.3ohm, 2.2ohm or 4.7ohm?

Your reply would be much appreciated.

Best regards,
Kazuya.

  • 0
    TI__Mastermind 40870 points

    Hello Kazuya,

    Q1.  The 3ohm resistor needs to be placed directly between the AVDD1 bypass capacitor and the AVDD1 pin of the ADS127L11.  I understand that this looks strange, but there is internal capacitance inside the ADS127L11, and this external series resistor helps to further filter the supply.  If the customer prefers not to include this resistor, the device will still work well but the offset voltage will increase without this resistor.

    Q2.  The external resistor can be anywhere from 2Ohm up to 4Ohm.

    Regards,
    Keith Nicholas
    Precision ADC Applications