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ADS127L18EVM-PDK: Resistor between output and FPGA

Shinichi Inoue
Guru 21951 points
Part Number: ADS127L18EVM-PDK
Other Parts Discussed in Thread: ADS127L18

Tool/software:

Dear Specialists,

My customer is referring ADS128L18EVM-PDK and has a question.

I would be grateful if you could advise.

----

I am currently designing using the ADS127L18EVM circuit as a reference.

(1) In the ADS127L18 EVM, Figure 2-3 below shows the 10Ω resistors R19 to R39.
What are the purposes of the 100kΩ resistors R9 to R18, R184 to R193, and R198?

(2) In our case, the output of the ADS127L18 will be connected directly to the FPGA.

At this time, I'm connecting directly to the FPGA, so I understand that removing the 10Ω and 100kΩ resistors is not a problem.

Is this understanding correct?

---

i appreciate your great help in advance.

Best regards,

Shinichi

  • +1
    TI__Mastermind 48160 points

    Hello Shinichi,

    Yes, you can omit the 100kOhm resistors.  These were added to the evaluation board so you could connect an external MCU/FPGA and not connect all digital IO lines.  In the customer's board, they can remove these resistors.

    Yes, you can also omit the 10Ohm resistors if the ADC and FPGA are close to each other on the same board.  The 10Ohm series resistors are placeholders in case there is excessive ringing on the digital lines due to signal overshoot or undershoot, especially when using an external MCU/FPGA board with jumpers.  A good board layout with the ADC 'close' to the FPGA, normally less than 10cm, will not require series resistors.  

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Guru 21951 points

    Hi Keith,

    Thank you for your reply.

    I shared your answer with the customer.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi