• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 32 subscribers
  • Views 60 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.

ONET1151L: Questions

Rohan Patel
Prodigy 20 points
Part Number: ONET1151L
Other Parts Discussed in Thread: ONET1151P, , ONET1101L

Tool/software:

Hi,

For ONET1151P and ONET1151L the datasheet states SDA as digital-input. Can you confirm if SDA here is bi-directional?

For ONET1151L, the following application report says that the ONET1151L MOD+/- pins are 500ohm differential back terminated for low-power designs and that an impedance matching circuit is critical.

https://www.ti.com/lit/an/slla335/slla335.pdf

The datasheet says MOD+/- are 25ohm single-ended back terminated (50 ohm differential back terminated). Is this the default setting? Setting ORADJ to 00 is the lowest-output termination which is the 25 ohm nominal but setting ORADJ to 11 results in the highest output resistance. Is this how to achieve the 500ohm differential back termination? The goal of all this is to determine if the impedance matching circuit is necessary. Ideally I would not want to add it so please comment if it is not needed or recommended when using the 25ohm single-ended back terminated setting.

Thank you!

  • +1
    TI__Mastermind 27227 points

    Hi Rohan,

    1. You are correct that SDA is bi-directional.  This is an error in out data sheet and I've noted it for our next revision.
    2. It looks like the application report you referenced is specific to ONET1101L, not ONET1151L.
    3. It's ambiguous from the data sheet, but I have seen that the POR register values for many of these ONET devices is 0x00.  I would expect that ORADJ default is 00.
    4. I'm looking into details how much ORADJ impacts back-termination and will get back to you this week.

    Thanks,

    Drew

  • 0 in reply to Drew Miller1
    Prodigy 20 points

    Thank you! Can you comment on if ONET1151L would need an impedance matching circuit? I would think not since the MOD+/- output can be 25ohm single-ended. 

    Thanks,

    Rohan

  • 0 in reply to Rohan Patel
    TI__Mastermind 27227 points

    Hi Rohan,

    This will depend on the laser impedance.  Note that calculations in SLLA335 revolve around laser impedance.

    Thanks,

    Drew