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OPT8241: Should these delay be equal or be irrelevent ?

user1473337
Prodigy 110 points
Part Number: OPT8241


When I will layout PCB, There are three delay time: 

(1) OPT9221  IO_MOD_REF --> OPT9221 ILLUM_MOD_FB;

(2)OPT8241  ILLUM_P/N --> OPT9221 ILLUM_MOD_FB;

(3) OPT9221 COMP_MOD_REF --> OPT9221 COMP_MOD_FB

Should  these delay be equal or be irrelevent ? any advice?

Thank you very much!

  • 0
    TI__Mastermind 49986 points
    Hello,

    We have received your query regarding the delay times of and between the devices OPT9221 and OPT8241 and will get back to you soon with the response.
  • 0 in reply to Praveen Aroul
    TI__Expert 3495 points
    1) OPT9221 IO_MOD_REF --> OPT9221 ILLUM_MOD_FB
    >> Keep these very close, IO_MOD_REF measure the OPT9221 I/O delay, so we don't want to add more trace delay.

    (2)OPT8241 ILLUM_P/N --> OPT9221 ILLUM_MOD_FB;
    >> Don't matter as much, as this delay is what the COMP_MOD_FB feature is compensating.

    (3) OPT9221 COMP_MOD_REF --> OPT9221 COMP_MOD_FB
    >> Trace length match these two.
  • 0 in reply to Larry Li
    Prodigy 110 points

    Hi Larry,

    I do not understand fully, I know modulation is done in OPT8241 and phase offset correction is done in OPT9221, How can OPT9221 use the these delays to calculate? can you give some figure to illustrate for me ? Thank you very much!

    addition: sbas703a--opt9221 datasheet.pdf give figure 15 to explain the delays, so  I think the delay from OPT8241 ILLUM_P/N --> OPT9221 ILLUM_MOD_FB is very critical.

  • 0 in reply to user1473337
    TI__Expert 3495 points
    Please note the XOR and comparator circuit; they are used to digitally compare actual illumination wave form with reference modulation wave form. Any difference will result in pulse code that can be used by OPT9221 to compensate for delay.