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OPT3001-Q1: Conversion time field in the register maps

Naoto Nakazawa
Prodigy 10 points
Part Number: OPT3001-Q1
Other Parts Discussed in Thread: OPT3001

Tool/software:

We would like to confirm contents of "Conversion time field" in the register maps.
There are two questions for you.
In case of E[3:0]'s setting="0011b" and conversion time="100ms",  the datasheet is explained we can reduce the effective result resolution by two bits.

1.
Is there the register setting to reduce number of bits ?
If it is Yes, where is it in the register map ?

2.
Please tell me the positive/negative points of both cases(Reducing resolution two bits or not).


Best regards.

  • 0
    TI__Expert 4480 points

    Hello Naoto, 

    Operating in 100ms mode reduces the effective resolution for the full-scale ranges below and including 0101b for E[3:0]. 

    This means that for the lower lux level full-scale ranges (those below and including 0101b) the OPT3001 will report 0's for the LSB effected. 

    This is because the shorter conversion time does not filter out as much noise so these bits would not be meaningful. 

    The advantage is faster and more frequent measurement.

    The drawback is the lowered resolution. Meaning device cannot detect as small of changes in light exposure while in the effected ranges. 

    The results register does not change, the relevant LSB just always report 0 when in one of those ranges below and including 0101b

    Thank you, 

    Joseph Scherphorn

  • 0 in reply to Joseph Scherphorn
    Prodigy 10 points

    Thank you for your reply.
    We have an additional question.

    In case of E[3:0]'s setting="0011b"(Full scale range=327.60lux) and conversion time="100ms",
    If OPT3001 receives of 327.60lux, is it recognized as 327.36lux?
    Is it correct as following understanding?


    　FULL-SCALE RANGE: 327.60lux
    　LSB_SIZE: 0.08 lux per LSB
    　By reporting 0 for the affected LSB, bit value is changed "111111111100b" from "111111111111b".
    　bit value of "111111111100b" = DEC value of "4092". (The effective FULL-SCALE RANGE = 4092*0.08 = 327.36lux)

    Best regards.

  • 0 in reply to Naoto Nakazawa
    TI__Expert 4480 points

    Hello Naoto, 

    Yes, this is correct. With 100ms conversion time and device operating in the smaller full scale ranges device will output readings slightly below the stated full scale range setting due to the LSBs being stuck at zero in these cases.