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OPT3101: Peak LED driving current and some clarification from the datasheet

Mehdi Aas
Prodigy 20 points
Part Number: OPT3101

Dear Sir/Madam,

I have a few question regarding the datasheet and the sample design:

1- in page 105 from datasheet how do you come up with the equation 11. What is the number 30 in the numerator and denominator of this equation? 30/(30+C_PD)?

2- For the sample design using OSRAM SFH4550 LED mentioned in page 103 of the datasheet, in order to have 64mW radiant power in the FOV, we need to have 7.4W/sr intensity from the LED. This is only possible if the peak driving current of the LED be around 670mA. So my question is: Is the maximum rating for I_DRV=173.6mA at page 6 related to an average driving current or it is the maximum available peak current from the chip in pulsed condition? If it is the pulsed peak current then do we need an external power supply for LED?

3- Is there any limitations for the rise/fall time of the LED?

4- in page 18, equation 4, how do you derive the second equality? What do you mean by BW signal measurement bandwidth?

Thank you in advance.

Kind regards,

Mehdi

  • 0
    TI__Mastermind 25895 points

    Hi Mehdi,

    I will get back here by early next week.

    Best,

    Alex

  • 0 in reply to Alex Bhandari-Young
    Prodigy 20 points
    Hi Alex,

    Thank you very much. I will be waiting for your feedback.

    Bests,
    Mehdi
  • 0 in reply to Mehdi Aas
    TI__Mastermind 25895 points
    Hi Mehdi,

    Sorry about not posting back here. The thread got marked resolved so it dropped off my list, but I didn't realize I had not posted the answer.

    1) The 30 in the equation is internal capacitance
    2) This calculation does not look correct. Checking the datasheet of the SFH4550 the radiant flux at 100mA is 70mW. If you see page 105 in datasheet "The SFH4550 produces 70 mW of optical power for a current of 100 mA. From this, the required illumination current can be calculated as 91.5 mA". Since the OPT3101 duty cycles the 173mA is the amplitude of the square wave.
    3) For this please refer to the system design doc posted online in the Illuminator Selection section.
    4) BW refers to the ave_frames + 1 you should see this in the next part of the equation in this part of the datasheet.

    Best,

    Alex