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TPS8802: Photodiode and Blue LED Spectral Sensitivity Difference

ilgin sarican
Prodigy 215 points
Part Number: TPS8802

Hi,

I want to use TPS8802 Smoke Alarm AFE.

In Evaluation module for TPS8802 datasheet , the Spectral Sensitivity range of photodiode(partnumber:SFH 213) is between 750 ... 1100nm and  the Spectral Sensitivity range of blue LED is between 420-520(approximately).

How can photodiode detect wavelenght of blue LED?

Thanks.

  • 0
    TI__Intellectual 1965 points

    Hi,

    Thanks for your question.

    The TPS8802EVM uses a SFH 213 photodiode, which has a spectral sensitivity range of 400nm to 1100nm. This is not to be confused with the SFH 213 FA, which has a spectral sensitivity range of 750nm to 1100nm. The SFH 213 FA has an IR filter on it which makes it look dark. The SFH 213 has a transparent package.

    The included LEDs and photodiode on the TPS8802EVM are good for testing the electrical performance of the TPS8802 LED drivers and photo-amplifier. The included LEDs and photodiode will not work for detecting smoke. It is recommended to connect the TPS8802EVM to an optical chamber if you have one available.

    I hope that answered your question. Let me know if you have any further questions.

    Best,

    Grant

  • 0 in reply to Grant Falkenburg
    Prodigy 215 points

    Dear Grant,

    Thanks for your return.

    Could you tell me why the included LEDs and photodiode will not work for detecting smoke?

     I examined a few smoke detectors, there were IR LED and photodiode (similar to SFH 213 and SFH 4556) in them.

    Is there any special reason not to work for detection smoke?

    Actually, I have chamber and want to use SFH 213, SFH 4556 and LTL1CHTBK4 with my own chamber and on my PCB.

    Is it because the photodiodes are not working and there is no chamber on the demo board?

  • 0 in reply to ilgin sarican
    TI__Intellectual 1965 points

    Hi,

    You are correct. The LEDs and photodiodes on the TPS8802EVM are standard optical components that can be used to detect smoke. However, when these components are used on the EVM, ambient light will saturate the photo amplifier and prevent smoke from being measurable. This is why I recommend connecting an optical chamber (LED, photodiode, light shield) to the EVM. The optical chamber also aligns the optical components to optimally detect smoke. The EVM could work for detecting smoke if there is no ambient light in the room and the direct optical path from LED to photodiode is blocked.

    Let me know if you have any further questions.

    Best,

    Grant

  • 0 in reply to Grant Falkenburg
    Prodigy 215 points

    Dear Grant,

    Thanks for your return.

    I have one more question.

    Could you share product number of CO sensor in TPS8802EVM User's Guide?

    I research many CO sensot but they are very big.

    The sensor that shown in User's Guide is as small as I wanted.

    Have a good day.

  • 0 in reply to ilgin sarican
    TI__Intellectual 1965 points

    Hi,

    The CO sensor used in the TPS8802EVM User's Guide is the Figaro TGS5141.

    Let me know if you have any other questions.

    Best,

    Grant

  • 0 in reply to Grant Falkenburg
    Prodigy 215 points

    Thank you so much.