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Compiler/AFE4403EVM: LED driving current drift

Rex Hsieh
Prodigy 160 points
Part Number: AFE4403EVM

Tool/software: TI C/C++ Compiler

Hi Sir,

I was trying to use AFE4403 EVM for some static photoelectric measurements, checking light intensities through solvents with different concentrations.

The LED driving current will be drifted every time(around 20~30 secs) when the Tx is switched on.  

The current drift is quite big(8mA->2mA)(with the default setting) in the first second, and it is stable over time.

I measured an experiment that I put EVM with SpO2 sensor in the darkroom. Then I switched on the Tx and captured the result that the phenomenon had happened as well.

I just wonder if possible to reduce/remove these current drifts.

Best Regards, 

Rex

  • 0
    Prodigy 160 points

    Attach the result.

  • 0 in reply to Rex Hsieh
    TI__Mastermind 49176 points

    Hello Rex,

    Can you please share your AFE register configuration?

    Which optical sensor shipped with the evaluation module did you use for your tests?

    How did you measure the current drift (8mA to 2mA)?

  • 0 in reply to Praveen Aroul
    Prodigy 160 points

    Hi Praveen,

    Thanks for the reply.

    Here comes the configuration as the attached file.

    I used the name of SFH7050 sensor for my tests and Agilent 34401A to measure the current for the test, but actually you can see through your eyes at the same time. (The LED's brightness) 

    Best Regards, 

    Rex6811.config.cfg

  • 0 in reply to Rex Hsieh
    Prodigy 160 points

    Hi Praveen,

    Please inform me once you have any updated news on the matter, thanks.

    Best Regards, 

    Rex

  • 0 in reply to Rex Hsieh
    TI__Mastermind 49176 points

    Hi Rex,

    Typically the settling behavior is due to the time take by the LED to reach thermal equilibrium.

    For the current drift of 8mA to 2mA, what was the programmed LED current?

    Also it is not clear how you measured the LED current using the Agilent multimeter since the LED will be pulsing.

  • 0 in reply to Praveen Aroul
    Prodigy 160 points

    Hi Praveen,

    The programmed LED current was 1.96078mA(20).

    It could change the timing of LED(full time) and close one of the LED(IR or R) to measure the average current;

    Without this setting, the forward current and the reserve current will be accumulated.

    It can be proved in the test results as well. 

    By the way, could you duplicate the phenomenon of the LED?

    Thanks.  

    Best regards,

    Rex

  • 0 in reply to Rex Hsieh
    TI__Mastermind 49176 points

    Hello Rex,

    The results that you showed earlier were with the LED turned on always but were they with the register configuration you had attached (25% duty cycle).

    I tried with the register configuration you had attached (evm default configuration) and I was not able to duplicate the phenomenon.

    How do you setup the sensor board? Have you placed it under a reflective surface?

    In my setup, I placed the sensor face down on the desk and left it untouched during the data capture.

  • 0 in reply to Praveen Aroul
    Prodigy 160 points

    Hi Praveen,

    The experiment that I measured was to put EVM with SpO2 sensor in the darkroom, and I switched on the Tx and captured the result that the phenomenon had happened.

    I also filmed a video and did an experiment that is easier to know.

    While I switched off the power down Tx button, the brightness of LED changes from bright to dark.

    Thanks.

    Best Regards, 

    Rex

  • 0 in reply to Rex Hsieh
    TI__Mastermind 49176 points

    Hello Rex,

    The wakeup time from powerdown TX typically is 1 sec. 

    Additionally as I mentioned before, the settling behavior is due to the time taken by the LED to reach thermal equilibrium.

  • 0 in reply to Praveen Aroul
    Prodigy 160 points

    Hi Praveen,

    Thanks for your help.

    good day.

    Best Regards, 

    Rex