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OPT3002: Different sensor values in conversion mode Single-shot and Continuous

Ulrich Pahl1
Prodigy 190 points
Part Number: OPT3002
Other Parts Discussed in Thread: MSP430FR5728

Hello,

we have an application were we use the OPT3002 sensor to measure the irradiance of LEDs.
The OPT3002 is connected to a MSP430FR5728. The OPT3002 is configured as follows:

  • End of Conversion mode
  • Automatic Full-scale setting mode

and we have varied the following settings:

  • Conversion mode:
    1. Single Shot mode
    2. Continuous mode
  • Conversion time:
    1. 100 ms
    2. 800 ms

The following figures show the differences in the sensor value depending on these variations.

Measurement conditions:

  • The LED is driven by constant current source.
  • We have measured the irradiance at the following LED currents: 50 mA, 100 mA, 200 mA, 300mA and 500 mA.
  • The measuremnt is done more than 10 times with an reproducibility of +/- 5%.
  • The value of the irradiance is given in digits.

Diagram 1: Irradiance measured in single shot mode - conversion time: 100 ms and 800 ms

Diagram 2: Irradiance measured in continuous mode - conversion time: 100 ms and 800 ms

The sensor value measured in continuous mode at LED currents of 50 mA and 100 mA is about twice the sensor value measured in single shot mode.
At LED currents above 100 mA both conversion mode deliver nearly the same sensor value.

So we are wondering about these strange results and we are looking for an explanation.

Best regards

Ulrich