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DLP2010EVM-LC: Question on setting RGB LED PWM

Part Number: DLP2010EVM-LC

 write rgb led pwm .docx

  • Please see attached document

  • Hi David, 

    Thank you very much for your question. I appreciate the detail you added to our post with the MS Word Document, however, in future posts, can you please post the text and images within the question box? This will allow other DLP users to learn from your question!

    As for your questions, here are my answers:

    Q1. Why is there a max current setting of 769mA and a min current setting of 101ma? 

    Answer: The maximum and minimum current are a function of both the LEDs and the LED driver (DLPA2005 and external circuitry). In order for the DLPA2005 and the LEDs to function properly, some minimum current needs to driver the LEDs. Due to the architecture of the DLPA2005 and external components, driving 0mA to an LED would make the switching timeAlso, the LEDs are only able to handle a curtain maximum current and the driver circuitry can only supply a curtain amount of current as well. 

    Is there a specific current value you are trying to drive an LED that you are unable to?

    Q2. What are the PWM parameters? 

    Answer: The values sent to the system are not in mA. The PWM parameters are not transmitting the desire current to the system. The GUI tool takes the user’s specified current and translates this to a value that can be stored in a system register. The values you are seeing are the translated values sent to the system. 

    Please let me know if you have any other questions!

  • Below is the complete question with pictures:

    Currently we are trying to vary the LED current/PWM parameters to vary the luminous exposure of one or more LEDs which is needed for our application. We are doing the LED current modulation programmatically outside of the GUI. Could you please tell us how the system takes in a current value as input and translates it to a value that can be stored in the system register? Is there a formula etc. that we can use? Where can we find that information?

    ____________________________________

    I had a question (actually two) about setting LED currents.

    • Why is the max current setting 769 mA and the min current setting 101 mA?
    • What are the PWM parameters? If they are in mA, I would expect the transmit data on the Write RGB LED Current function in the following example to be:

     

    54 01 03 65 00 65 00

     

    Instead of:

     

    54 37 01 29 00 29 00

     

    • The transmitted data shown in the debug does not seem to correspond at all with the documentation or the values on the display screen. Red 0x0137 = 311; Green 0x0029 =49; Blue 0x0029 = 49. What am I missing here?

    Thanks

     

  • Hi David, 

    Thanks for the additional information. The register is 10 bits, so the values 0 through 1023 are allowed as inputs. The software however clips the values to protect the LEDs from being overdriven. 

    The formula for this translation can be found in the DLPA2005 datasheet. The formula is listed on page 16 under section 7.3.3. 

    Please let us know if you have additional questions!

    Thanks, 

    Brandon