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TLC 5940: Why LED intensity decrease when generate BLANK signal every 4096 pulses?

Pedro Ortiz
Prodigy 20 points

Hi, we are using three TLC 5940 connected to one PIC18F4620 that generate the control signals.

The problem appears when we activate the BLANK signal every 4096 pulses, the LED intensity result very poor.
When we use BLANK signal every 256 pulses, the LED brightness increase well. However, the interruptions the microprocesor generates in order to activate the BLANK signal every 256 pulses, produce an undesirable big delay in all the whole lights secuency.

Our question is: Why the LED intensity decrease when we generate BLANK signal every 4096 pulses?.

thanks a lot, in advance.

  • 0
    TI__Guru 65200 points

    Hello Pedro,

    What did you program in the gray-scale (GS) and the dot correction (DC) registers?

    Whenever BLANK is toggled, the GS counter is reset and a GS cycle starts from the beginning. Therefore the LEDs will be on for a longer portion of one GS cycle when the cycle is just 256 pulses long compared to 4096 pulses. When you want to use 4096 pulses for the GS cycle, you have to increase the GS register values to get the LEDs on for a longer portion of the 4096 pulses.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 20 points

    Hello Briggite,

    Thanks for your support!

    We finally chosse the way to generate _blank pulse from PWM signal from the PIC 18 feature.

    It works. We already done.

    Thanks!

    Until the next.

    Peter