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Application for dimming white LEDs on multiple channels

Todd Larson
Prodigy 10 points
Other Parts Discussed in Thread: TLC5940, TLC59116, TLC5947, TLC5971

I have an application for dimming white LEDs on multiple channels.  I have tried using the TLC5940 with 16 channels with dot correction and grayscale PWM with some success.  Generating the GS clock is messy at best.  If a 25MHz internal oscillator was provided for the GS clock, this would be a nearly perfect device for my application.  The TLC59116 with its internal oscillator is a step in the right direction, but loss of dot correction of individual channels and loss of PWM resolution (8 bit instead of 12 bit) makes it less ideal.  The TLC5947 and TLC5971 are ruled out because any PWM frequencies below a few kHz are unacceptable in my application.  The following would be my dream device:

 

12 or 16 Channels Individually Dimmable

25MHz Internal Oscillator for GS Clock (PWM)

10 or 12 bit Grayscale PWM Control (PWM frequency is still plenty fast)

4 or 6 bit Dot Correction of Individual Channels

Drive Capability (Constant-Current Sink) 0 mA to 120 mA (VCC > 3.6 V)

LED Power Supply Voltage up to 17 V

VCC = 3 V to 5.5 V

Serial Data Interface or I2C

 

Please let TI know if you have an application that would work better with such a device.

  • 0
    Intellectual 970 points

    Please let me converse with you my  good friend.

    The  TLC5940 is a linear diming LED Driver.

    If this application is for LED-Backlight LCD TV then i beg you not to use it.

    The only truly efficient  way to drive LEDs in LED TV is to use either:-

    1. A  Dimmable LLC resonant LED Driver switching directly off the  PFC Bus

    2. A  dimmable dual-phase, interleaved flyback LED Driver switching directly off the DC Bus

     

    Any other technique involves cascading too many  converters and is more  inefficient.

    Linear LED Drivers are too inefficient full-stop.

     

    The idea of being able  to individually dim every square inch of an LED-Backlit TV on a frame-by-frame basis is a hoax.

    -it requires too many  LED current regulation stages and is too inefficient.

    i beg you to use single stage LED Driver , dimmable solutions....that is a single stage switching from the PFC  Bus.

    Use high voltage LED strings as you can......it means less switching stages needed.