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TLC5941 Mode question .

Tom Cjin
Prodigy 190 points
Other Parts Discussed in Thread: TLC5941

Hi ,

 TLC5941 has mode pin, 

"Input mode-change pin. When MODE = GND, the device is in GS mode. When MODE = VCC, the device is in DC mode.".

We has a question about this , does the chip can use only one mode at a time?

We want use different current on different Out Channel , that is , We do configure by Mode DC to configure each Channel max current (Channels have different number of LEDs in parallel) , after that , we use GS mode to change LED brightless(RGB color).

 

Is that possible ?

Thank you.

  • 0
    TI__Genius 13700 points

    Hello Tom,

     

    The mode pin sets the operation for the whole device. Individual pin mode configuration is not possible on this device.

     

    The IREF pin is used to set the maximum channel current which could be configured to set the absolute max channel current which must be withing the current limits defined by the datasheet.

    With the max channel current set in this manner you can then adjust the GS values for each of the parallel configuraitons relative to the desired channel current. This means that you have the highest current/most parrallel LED channel define the max and then the channel current for all of the other strings is a GS value that is define relative to that maximum.

     

    Let me know if there are any questions.

     

    Ryan May

  • 0 in reply to Ryan May
    Prodigy 190 points

    Hi Ryan,

     thank you for your replay ,

     I noticed in the datasheet , that each channel has One Dc Resisger and One GS Register .  We just want to use them both, means

     Iout = Imax * DC/63 * Brightness% . 

    The Datasheet talked about both seperately , and not told us if they can use in the same time.

     thanks .

     

  • 0 in reply to Tom Cjin
    TI__Genius 13700 points

    Hello Tom,

     

    Looking through the datasheet I see what you are refering to.

     

    The DC (Dot Correction) Register is used to accomplish the relative scaling that I talked about between the different channels to let the GS values be used over their full range.

    So from what I can tell from the datasheet the Iout equation in you last post is how the device is intended to work. I apologize if I created any confusion.

     

    The process that you need to use is first discussed on Pg 16 the datasheet and the signal waveforms provide the information needed for programming the DC register when you have the MODE pin pulled high to set the channel max current as a fraction of the max current which is what you brought up in your last post. Then the MODE pin is pulled to ground and the GS or % brightness value can be loaded.

     

    Using this device will require loading values into both registers meaning you will need active control of the MODE pin since according to Pg 16 of the datasheet at the bottom the GS and DC registers contain random values that will need to be set by the user.

     

    Let me know if you have any questions.

     

    Ryan May