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TLC5925 control the Output-Current

Other Parts Discussed in Thread: TLC5925, TLC5927, TLC5926

I want to use five of the TLC5925 together.

My Problem:

I want, that all the Output-Channels of alle the 5 IC's make the same Output Curent, which I want to dynamicale change between 5 to 45 mA in oder to make the LED's more or less bright



So i want to control all of the 5 IC's(respectively the 5 R-Ext-Pins) from One Point to make sure all the Pins dynamically generate the same Output-Current for the LED's.


How can I realize that?


In which way the chip use the external Resistor according to adjust the Output Current?
is there a Voltage messaured, a Current?

so I could connect the R-EXT-Pin with a certain Voltage or a Current in Order to adjust the Output-Current?


Thank you for your time for answering.

  • Hello Jens,

    The external resistor is connected to a voltage source of 1.21V and the current through the resistor then defines the target output current. The target output current is 18 times bigger than the current through the external resistor.

    So to set the output current, you need a certain current flowing out of the REXT pin.

    Please be aware that at turn on, the register values are random, so the first thing before turning on the outputs is to program the registers.

    Best regards,
    Brigitte

  • The TLC5925 uses current mirror topology to set the current in the outputs.  Whatever current is on the REXT is multiplied to set the IOUT.  As such, you cannot tie multiple REXT pins to one point.

    Have you considered the TLC5926 or TLC5927?  Both devices have "current gain" which is a global brightness control.  By writing the Configuration Code, you can program the current to be below 10% of the programmed value.  Please review those datasheets to see if they can help with your application.

    Dick

     

  • Hello

     

    Thanks for your answers

     

    I'll take the suggested IC

     

    Jens