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TLC59116 different channel Load question.

Tom Cjin
Prodigy 190 points
Other Parts Discussed in Thread: TLC59116, TLC59116F

I have a disign as follow:

TLC59116  OUTx  ---->  LED

TLC59116  OUTx  ---->  LED10 -LED11                           (serials of leds)

TLC59116  OUTx  ---->  LED20 -LED21- LED22 ...          (serials of leds)

 

Means , the out channels each may have different number of LEDs , which all led are the same. and each channel total number leds will in the range of the max  voltage 17v

So, My question is , will each OUT channel have the same output current.

 

Thanks.

  • 0
    TI__Genius 14890 points

    Tom,

    The TLC59116 constant current is set through its  REXT resistor to ground.  Each channel will have the same current.  One thing to note is the power dissipation on each channel.  If the LED voltage is the same for each channel and each channel has a different number of LEDs, the excess voltage is extra power for the output.  For example, if channel 1 has a single LED with VF of 3V and the VLED is 10V, the voltage at the TLC59116 will be 10V - 3V = 7V.  The power will be I*V so with 100mA, the power on channel 1 will be 0.1A * 7V = 0.7W.  Each channel will be calculated the same way.  Alternatively, each channel can have its own VLED to minimize wasted power (but it does complicate the design).

    The TLC59116F is an open-drain version of the TLC59116. Each output will have its current set by the VLED, the VF and a resistor in series with the LED string.

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 190 points

    Hi Dick , Thanks for your replay ,

      I make some clears ,

        The first:

         TLC59116:

          OUTx <----( current ) --- LED ---- 5 V

          OUTx<-----( current ) --- LED --- LED ---- LED ---- 12V

           .....

          the chip always sense the current of into the chip , and make adjustment of the voltage on the out channel ,till the current equals the set through its REXT . No matter the  VLED's value .

          Right ?

     

         and , a second clear:

         If i use battery , the VLED may varies in the process ( become weak ) .  And then , the TLC59116 will lower its channel voltage , to make the current constant .

        Right?

     

     

        The scene of our design is we use same LED(means the same current ) , but we have to use diffent number ,because there need different brightness . So we have to make a clear of our design.

      

       And a third clear , if we use TLC59116F , then we just use different LED(means different current) , is this right?

     

        And  question , 

         1\\  if we use battery , so the TLC59116F will not be constant current ?  does it sense the current?   We use it drive full color LEDs . So if current varies , the color may not correct.

         2\\ If we disconsider the power loss , TLC59116 is better for us?

        Many thanks to you .

     

     

  • 0 in reply to Tom Cjin
    TI__Genius 14890 points

    Tom,

    First:  Right.  The remaining voltage will appear at the TLC59116.  The TLC59116 does not actually do any adjusting.  The voltage at the pin is a result of the VLED minus the drops on the LEDs.

    Second:  Right.  The TLC59116 will remain at a constant current no matter the VLED.  If VLED is too low, it may not be high enough to bias the LEDs properly.  In that case, the resulting current may droop, but the TLC59116 is still trying to maintain constant current.

    Third:  Right.  The TLC59116F current will vary with VLED.  The TLC59116 (constant current) is better for you than the TLC59116F in this case.

    Let me know if you have any more questions.

    Regards,

    Dick