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TPS61020 for PWM dimming LED driver application

K.Yaita
Guru 29720 points
Other Parts Discussed in Thread: TPS61020
Hi Team,
 
Is it possible for TPS61020 to control LED current by PWM dimming?
If answer is yes, I'd like to know the solution.
 
I found the following schematic for LED driver application.
However, I think this solution can't control LED current and it seems just LED on/off function.
I also consider to use another device for this solution, however minimum input voltage(0.9V～) of TPS61020 is attractive.
 
 
Best Regards,
Yaita / Japan disty
  • 0
    Guru 29720 points
    Could you support me please?
    My customer's requirement is the following and I'd like to suggest TI solution.
    ---------------------------------------
    - input voltage: 1.8～3.0V
    - LED: Vf=2.7～3.3V (typ:2.85V)
    - LED current=200mA(MAX)
    - control interface: PWM only(not required I2C)
    ---------------------------------------
     
    Best Regards,
    Yaita
  • 0 in reply to K.Yaita
    TI__Guru**** 191445 points

    You might want to cross-post in the LED driver forum.  They may have a solution.

  • 0 in reply to JohnTucker
    Guru 29720 points
    John-san,
     
    Thank you for your comment.
    I asked LED driver forum about this solution, but unfortunately I heard most of LED drivers VIN_MIN is from 2.7 to 3.0V.
    If there is any solutions for your boost converter, please let me know.
     
    Best Regards,
    Yaita
  • 0 in reply to K.Yaita
    TI__Guru**** 191445 points

    I don't personally support, or have any specific knowledge of TPS61020.  Let's see if someone from that product line will respond.

  • 0 in reply to JohnTucker
    TI__Intellectual 1305 points

    Hi Yaita,

    This application can be used in LED driver.

    As you mentioned, when adding a PWM signal at the "flash lighting control", it only turns on/off the LED. When it turns on, the current is fixed. So this solution can not change the current directly. However, if the PWM signal changes its duty cycle and have enough frequency (for example higher than 100Hz), it can change the turn on time of LED, so that the brightness can be changed, which is equivalent to changing its current.

    BR

    Gene

  • 0 in reply to Gene Lu
    Guru 29720 points
    Hi Gene-san,
     
    I appreiciate for your support.
    I understood this application can be suggested for PWM dimming LED driver.
    Please let me know following 2 questions.
     
    1)
    I believe this application can't regulate LED current precisely because there is Vf variation even if LEDs are the same.
    Is my understanding correct?
    If ansewer is yes, I'd like to ask if my customer is acceptable for this.
     
    2)
    By the way, is it reasonable method to put resistor in series with Q1(Nch FET) to set the full scale value of LED current?
     
    Best Regards,
    Yaita
  • 0 in reply to K.Yaita
    TI__Intellectual 1305 points

    Hi Yaita,

    1) You're correct, this method can not regulate the current precisely.

    2) Remove the resistor R1 and R2, add a resistor in series with Q1 to ground and then connect the FB pin so that the   current can be controlled precisely. Just be careful of the resistor power consumption and value variation with temperature.

    BR

    Gene

  • 0 in reply to Gene Lu
    Guru 29720 points
    Hi Gene-san,
     
    I really appreciate for your suggestion.
    Does the following solution correct?
    If the answer is yes, I believe this is the best solution for my customer.
     
     
    Best Regards,
    Yaita
  • 0 in reply to K.Yaita
    TI__Intellectual 1305 points

    Hi Yaita,

    Please connect the FB pin to the point between Q1 and R1 and remove C3. Besides, please connect both EN pin and Gate signal of Q1 to PWM dimming signal. In this way, when Q1 turns off, it won't regulate the output voltage.

    BR

    Gene

  • 0 in reply to Gene Lu
    Guru 29720 points
    Hi Gene-san,
     
    I understood the solution is the following.
    I really appreciate for your support.
     
    Best regards,
    Yaita