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TPS92691: Asking for the TPS92691 design suggestion

SHH
Mastermind 32146 points
Part Number: TPS92691

Hi Sir,

 

My customer would like design LED driver with DC dimming function.

Would you please review two design case with LED spec and provide your comment?

 if TPS92691 is not good option, please let me know what we can recommend. thanks for help!

  1. 10 string, 16pcs LED/string in parallel

        

        2. 10 string, 18pcs LED/string in parallel

       

BR,

SHH

  • 0
    TI__Mastermind 18890 points

    Hello,

    What is the about LED voltage and their tolerances for both case?

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    TI__Mastermind 32146 points

    Hi Tuan,

    Thanks for feedback.

    currently, customer do not has the LED spec.

    customer would like to confirm whether TPS92691 support DC dimming function in generally or not?

    BR,

    SHH

  • 0 in reply to SHH
    TI__Mastermind 18890 points

    Hello BR,

    In general, the TPS92691 will support both DC dimming and PWM dimming.  What is the PWM frequency? 

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    TI__Mastermind 32146 points

    Hi Tuan,

    thanks for feedback.

    the PWM frequency is 20KHz. Customer feedback that TI's LED controller can't support higher frequency, is that right?

    BR,

    SHH

  • 0 in reply to SHH
    TI__Mastermind 18890 points

    Hello BR,

    This is a sort of sampling system and it all depends on the switching frequency, power stage design and how narrow of a pulse that the PWM dimming is. 

    My main worry is the PWM dimming frequency of 20KHz with low duty.  During PWM dimming we tri-state the COMP pin and disable the switching while disconnecting the load with DDRV.  By doing this we let the current in the inductor discharge and when PWM goes hi we enable everything again.  There will be some time before the current in the inductor can charge up the correct level along with current to the load to do the same depending on the power stage design.  This is sort of a sampling system during this time and load current has to reach steady state value before we PWM off again otherwise the control current will not be stable.  This is why I worry about PWM dimming at 20KHz.

    I've recommended to customers to get out evaluation board and test this out with modification as needed for their application.

    Thanks Tuan