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TPS61165: URGENT PWM Dimming is not working very well

DURAISAMY prabhakaran
Prodigy 85 points
Part Number: TPS61165

Hello Everyone,

I have recently devloped an product by using TPS61165 which consists of 8LEDS by limiting 20mA current maximum when i provide direct PWM signal (Function genrator) at 10KHz  at 50%duty cycle with 3V3

then led started flickering later i have started changing either the frequency or an input voltage from  Vin 3V3 to 3V1  it is started functioning correctly 

again if i increase the voltage from VIN 3V3 to 5V the led no even working  i dont understand exactly how it is functioning even though i have read the datasheet  so many times repeatedly

Could you please suggest me is there is any limitation for this device or any other particular conditions has to be taken into account in order to understand the functionality

is there is any dilemma between CRTL pin voltage and frequency variation with respective duty cycle

Finally i have made conclusion when i provide CTRL PIN VOLTAGE (PWM) between 1.2V TO 3.2V then only led are working other than it is turned off completely for higher voltages why i am having this problem 

any help or ideas would be greatly appreciated

  • 0
    TI__Mastermind 22745 points

    Hi sir,

        From your description, it is a little strange and PWM dimming frequency should not have much effects on the dimming. But I want to makes ure with you about the output volatge and could you share me your schematic, I'd like to check the schematic for you.

    Regards

    Sean

  • 0 in reply to Sean Zhou
    Prodigy 85 points

    Hello sean 

    Thank you for your kind effort to help me i have done simply the suggested application diagram in my schematic 

    i have provide an DC it is functioning correctly but when i provide an PWM signal from Function generator it is getting turned of when i reach above 3.2V i did not understand it should be functioning 3V to VIN but it is not functioning after 3.2V for 10khz 

  • 0 in reply to Sean Zhou
    Prodigy 85 points

    Hello Sean

    Thank you for your kind suggestion 

    actually my exact problem is not the PWM frequency but PWM amplitude

    I have generated PWM SIGNAL from NXP microcontroller with 3V3PP 30KHz and then i connected that PWM signal in TPS61165 LED DRIVER CTRL pin which is working fine

    Similarly I have generated PWM signal from ARDUINO with 5VPP 30KHZ then i do the same principal to CTRL pin then LED is not even turned ON

    this is my exact problem why it is not working for 5V PWM signal 

    i would like is there is any PWM voltage limitation beyond 3V3 it will not function?

    then why the TPS61165 datsheet tells CTRL pin voltage limitation 1.2V to 18V for PWM 

    Any help or suggestions would help me greatly to advance in my project i am really blocked at this point

    Thank you

  • 0 in reply to DURAISAMY prabhakaran
    TI__Mastermind 22745 points

    Hi Sir,

        Have you observed the PWM signal to our TPS61165 from the "CTRL" pin, I guess that maybe your Arduino has low capability for the IO pull up , it maybe pulled down when connect to TPS61165. It is clear that is caused by your PWM signal, not our devices. Or you can use signal generator to test the PWM amplituide.

    Regards

    Sean

  • 0 in reply to Sean Zhou
    Prodigy 85 points

    Hello Sean,

    Thank you for your replay

    Actually i have tested by generating PWM signal from Function generator with 5V amplitude at 30KHz  for that also L ED is not turning ON

    i dont understand why it is mentioned in datasheet CTRL pin has to function for voltage range between 1.2V to 18V but for my application it is functioning only for 1.2V to 3.3V only 

  • 0 in reply to DURAISAMY prabhakaran
    TI__Mastermind 22745 points

    Hi Sir,

        For this strange phenomenon, I don't have more commons on this, have ever changed any chips or board to test again? We have never met such kind of phenomenon.

    Regards

    Sean

  • 0 in reply to Sean Zhou
    Prodigy 85 points

    thank you for your response*

    is there is any evaluation board which i can make the same test in order to review the exact problem could you suggest me some tariff reduced boards which could be affordable for me

    Thank you

  • 0 in reply to Sean Zhou
    Prodigy 85 points

    Hello Sean

    Could you please tell me what is the maximum amplitude on the CTRL PIN for only   PWM signal have  you tested on the evaluation boards

    Beacause i have generated 3.3V PWM signal 10KHz with 50% duty cycle then the 8 LEDS are turned ON

    but when i increase only the HIGH Level ampitude of the PWM signal ( not Vin )around 4.1V then the 8 LEDS are turned OFF

    that is not good behaviour of this component

    Could you please tell me what is maximum apmlitude of PWM SIGNAL on CTRL pin when it is not pulled high by default because i am trying to do the dimming by using PWM signal from microcontroller

  • 0 in reply to DURAISAMY prabhakaran
    TI__Mastermind 22745 points

    Hi Sir,

         When we do the test in our lab, what we need to do is to make sure the amplitude of "CTRL" is below the supply voltage, usually we apply a 3V/3.3V to the "CTRL" pin or just pull up the "CTRL" pin to the Vin through a resistor.

    Regards

    Sean