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TPS92512 LED Driver Flickering Problem

Ammar Shamsi
Prodigy 60 points
Other Parts Discussed in Thread: TPS92512, TPS92515

Hi,

 I am using LED Driver TPS92512 for battery operated street light new design. 

 No of series LEDs : 3 , LED Srting Voltage is 10V(approx.). The driver is working O.K when the V-in is greater than 12.2V or above OR Dimming PWM signal is 100% i.e High, but when the I/P V is betwwen 10.8V to 12V  and when dimming PWM is given ,the LED light starts flickering (Slowly).

The  frequency used for Dimming PWM is 250Hz.

Please have a look on the attached schematic and let me know possible reasons for this problem.

 

  • 0
    TI__Mastermind 25500 points

    Hello Ammar,

    Does this occur at lower PWM duty cycles or even at say 90% duty cycle? The TPSs92512 BOOT cap discharges when PDIM is low, so if the headroom between Vin and Vout gets low it can discharge quickly to its UVLO threshold because it will not be fully charged at the beginning of the OFF cycle. For that reason we generally recommend at least 5V or so differential for PWM dimming. For designs that need to have less headroom a better option would be the TPS92515.

    Another option is to keep BOOT charged with a resistor from Vin, just limit the BOOT current to <1mA, size the resistor correctly for that. This can keep BOOT from hitting BOOT UVLO which is the cause of the flicker.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Prodigy 60 points

     Thankyou very much Clint for your support.

     Could you please make me more aware on the :

    "Another option is to keep BOOT charged with a resistor from Vin, just limit the BOOT current to <1mA, size the resistor correctly for that. This can keep BOOT from hitting BOOT UVLO which is the cause of the flicker."

  • 0 in reply to Ammar Shamsi
    TI__Mastermind 25500 points

    Hello Ammar,

    You would still need Vin to be BOOT UVLO voltage above Vout but a resistor from Vin (limited to (Vin-Vout)/R < 1mA) could keep it charged. But as I mentioned, this device isn't ideal for low headroom applications. The TPS92515 is much better suited for such applications. 

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Prodigy 60 points
    Thankyou very much for your great support.
  • 0 in reply to Clinton Jensen
    Prodigy 60 points

    Hi Clint,

     As suggested by you, I  have made a new board with TPS92515 , It is working very well. This solved the problem.

     I would like to thankyou again for your really great support.