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TPS61195: LED blinking at low duty cycle of PWM

Nicky Lim
Genius 3195 points
Part Number: TPS61195

Hello,

Make LED back light board using TPS61195 as attached.

Using Analog mode PWM interface, and PWM frequency is 3.9KHz. 

Using 16steps of PWM duty cycle (from 4% to 90%)

At the low duty cycle (1 to 4 step : Anode Current 50mA Under), LED blinking is occurred.

 Could you check attached schematic and let me get the result ASAP?

Regards,

Nicky

TPS61195 Sch.pdf

  • 0
    Genius 3195 points
    Hello,

    Is there any update?
    Please let me get your reply ASAP.

    Thanks & Best Regards,
    Nicky
  • 0 in reply to Nicky Lim
    TI__Expert 4550 points
    Hi Nicky,
    Have you checked Vin and SW signal of IC? Have you seen anything different with normal operation?

    thanks
    Caryss
  • 0 in reply to Caryss Li
    Genius 3195 points
    Hi Caryss,

    It works fine with normal operation, but only happens with low duty cycle.
    Is there any way to improve this symptom with low duty cycle?
    According to datasheet, under 10% duty cycle, efficiency dropped rapidly. Is it a root cause of this symptom?

    Regards,
    Nicky
  • 0 in reply to Nicky Lim
    TI__Expert 4550 points
    Hi Nicky.
    When you dim down, could you please observe the SW signal to see if the IC enters skip mode?
    For the efficiency, the power loss consists of DC loss and AC loss. Basicly the DC loss is related with you power, lower power, lower loss, such as loss on DCR of inductor and mosfet. The AC loss is not that much , still part of, related with power. When you dim down ,the total power is lower, the AC loss takes more propotion and not decreases as much as total power, so the system effieicncy will be lower than full load.

    BR
    Caryss