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TPS92513 driven LED glows when PWM duty cycle is 0

Bolin Qu
Prodigy 50 points
Other Parts Discussed in Thread: TPS92513, LM3414, LM3409, LM3404, LM3406, LM3407, LM3402

We are using TPS92513 to drive 2 chains of 3 serial LEDs. We are able to dim the LEDs with PWM signal through PDIM pin. The frequency of PWM is 250Hz, with 256 steps from 0% to 100%. We are using IADJ to set driving current, the UVLO pin is open. The LEDs keep glowing when we decrease PWM duty cycle slowly to zero at 11-13V input voltage. We can totally turn off the LEDs when decrease duty cycle quickly at 11-13V input voltage or slowly at 15V input voltage. The LED glows when we power on the light at 11-13V input voltage with 0 duty cycle PWM. The LED turns off when we power on the light at 15V input voltage with 0 duty cycle PWM. We want the LED totally off when PWM duty cycle is 0.

There is a ~300mA spark at the rising edge of our PWM digital dimmed 230mA current. Is there any way to lower the current spark? 

Thanks,

Bolin

  • 0
    TI__Mastermind 25500 points
    The TPS92513 has a minimum PWM dimming duty cycle, generally about 1% (100:1) due to the way it charges the bootstrap capacitor. It needs that 1% on time to charge the cap connected to BOOT. So you are limited to 1% and then would need to pull UVLO to ground to make the current zero. The LEDs glow because after you enter BOOT uvlo the part will try to start again periodically to charge BOOT because it is still enabled. Entering boot UVLO while PWM dimming at low duty cycles is also the likely cause of the current overshoot as well, I have seen it in the lab. This is another reason the minimum is limited with this device. In any case, if this is still an issue there are other buck converters that will do this function and you can go to 0% duty cycle. I don't know your exact current/voltage requirements but you can check out the LM3402, LM3404, LM3406, LM3407, LM3409, or LM3414. They are all capable of 0% PWM duty cycle and will turn the LEDs off.
  • 0 in reply to Clinton Jensen
    Prodigy 50 points

    Thank you for the quick reply.

    The Vin range for our light is 11~26V. I have tested LM3402 EV board. The average current and ripple vary with different Vin.