• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 461 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM3410-Q1: pwm dimming

Jin-Suk Choi
Intellectual 1630 points
Part Number: LM3410-Q1
Other Parts Discussed in Thread: LM3410

Hi~

Customer is under design with LM3410-Q1, but PWM dimming can't implement like datasheet.

Channel current is 540mA, LED Vf is 9.1V(3S).

Due to high channel current, PWM off duty can't meet low for whole frequency range(300~20kHz), so PWM dimming linearity is poor.

As customer and I feedback, LM3410 can't use such a high channel current(more than 500mA) for PWM dimming. How about your idea?

When decrease output cap smaller, boost stability collapse so can't regulate output, when increase output capacitance, can't meet off low off duty.

:-(

If you have any idea, please, advise.

Thanks.

  • 0
    TI__Mastermind 25500 points

    Hello,

    Boost converters, especially current mode control, are generally slower since they require a certain amount of output capacitance for stability. Because of that linearity will suffer at higher frequencies. It will be worse at higher currents because you generally need more output capacitance and the dynamic resistance of the LEDs at high current is usually much lower (the output cap will discharge more during the OFF time).

    Unfortunately there isn't much that can be done about that. The datasheet shows up to 20kHz but boost regulators are really best at 1kHz or lower if you need linearity. You could maybe try an NFET on the low side of Cout to disconnect the capacitor during the off time so that it doesn't discharge very far. That method is used with some other boost regulators.

    Regards,

    Clint