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LM3404HV: The duty cycle about the LED drivers

Jenny Lu69
Expert 1810 points
Part Number: LM3404HV
Other Parts Discussed in Thread: LM3409, LM3414HV, TPS92510, TPS92513HV

Hi e2e team,

I received a inquiry from a customer who used LM3404HV, and also made me confused about it.

The lm3404HV is used to output DC42 volts in his design, and he found only when input voltage reaches 47-48v, the 42v output can be get. A 5-6v dropout voltage is too high for him, he wanted to know if we have a lower dropout voltage LED driver could meet his design, that is to say a higher duty cycle LED driver will be better.

And I seek for many products in LED driver field, but they rarely mention the duty cycle in the datasheet, instead of that the duty cycle of PWM dimming was interpreted in real detail. Could you give some directions about it, and is there other drivers similar to LM3404HV but has a higher duty cycle?

Thanks a lot.

Best Regards,

Jenny

  • 0
    TI__Mastermind 28655 points
    Hello Jenny,

    Minimum off-time is 270 nS. I don't know what switching freqeuncy or Ron he is using. This requires the off-time to be long enough for the boot capacitor to recharge. The LM3409 does not require this if they need a high side switch. Lowering the switching frequency may help as well.

    Regards,

    Irwin
  • 0 in reply to Irwin Nederbragt
    Expert 1810 points
    Hello Irwin,

    It's right, I've already told him.

    However, I cannot find the minimum off-time for below chips, would you please tell me?

    ------LM3414HV

    -----TPS92513HV

    -----TPS92510

    Thanks for your patient help.

    Regards,

    Jenny
  • 0 in reply to Jenny Lu69
    TI__Mastermind 28655 points
    Hello Jenny,

    For the LM3414HV: Low side MOSFET, no issue

    For the TPS92510, from the datasheet: The TPS92510 is designed to operate up to 100% duty cycle as long as the BOOT to PH voltage is greater than 2.1V. If the BOOT capacitor voltage drops below 2.1 V, then the BOOT UVLO circuit turns off the MOSFET,
    which allows the BOOT capacitor to be refreshed. The current required from the BOOT capacitor to keep the
    MOSFET on is quite low. Therefore, many switching cycles occur before the BOOT capacitor is refreshed. In this
    way, the effective duty cycle of the converter is quite high.

    For the TPS92513HV: Similar to the TPS92510

    Regards,