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TPS61500 minimum duty cycle for startup

Bob Plott
Prodigy 230 points
Other Parts Discussed in Thread: LM3423

When using analog dimming, Cdim = 1uF, it seems that 40% is the minimum duty cycle required to begin operation. This is the case for PWM frequencies from 200Hz to 10kHz. Unfortunately, my sig gen doesn't allow me to change DC of the fly, so I can't verify whether the DC can be reduced after startup. Am I missing something here? Or is this similar to the operation described in the post titled "LM3423 start-up significant delay with low PWM dimming level"?

Regards, Bob

  • 0
    TI__Mastermind 40080 points

    Hi Bob,

    You mentioned that " it seems that 40% is the minimum duty cycle required to begin operation" , where did  you get this iformation? Our designer told me that they didn't set this limit internally.

    BR,

    Helen

  • 0 in reply to Helen chen
    Prodigy 230 points

    Helen,

    This 40% was the empirical result of testing with a pulse gen on the PWM input pin. As stated, in OP this held true for pulse rep rates of 200Hz to 10kHz.

    I've yet to get back to this to test whether reducing the DC from 40% after startup has the expected effect.

    Best regards,

    -Bob