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Original question:

LM5023: Valley switching operation

LM5023: Valley Switching: "Lp used" Meaning

jacob scaria
Prodigy 110 points
Part Number: LM5023

Hi,

In lm5303 Datasheet, Section 8.2.2.3, for finding Cd equation, What is the meaning of term " Lp_used ". Is the value that should be used here is Lp?

For the exampe give in datasheet Lp=400uH

Jacob

  • +1
    TI__Mastermind 33970 points

    Hello Jacob, 

    I believe that the term "Lp_used" is derived from the distinction made between "Cd" and Cd_used" in the text following equation (54).  
    The author probably did not realize (at the time) that this inconsistency is the only instance of "Lp_used" throughout the datasheet. 

    Note that equation (53) relates t_dlyqr to RFF x Cd, so of course, Cd = t_dlyqr/RFF.
    Also, equation (52) equates t_dlyqr to an expression containing "Lp", and this expression is substituted in for t_dlyqr in equation (54).

    So, Lp_used is the exactly same as Lp, and I think "Lp_used" was inadvertently coined while the datasheet author was drawing a distinction between the overall Cd needed for timing and the external value required (Cd_used) when accounting for the already-present 20-pF pin capacitance. 
    Please simply consider "Lp_used" to be identical to "Lp".

    Regards,
    Ulrich