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LM53625-Q1: Why does LM536255LQ have better EMC at 24V to 5V conversion ? (comparing to LM536255Q )

PYTsai
Genius 9325 points
Part Number: LM53625-Q1

Hi 

We done the measurement, test result as picture shown below. 

1. Why does LM536255LQ have better EMC at 24V to 5V conversion ? (comparing to LM536255Q )

2. Are there different internal architecture of LM536255Q and LM536255LQ?

  • 0
    TI__Mastermind 27030 points

    HI

    no different at architecture , based on device table, LM53625LQ is fixed 5V with spread spectrum, LM536255Q is only fixed 5V without spread spectrum. I don't know the mean of second picture marked " spread function should be off", it should be a factory option

    Thanks

  • 0 in reply to Daniel Li14
    TI__Genius 9325 points

    Daniel,

    Datasheet section 8.5 Spread-Spectrum Operation mentioned that input voltage above approximately 21 V disables spread spectrum. 

    So we thought at 2nd waveform LM536255LQ spread spectrum should be off, because the input is 24V. 

    At 24V input, both device no spread spectrum but EMI performance are different, customer would like to know why? 

  • 0 in reply to PYTsai
    TI__Mastermind 27030 points

    Hi

    are both test in the same board or different board?

    and can customer check the SW waveform include raising and falling and frequency?

    Thanks