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LMR38020: LMR38020FDDAR

SWENGWOO LEE
Intellectual 270 points
Part Number: LMR38020

HI

VSUP_POE : 37~57V

VOUT : 34V

1. When input voltage is applied to the LMR38020, it initially outputs 34V then gradually decreases over time (under no-load conditions). Can you tell me why?

2. When a load is applied while the voltage is dropping (approximately 17V), it causes a significant inrush current. Is there a solution to this issue?

  • 0
    TI__Mastermind 30955 points

    Hi Swengwoo,

    Sorry to hear you are having trouble with your design. 

    It could be a few issues.

    1) Can you take a waveform of the input voltage, output voltage, BOOT, SW, and BOOT-SW? I suspect in the design that the output voltage dropping during startup could be the output capacitor is not being recharged. Can you check your boot-to-sw capacitor C140 and make sure that it is not discharged?

    2) What load are you running such that the inrush current occurs? I suspect it is related to the first issue in that if your output voltage is so low, and the error amplifier requires a large amount of energy to charge the capacitor, you will see a big spike in current. 

    3) Can your input power supply support the load application? During start-up, the waveform should be smooth.

    Thanks,

    Richard