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LMR62421: LMR62421 response too low and voltage drop too much when the load transisent

Betty Guo
Expert 7300 points
Part Number: LMR62421

Hi,

customer use LMR62421, the shematic as below, and found that the voltage will dorp from 12V to 9.5V when the current change from about 0mA to 800mA(peak).

input: 5V; output 12V, current 800mA(peak)

the waveform as below: yellow is 12V output; green is current. 

you can see that when the current start up, the output voltage will drop, the maximum drop to 9.5V.

could you give some suggestions to improve the dynamic response ？thank you

  • 0
    TI__Mastermind 34201 points

    Hi Betty,

    What if they add load current slowly, could the output voltage keep stable at 12V at 800mA?  One 10uF/16V ceramic capacitor is not enough. Please use 2 in parallel.

    0.8A output current is too high for LMR62421. LMR62421 switch current limit is 2.1A(minimum), 3A(typical). Assuming the efficiency is 85%. The averaged input current is 12*0.8/5/0.85=2.25A. The inductor peak current may trigger current limit threshold.