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LM25085: Design the Buck converter to zero/low loss at 12V In -> 12Vout

Part Number: LM25085


For a project of mine the user is allowed to use either a 12V or 24V power adapter. Than I need to regulate the voltage if it's at 24V down to 12V. First I thought about using a normal Buck with NFET but It would be complicated to design it to stop/bypassing it if my input voltage is 12V.

Now I tried to use the LM25085. With the basic settings from 14-24Vin-> 12Vout with ~6A I get about about 0.1V+- (as seen in the picture) which is okay but I would like to make it smoother if possible.

But as you can see if I choose 12Vin I get about -0.3V which is way to low. Is there a way to improve this ?

Thanks !


  • Hi Daniel,

    As the duty cycle is 100%, the voltage drop when operating in dropout (i.e. when Vin very close to or below the output voltage setpoint) is based on the output current times the Rdson (of the FET) plus the Rdcr (of the inductor) plus the shunt resistance.

    Vdrop = Vin - Vout = Iout * (Rdson + Rdcr + Rsns)