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LM2595-ADJ inductor selection

Rene Mann
Prodigy 20 points
Other Parts Discussed in Thread: LM2595, LM22675

Hello all,

I have to design a step down converter using LM2595 adjustable version. The input voltage range should be 12-24V. The output voltage should be set by different assembled programming resistors to 3.3V or 5V.

For the different voltages i get different inductor values (47uH @ 12Vin/3.3Vout, 100uH @ 24Vin/5Vout) by formula from datasheet.

What happens, if i assemble a 100uH inductor and operate the circuit within the "wrong" voltage range (e.g. 12Vin/3.3Vout)? Is the circuit working anyway? Do i lose efficiency only?

Thank you in advance!

Rene Mann

  • 0
    TI__Genius 10095 points

    Hello Renee,

    In general, you want to design the inductor for the highest input voltage and an output voltage in the middle of your range.  In your case, I would enter 12-24Vin into webench (located on the right hand side of the product folder) and 4Vout.  This should get you a design that is stable and has appropriate ripple current in the range of your design. 

    There are many different control topologies where inductor selection effects stability differently. Also for inductors, the power losses are proportional to DCR (DC Resistance) and the amount of current ripple in your design (Core losses).  So sometimes a larger inductance value, although it has larger DCR losses might have less Core Losses.

    Webench will calculate the efficiency for your different input voltages and you can see the effect of different output voltages by repeating the simulation.

    If your goal is to reduce overall solution size, you might want to look at out newer LM22675.  It is in a similar package to the LM2595 but operates at a higher switching frequency.  This leads to a smaller inductor.

    Regards,

    Marc