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TPS54JA20: What values for inductor

user6466152
Prodigy 181 points
Part Number: TPS54JA20

Dear all,

I created this design https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=D450732A7EEA1A86 which receives power from USB C PD at 15V

In the past, I had a different design that received power at 12V from an AC/DC transformer. 

I would like to know what is the relationship between voltage, operating frequency and coil inductance. This is because I would like to use the old coils (the one used for the 12V design) instead of buying expensive new ones for the current design.

In the past, I used this coil: www.mouser.at/.../994-XAL5030-801MEB

Now I'm required to use this: https://www.coilcraft.com/en-us/products/power/shielded-inductors/molded-inductor/xal/xal7030/xal7030-102/

Can I use them interchangeably? Why? Why not?

Many thanks!

  • +1
    TI__Mastermind 23640 points

    The  excel calc tool is the easiest way to see the effect of the inductance change or the input voltage change to a design.   Link to Calc Tool   

    If the input voltage goes from 12V to 15V and the inductor, output voltage stay the same, the inductor ripple current will increase and the output voltage ripple will increase. 

    https://www.ti.com/lit/ds/symlink/tps54ja20.pdf#page=27  equation 10 to 13 shows the relationship of the system parameters and inductance.   

    In an overly constrained system with rigid requirements, it may be necessary to change the inductance.  But if there is some flexibility on some specs using the same inductor is possible.