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Inductor Related to 15V-47V to 48V Boost using TPS40210

shakti ahuja
Prodigy 40 points
Other Parts Discussed in Thread: TPS40210

When designing the circuit using TPS40210 module and giving the specifications as voltage range 15 to 47V @ 1.25A and temperature to be 70 deg C in the Webench tool it is saying to use customised Inductor. Can you please specify why any vendor for the Inductor.

Why the current requirement of the Inductor is specified to be 6A, even more than 3 times the rated current? Also what can be the Maximum DC resistance of the Inductor?

  • 0
    TI__Mastermind 35165 points

    Hi Shakti,

    It specifies a custom inductor because there are not any in the database for this design.

    Part of the reason for this is you're max input voltage is very close to your output voltage. WEBENCH's design equations choose the inductor to limit the current ripple using the maximum input voltage. A relatively large inductance is needed to meet the default target with 47V input to 48V output. (See Equation 35 in the datasheet). In reality a smaller inductance can be used for this design.

    The current requirement for the inductor is 6A because in a Boost topology, the inductor sees the input current. Not including efficiency of the design, the input current is approximately (VOUT*IOUT)/VIN = 4A using the minimum input voltage. WEBENCH shows this as Iin Avg in the Operating Values table. You must also account for ripple current in the inductor and this is SW Ipk in the Operating Values table. Lastly it is recommended to leave some margin with the saturation rating of the inductor so it does not become saturated during transient conditions.

    The DCR should be kept as low as possible to reduce losses in the design and is typically on the scale of tens of mOhms.

    By reducing the maximum input voltage of your design to 45V instead, WEBENCH is able to find an inductor that fits. The PM2120-470K-RC from Bourns. This is 47uH, 19mOhm, and 8.20A. Other inductor vendors will likely have some options if a 47uH inductor is used instead. Decreasing your inductance even further will increase your options for inductors with a high enough saturation current rating. I do not see any reason the design with a 45V max input will not work up to a 47V input too.

    Hope this helps you out, let me know if you have any additional questions.

    Regards,
    Anthony