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TPS61088: Help to choose the right inductor to achieve EMC compliance

Part Number: TPS61088
Other Parts Discussed in Thread: PMP9778,

Hello,


I'm following the reference design PMP9778, but I need to mount my board using JLCPCB SMT assembly service, and there I couldn't find the CDMC8D28NP-1R2MC inductor. I have hard restrictions about EMI in my project and I would like to choose the best inductor to achieve EMC compliance in my country.

This is the inductor used in the reference design:

CDMC8D28NP-1R2MC

Metal compound molding type construction.
Magnetically shielded
Inductance (uH): 1.2±20%
D.C.R. (mΩ): 7
Saturation current (A): 15.3
Temperature rise current (A): 12.9

The only option available for SMT assembly in JLCPCB wich is compatible with this project about current ratings and inductance is the following:

MWSA1205S-110MT

Molded SMD Power Inductor
Metal material for large current and low loss
Closed magnetic circuit design reduces leakage flux
Inductance (uH): 10
D.C.R. (mΩ): 22
Saturation current (A): 11.8
Temperature rise current (A): 9.3

The manufacturer of MWSA1205S-110MT doesn't says about shileding, only about closed magnetic circuit design to reduce leakage flux, so I would like to know: magnetic shielding is the same thing as closed magnetic circuit for molded inductors? In this case, both MWSA1205S-110MT and CDMC8D28NP-1R2MC will have similar radiated EMI performance?

Thanks,

Geraldo Gomes.

  • Dear Sir,

    Firstly 10uH inductor is really too big for the TPS61088. Suggest you use a 1.2-2.2uH inductor in your design.

    Different inductor has different shielding effect.  So not sure which one is better since I didn't use the MWSA1205S-110MT before.

    Besides the sumida, coilcraft and Cyntec inductor also has very good performance.

  • Hello Helen,

    Thanks for your reply.

    I was planning to use a 10uH inductor because the datasheet says in page 15: "The TPS61088 is designed to work with inductor values between 0.47 and 10 µH" So regarding this subject could you reply te following questions?

    1) Why I must mantain a low inductance value?

    2) A high value of inductance means a low value of ripple current it is not good for EMI performance?

    Regarding the choice of inductor I know that different construction and materials can result in better EMI performance. Is there a real gain regarding EMI performance if I choose the inductor 7447471013 instead the MWSA1004-2R2MT?

    7447471013
    Shielded Radial Leaded Wire Wound Inductor
    https://www.we-online.de/katalog/datasheet/7447471013.pdf
    Inductance (uH): 1.3
    D.C.R. (mΩ): 7
    Saturation current (A): 14
    Temperature rise current (A): 8.5

    MWSA1004-2R2MT
    Molded SMD Power Inductor
    Metal material for large current and low loss
    Closed magnetic circuit design reduces leakage flux
    https://datasheet.lcsc.com/szlcsc/1810181823_Sunlord-MWSA1004S-2R2MT_C149550.pdf
    Inductance (uH): 2.2
    D.C.R. (mΩ): 6.3
    Saturation current (A): 13
    Temperature rise current (A): 13


    Greetings,

    Geraldo Gomes.

  • Dear Sir,

    It's a balance. Please check my reply below:

    I was planning to use a 10uH inductor because the datasheet says in page 15: "The TPS61088 is designed to work with inductor values between 0.47 and 10 µH" So regarding this subject could you reply the following questions?

    1) Why I must mantain a low inductance value? -->with a low inductance , you can use  higher operation frequency. Hence smaller capacitance.  If use a high 10uH inductance, you have to choose a low operation frequency, hence bigger input and output capacitance needed. If the capacitance is not enough, the EMI will also poor. 

    2) A high value of inductance means a low value of ripple current it is not good for EMI performance?-->Many items lead to EMI, inductor is not a key factor.  In some cases, PCB layout is key success of EMI.