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LM3489: inductor selection

daniel
Genius 5095 points
Part Number: LM3489

Hi Team,

We use LM3489 on Type C PD application. (5V_3A /  9V_2A / 12V_1.5A / 15V_1.2A / 20V_1A)

I use 8.2.2.1 Inductor Selection equation, but can't get reasonable value. Please help to confirm if we can use 4.7uH. Thanks.

Vin=22V, VDS=as attached PFET datasheet(DMP3056LSS), VOUT= 5V_3A /  9V_2A / 12V_1.5A / 15V_1.2A / 20V_1A,  D(Duty cycle) & f(Operating frequency)=as attached waveform.

4.7uH : duty 76.68% frequency 259KHz

6.8uH : duty 76.01% frequency 227.9KHz

DMP3056LSS.pdf

Thanks

  • 0
    TI__Expert 5910 points

    Daniel,

    I would recommend using 10uH for the Vo=5V and 22uH for higher Vo such as 9V,12V,15V etc.

    Using 4.7uH pushes the frequency too high.

    Step 1: Set  delta I to Iout ratio =0.3 to 0.4  and then calculate delta I

    Step 2:  Substitute L with 10uH and see what freq you get. In the equation D changes as per your output voltages.

    Regards,

    Mathew

  • 0 in reply to Mathew Jacob1
    Genius 5095 points

    Dear Mathew,

    Thanks for your reply.

    We want to reduce the inductor because the temperature on 6.8uH is too high, and 4.7uH would reduce the inductor temperature.

    (5V_3A loading)  6.8uH: 92℃,  4.7uH: 75℃

    Could you give us some advice to reduce the operating temperature? schematic as attached.

    Thanks