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LMR33630: Inductor and output capacitor

Takashi Yamaguchi
Genius 13310 points
Part Number: LMR33630

Hi team,

I'm proposing the LMR33630 to my customer. Could you help with the questions below from the customer?

Here is the requirement

Vin = 23.2V to 25.8V

Vout = 5.0V

Iout = 2.8A

Fsw=400kHz(A version) or 2.1MHz(C version)

1. Regarding the external parts selection.

Could you tell me the recommended inductance and output capacitance value for each Fsw?

For the inductor, could you also provide the required value for the DC superposition rated current Isat?

2. Could you tell me the output voltage accuracy when the converter is operating in PFM mode?

Regards,

Yamaguchi

  • 0
    TI__Mastermind 34745 points

    Hi Takashi,

    10uH for 400KHz

    2.2uH for 2.1MHz

    Inductor saturation current >=5A 

    PFM mode will have about additional +0.08% drift at no load condition. 

    B R

    Andy

     

  • 0 in reply to Andy Chen
    TI__Genius 13310 points

    Hi Andy,

    Thanks for the answer.

    I calculated the current ratio to Iout(max), and confirmed the ratio is between 20% to 40%.

    When the inductance is 10uH for 400kHz and Vin is 24.5V(typ), the ripple current would be around 0.995A. The ratio would be 35.5%(=0.995A/2.8A).

    When the inductance is 2.2uH for 2.1MHz and Vin is 24.5V(typ), the ripple current would be around 0.861A. The ratio would be 30.75%(=0.861A/2.8A).

    Could you tell me the recommended output capacitance as well?

    For the 400kHz, is the recommended capacitance 4 x 22uF from table.2 in the d/s?

    For the 2.1MHz,is the recommended capacitance 2 x 22uF from table.2 in the d/s?

    Regards,

    Yamaguchi

  • 0 in reply to Takashi Yamaguchi
    TI__Mastermind 34745 points

    Hi Yamaguchi,

    for 400kHz, recommended capacitance is 4 x 22uF

    For the 2.1MHz, recommended capacitance is 2 x 22uF.

    All capacitor should be 16V or higher rating.

    B R

    Andy