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LM22680: LM22680 and LM25005 - About an upper limit level of the inductor value

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Guru 21045 points
Other Parts Discussed in Thread: LM22680, LM25005, LM5005

Hi Team,

 

Our customer would like to use CCM mode at output current = around 0A to 1.5A.

We understand that we can use CCM mode at light load conditions if we increase inductor value.

So, we guess that the inductor value which is higher than several hundred is necessary.

(I understand that disadvantage is that "Load response" worsens.)

Therefore, we would like to know an upper limit level of the inductor value of each devices.

 

[Conditions]

VIN=8V to 42V

VOUT=5V (+/- 5%)

IOUT=0A to 1.5A

Fsw=420kHz

Synchronizes to External Clock function

 

[LM22680]

I confirmed simulation of LM22680(L=470uH and Cout=6.8uF) by WEBENCH.

Then, phase margin is 57.3deg(please refer to the attached file) so I understand that this device does stable operation.

Could you please let us know if you have any concern and a recommended upper limit level of the inductor value?

 

[LM25005]

I can’t find WEBENCH of LM25005.

Could you please let us know if you have any Calculation tool and a recommended upper limit level of the inductor value?

 

Regards,

Kanemaru

LM22680 L=470uH and Cout=6.8uF sim.pdf

  • 0
    TI__Guru 61595 points

    Since the LM22680 is voltage mode, the most important thing to check is the stability, as you did.

    If Webench says it is OK, it should be OK.

    As always the customer must check the design carefully under all conditions before they commit to production.

    I am not familiar with the LM25005

  • 0 in reply to Frank De Stasi
    Guru 21045 points

    Hi Team,

     

    Thank you for the information.

    And, I have a favor to ask you.

    Could you have the person in charge of LM25005 confirm it?

     

    Regards,

    Kanemaru

  • 0 in reply to Hide
    TI__Guru 56402 points

    Hi Kanemaru,

    You can use the LM5005 WEBENCH model for further guidance. There is an internal 25uA current source contributing to slope compensation (see equation 2 in the LM25005 datasheet), and using a very large inductance could shift the emulated current-mode control archtiecture towards an undesirable double-pole voltage-mode like behavior. We generally recommend a minimum load current if CCM operation is required.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Guru 21045 points

    Hi Timothy-san,

    Thank you for the information.

    I understand. Thank you very much.

    Regards,

    Kanemaru