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Original question:

LMR38010: LMR38010 -HS AND LS SWITCH CURRENT LIMIT

LMR38010: LMR38010 using it for 1A output current .

Vasu Poojary
Intellectual 450 points
Part Number: LMR38010

Tool/software:

Hello Expert,

I am using LMR38010 for designing Buck converter from 11.5V to 36V to 10.5V output @ 1A .

Switching frequency : 700KHz, Inductor used 47uH.

Max inductor current is around 1.2A.  (Delta IL of 0.2A )

From Datasheet.

Low side switch min current is 0.9A and Max current is 1.5A

From above inductor current , Low side switch current starts with negative slope and in our case it will be 0.8A to 1.2A.   Since datasheet mentions the Low side switch limit is 0.9A to 1.5A , if in case of lower tolerance (0.9A) how load current of 1A or inductor peak current of 1.2A  maintained through low side switch ? 

Our understanding is during the positive slope of inductor current  High switch of IC will be ON and during negative slope of inductor current low side switch of IC will be ON.  So when inductor current is above 0.9A (worst case tolerance ) then IC will go to protection ?

Is there is any misunderstanding from our side ?

Thanks

regards

Vasu

  • 0
    TI__Genius 9260 points

    Hi Vasu,

    The low side current limit actually monitors the valley current (minimum inductor current). As long as that is below 0.9A it should be good. With 0.8A to 1.2A inductor current ripple, the peak (1.2A) and valley (0.8A) are below the HS and LS current limits (1.3A and 0.9A minimum) respectively. Therefore it should not pose any issue.

    Regards,

    Niranjan

  • +1 in reply to Niranjan Nair
    Intellectual 450 points

    Hello Niranjan,

    Thanks for quick clarifications .   In this case is Max inductor peak current is limited to 1.3A ? (HS current limit , lower tolerance limit )

    Can you please explain , what it means of high side current limit of  1.3A to 1.9A ?

    For Low side current limit only 0.9A (lower limit ) is significant , typical and max is not important ?

    thanks

  • 0 in reply to Vasu Poojary
    TI__Genius 9260 points

    Hi Vasu,

    The range given is the distribution of that parameter among different ICs. For eg. most ICs will have the high side limit close to the typical 1.6A, but it can also be as low as 1.3A and as high as 1.9A in some ICs.

    When designing, it is important to take the minimum of the current limits as those will be the worst case. If the peak/valley during operation is less than the minimum current limits, it should not pose an issue for any IC you use.

    Regards,

    Niranjan