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LM25141: About DCR current sensing

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Guru 21045 points
Part Number: LM25141

Hi Team,

 

We would like to use the DCR current sensing at the following conditions.

I calculated “current limit at DCR current sensing” and "CCS" and "RCS" according to the datasheet.

 

[Conditions]

VIN=4.5V to 20V

VOUT=3.8V

IOUT=3.0A(max)

Fsw=440kHz

LOUT=6.8uH (DCR is 18.4mohm)

(Current limit is around 3.88A at DCR current sensing according to calculation (12))

 

[My result]

-Current limit is around 3.88A

-CCS is 3.3uF

-RCS is 100ohm

 

*“LOUT/RDCR” is 0.000369 and “CCS*RCS” is 0.00033.

So “CCS*RCS” is nearly equal to “LOUT/RDCR”.

 

Is my understanding correct?

Could you please let us know if you have any concern and recommended other value?


 

 

Regards,

Kanemaru

  • 0
    TI__Genius 11040 points

    Hi Kanemaru-san,

    Yes, your understanding is correct.  The objective is to choose Rcs and Ccs, so RcsCcs=Lout/Rdcr.

    As designed I also calculate:

    Rcs*Ccs=.00033

    Lout/Rdcr=.0003696

    The percent difference between these two values is approximately 11%.  I would recommend changing Rcs to 110 Ohm; then, Rcs*Ccs=.000363.

    As the datasheet mentions, the PCB layout will be critical to ensure noise and DC errors do not corrupt the current-sense signals.  When you begin layout, make sure to follow the PCB layout guidelines.

    Best Regards,

    Katelyn Wiggenhorn

  • 0 in reply to Katelyn Wiggenhorn
    Guru 21045 points

    Hi Katelyn-san,

    Thank you for the information.

    I understand. Thank you very much.

    Regards,

    Kanemaru