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Original question:

LMR38010: Spread Spectrum at light load

LMR38010: LMR38010 PFM SS & AUTOMODE

kwon
Intellectual 850 points
Part Number: LMR38010

HI~

1. datasheet 3page [5 Device Comparison Table] LMR38010SDDAR (FPWM=NO, SS=YES)

- If FPWM=NO, it operates as PFM. Can SS also be used?

- In the link below, it is said that SS does not operate in PFM mode.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1234008/lmr38010-spread-spectrum-at-light-load/4661833?tisearch=e2e-sitesearch&keymatch=lmr38010%20fpwm#4661833

2. Does the datasheet 16page auto mode only apply to FPWM=YES (LMR38010FDDAR, LMR38010FSDDAR)?

Best Regards,
 
KWON.
  • +1
    TI__Genius 13735 points

    hi, Kwon,

    AT PFM mode when light load the frequency will drop. Once the frequency is not controlled by internal clock the SS function will not work. FPWM mode even light load the frequency is fixed so SS function works.

    Elena

  • +1 in reply to Elena Gao
    Intellectual 850 points

    Hi~

    Does the LMR38010SDDAR (FPWM=NO, SS=YES) have SS function, but it does not work on light load, and does SS work when it is over 100mA?

    Is it wrong to say that SS is not working in PFM mode in the link answer above?

    Among the questions above, is AUTO MODE applicable only to FPWM=YES?

    There is no mention in the datasheet.

    Thanks.

  • +1 in reply to kwon
    TI__Genius 13735 points

    hi, Kwon,

      :"FPWM=NO, SS=YES) have SS function, but it does not work on light load, and does SS work when it is over 100mA?  "

    ----yes , you understand is right,

     usually we talked PFM is mainly focused on light load, because heavy load PFM mode and FPWM mode device is the same in CCM.

    Auto mode is PFM, which means it can auto change DCM and CCM. 

    please refer to DS search mode to understand it .

    Elena

  • +1 in reply to Elena Gao
    Intellectual 850 points

    Hi.

    The first question was solved. Thank you for your answer.

    AUTO MODE has not been resolved.

    DATASHEET 16PAGE 8.4.1 AUTO MODE explains as follows.

    [In auto mode, the device moves between PWM and PFM as the load changes. At light loads, the regulator operates in PFM. At higher loads, the mode changes to PWM.]

    LMR38010SDDAR cannot operate as AUTO MODE because it has no FPWM function, and LMR38010FDDAR/LMR38010FSDDAR has an FPWM function, it will be PWM<->PF changed to AUTO MODE.

    Then, FPWM=NO is only PFM, so it cannot be operated in auto mode, and isn't only FPWM=YES operating in automatic mode?

    KWON.

  • +1 in reply to kwon
    TI__Genius 13735 points

    No, first you need to clear is, FPWM F is stand for FORCE, means the frequency is FIX without change by loading. 

    as in DS  "In auto mode, the device moves between PWM and PFM as the load changes. "This is right , we can also say, In FPWM the device will not " moves between PWM and PFM" .

    Refer to part number, LMR38010FDDAR, the F is stands for FPWM, without F will be auto mode.

  • 0 in reply to Elena Gao
    Intellectual 850 points

    Thank you for the detailed explanation.