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LMR36006-Q1: How do we know input current in light load condition with PFM mode?

Yoshiki Ochi
Expert 7555 points
Part Number: LMR36006-Q1

Hi team, 

Could you tell me how to know input current in light load condition with PFM mode?

  • I found that "7.5 Electrical Characteristics" says IQ-nonSW (Operating quiescent current (nonswitching)) is 36uAmax.
    In addition, footnote(2) says "This is the current used by the device open loop. It does not represent the total input current of the system when in regulation". 
    • Does nonswitching means only the duration which is shown in lower figure? So it is not total consumption current in PFM mode, is it correct?
    • Which other current are needed for finding total input current?
  • Does figure. 22 Efficiency could indicate total input current?
    For example, 10mA output current, 5V output voltage, and 12V input voltage, then efficiency is about 82%.
    This shows total input current is 25.4mA, is it correct?
    If correct, could you tell me why this value is much different form IQ-nonSW?

Regards,
Ochi

  • 0
    TI__Expert 7555 points

    Sorry for typo.

    Hi team, 

    Could you tell me how to know input current in light load condition with PFM mode?

    • I found that "7.5 Electrical Characteristics" says IQ-nonSW (Operating quiescent current (nonswitching)) is 36uAmax.
      In addition, footnote(2) says "This is the current used by the device open loop. It does not represent the total input current of the system when in regulation". 
      • Does nonswitching means only the duration which is shown in lower figure? So it is not total consumption current in PFM mode, is it correct?
      • Which other current are needed for finding total input current?
    • Does figure. 22 Efficiency could indicate total input current?
      For example, 10mA output current, 5V output voltage, and 12V input voltage, then efficiency is about 82%.
      This shows total input current is 5.08mA, is it correct?
      If correct, could you tell me why this value is much different form IQ-nonSW?

    Regards,
    Ochi

  • 0 in reply to Yoshiki Ochi
    TI__Mastermind 27045 points

    Hi Ochi,

    • Does nonswitching means only the duration which is shown in lower figure? So it is not total consumption current in PFM mode, is it correct?

              Non switching means the FB pin is biased higher than 1.0V, it's close to the no load condition, so it is not the duration you pointed out, 

    • Which other current are needed for finding total input current?

               Total input current can be tested on actual circuit or refer to efficiency figures

    • Does figure. 22 Efficiency could indicate total input current?----YES
    • This shows total input current is 5.08mA, is it correct?--------------Right

    • If correct, could you tell me why this value is much different form IQ-nonSW?

    At light load condition, device will wake up frequently and switch for dew cycles to charge up output,this will consume much more current than non-switching mode.