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LMR23630: About LMR23630 at light load

GARAM AN
Intellectual 1990 points
Part Number: LMR23630

Hello,

The LMR23630 changes control mode automatically from PWM to PFM at light load.

What is the condition of light load for this buck? when the buck changes mode from PWM to PFM?

Thank you

  • 0
    TI__Mastermind 22301 points

    Garam,

    The LMR23630 will go from PWM into discontinuous conduction DCM when the output current is 1/2 the inductor ripple current as described in the datasheet 8.4.2.

    That ripple current depends on the Fsw, VIN, VOUT and buck inductance.

    As the output current is decreased further in DCM, the no-conduction "off-time" will increase while the conduction off-time and conduction on-time will decrease to keep the same switching period. The decrease in conduction time will lead to decrease in ripple current as well.

    As described in the datasheet (8.4.4), "When either the minimum HS switch ON-time or the minimum peak inductor current (300 mA typ) is reached the switching frequency decreases to maintain regulation" and the device will enter PFM mode. This ties into the PFM detector discussed in another thread.

    Hope that helps,

    -Orlando