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LM63625-Q1: boundary condition between PFM and PWM

Shinji Tsuji
Genius 12358 points
Part Number: LM63625-Q1

Hi team,

I would like to know the load current at which MODE change from PWM to PFM.

I understand it depends on Vin/Vout/Fsw and inductance of the coil, so here is my conditions below.

Vin = 24V and 28V

Vout = 5V

L = 2.2uH

Mode : AUTO

It is also helpful if you can share the equation to get the boundary condition.

I think the PFM starts when the load current decreased to the level at which the device starts DCM operation.

If there are other condition, please let me know.

regards,

  • 0
    TI__Mastermind 27030 points

    Hi 

    1. fro CCM come to DCM, which means the inductor current go down to 0, the inductor current = Iout(DC)+Iripple(ac)

    so the boundary of CCM and DCM is Io=0.5Iripple . Iripple=(Vin-Vo)*D/L*fsw

    2. after the inductor come to DCM, by Io decrease, the duty will decrease, with means Ipeak of inductor current will smaller by the Io.

    when Ipeak=Ipeak_min, then it come to PFM mode, which means keep inductor peak current constant, and reduce the frequency for holding the output voltage.

    Thanks

    Daniel Li