Iout is the total output current equal to the sum of the individual output currents delivered from the two

sections.

If the PWM signals are synchronized without any delay, the RMS current through the input filter as a

function of duty cycle is :

Irmssync

(δ) =

synchronized (2)

Figure 7 shows Equations (1) and (2) versus the duty cycle.

The maximum RMS current with synchronized PWMs is 1/2 of the total output current and it is obtained

for

δ = 0.5.

In contrast, considering the multiphase PWM, the RMS value is 0 with

δ = 0.5 and the max value of the

RMS value is 1/4 of the total output current. So the maximum RMS current with multiphased PWMs

is a half of that syncronized PWMs.

For every duty cycle condition the RMS current with multiphase application is lower than the case with

synchronized PWMs and it is quite regular for different duty cycles.

It allows to optimize the input capacitor for the real working condition. In the synchronized case the input

capacitor has to be dimensioned for the worst case of

δ = 0.5 that can be far from the real working con-

ditions.

0

t

0

0

1

PWM1

PWM2

t

0

1

PWM1

PWM2

0

0

1

PWM1

PWM2

t

δ<0.5

δ=0.5

δ>0.5

Figure 6. Input current of the two sections for different duty cycle.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0

Irms (

)

δ

Irmssync

(

)

δ

δ

Iout

Iout/2

Iout/4

3Iout/4

Irms

Irmssync

[ A ]

Figure 7. RMS current through the input capacitor with synchronization and with multiphase.

AN1126 APPLICATION NOTE

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