User`s guide

Introduction

1.3 MULTI-PHASE SYNCHRONOUS BUCK CONVERTER

If the load current requirement is more than 35-40 amps, more than one converter is

connected in parallel to deliver the load. To optimize the input and output capacitors, all

the parallel converters operate on the same time base and each converter starts

switching after a fixed time/phase from the previous one. This type of converter is called

a Multi-Phase Synchronous Buck converter, which is shown in Figure 1-15. Figure 1-16

shows gate pulse timing relation of each leg and the input current drawn by the

converter. The fixed time/phase is given by Time period/n (or 360/n), where “n” is the

number of the converters connected in parallel.

The design of input and output capacitors is based on the switching frequency of each

converter multiplied by the number of parallel converters. The ripple current seen by

the output capacitor reduces by “n” times. As shown in Figure 1-16, the input current

drawn by a Multi-Phase Synchronous Buck converter is continuous, with less ripple

current as compared to a single converter. Therefore, a smaller input capacitor meets

the design requirement in the case of a Multi-Phase Synchronous Buck converter.

FIGURE 1-15: MULTI-PHASE SYNCHRONOUS BUCK CONVERTER

FIGURE 1-16: SWITCHING WAVEFORM OF SYNCHRONOUS BUCK

CONVERTER

OUT

1PWM

+IQ

3PWM

5PWM

+IQ