Specifications

dsPIC33F/PIC24H Family Reference Manual

43.16.3 Multi-Phase PWM

The Multi-Phase PWM, illustrated in Figure 43-48, uses phase shift values in the PHASEx

registers to shift the PWM outputs with respect to the primary time base. Because the phase shift

values are added to the primary time base, the phase shifted outputs occur earlier than a PWM

signal that specifies zero phase shifts. In Multi-Phase mode, the specified phase shift is fixed by

the design of the application. Phase shift is available in all PWM modes that use the master time

base.

43.16.3.1 MULTI-PHASE BUCK REGULATOR

Multi-Phase PWM is often used in DC-to-DC converters that handle fast load current transients,

and need to meet smaller space requirements. A multi-phase converter is essentially a parallel

array of buck converters that are operated slightly out of phase with each other. The multiple

phases create an effective switching speed equal to the sum of the individual converters.

If a single phase is operating at a PWM frequency of 333 kHz, the effective switching frequency

for the circuit, illustrated in Figure 43-48, is 1 MHz. This high switching frequency greatly reduces

input and output capacitor size requirements. It also improves load transient response and ripple

figures.

Figure 43-48: Multi-Phase PWM

43.16.3.2 INTERLEAVED POWER FACTOR CORRECTION (IPFC)

Interleaving of multiple boost converters in PFC circuits is becoming very popular in the recent

applications. The typical interleaved PFC circuit configuration is illustrated in Figure 43-49. The

interleaved PFC operational waveforms is illustrated in Figure 43-50.

By staggering the channels at uniform intervals, multichannel interleaved PFC can reduce the

input current ripple significantly due to ripple cancellation effect. Smaller input current ripple

indicates low Differential Mode (DM) noise filter. It is generally believed that the reduced

differential mode noise magnitude makes the differential mode filter smaller. The output capacitor

voltage ripples are also reduced significantly as a function of the duty cycle.

PWM2H

PWM3H

PWM1L

PWM2L

PWM3L

OUT

Multi-Phase DC/DC Converter