3PHASEPWM datasheet(4/5 Pages) IRF

4 / 5 page

Operation of IRU3055

PWM Signal

The 3-phase oscillator provides a constant

frequency up to 500kHz/phase, programmable

by external resistor. The three PWMs ramp

signals with 120 degree phase shift. The three

comparators and three PWM latches will

generate three PWM outputs to the drivers,

which are built inside the IC. A typical 3-phase

PWM signal is shown in Figure 2.

Figure 2 - The 3-phase PWM signal

Voltage and Current Loop

IRU3055 has three transconductance error

amplifiers. The master Error amplifier is used to

regulate the output voltage. The output voltage

can connect directly, or through a resistor

divider, to the Fb pin of the error amplifier. The

compensation network at the output of the

amplifier (Comp Pin) helps to stabilize the

voltage loop. The non-inverting pin of the

master amplifier is connected to the output of

the

DAC,

which

interfaces

with

the

microprocessor core and determines the desired

output voltage. Two additional transconductance

amplifiers are used to balance the output

inductor current among 3-phases.

Output Current Ripple Reduction

One of advantages of multiphase converters is

that the output current ripple is significantly

reduced. The current ripple from multiple

converters tend to cancel each other so that the

total output current ripple flowing into the

output capacitor is reduced. In this case, the

output

inductor

each

individual

buck

converter can be selected smaller to improve the

load transient response without increasing the

output current ripple. Figure 3 shows a 3-phase

inductor current and current ripple in the

capacitor for 12V input 1.5V, 50A, 3-phase buck

converter. The effective output ripple has three

times

frequency

and

smaller

amplitude

compared with each individual converter. Figure

4 indicates the total ripple current, as a function

of duty cycle, normalized to the parameter

Vo/(L*Fs) at zero duty cycle.

Figure 3- Output inductor currents and output

capacitor ripple current.

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