3PHASEPWM Datasheet, PDF (4/5 Pages) International Rectifier – 3-Phase Synchronous PWM Controller IC Provides an Integrated Solution for Intel VRM 9.0 Design Guidelines

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 in 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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