ISL6557 Datasheet, PDF (6/17 Pages) Intersil Corporation – Multi-Phase PWM Controller for Core-Voltage Regulation

ISL6557
COMP
ERROR
+
AMPLIFIER
FB
-
-
+
+
-
DAC
&
REFERENCE
+
-
I_OUT
VDIFF
+
x1
-
RGND
+
-
+
-
+
-
VSEN
PWM
CIRCUIT
PWM
CIRCUIT
PWM
CIRCUIT
AVERAGE
CURRENT
SENSE
CURRENT
SENSE
CURRENT
SENSE
PWM1
VIN
L₁
ISEN1
R_ISEN1
PWM2
VIN
L₂
ISEN2
R_ISEN2
PWM3
VIN
L₃
ISEN3
R_ISEN3
FIGURE 1. SIMPLIFIED BLOCK DIAGRAM OF THE ISL6557 IN A 3-PHASE CONVERTER
V_OUT
C_O
µP
LOAD
Operation
Multi-Phase Power Conversion
Multi-phase power conversion provides the most cost-
effective power solution when load currents are no longer
easily supported by single-phase converters. Although its
greater complexity presents additional technical challenges,
the multi-phase approach offers cost-saving advantages
with improved response time, superior ripple cancellation,
and excellent thermal distribution.
INTERLEAVING
The switching of each channel in a multi-phase converter is
timed to be symmetrically out of phase with each of the other
channels. In a 4-phase converter, each channel switches 1/4
cycle after the previous channel and 1/4 cycle before the
following channel. As a result, the four-phase converter has
a combined ripple frequency four times greater than the
ripple frequency of any one phase. In addition, the peak-to-
peak amplitude of the combined inductor currents is reduced
in proportion to the number of phases (Equations 1 and 2).
Increased ripple frequency and lower ripple amplitude mean
that the designer can use less per-channel inductance and
lower total output capacitance for any performance
specification.
IL1 + IL2 + IL3, 7A/DIV
IL3, 7A/DIV
PWM3, 5V/DIV
IL2, 7A/DIV
IL1, 7A/DIV
PWM2, 5V/DIV
PWM1, 5V/DIV
1µs/DIV
FIGURE 2. PWM AND INDUCTOR-CURRENT WAVEFORMS
FOR 3-PHASE CONVERTER
6