ISL6569 Datasheet, PDF (8/22 Pages) Intersil Corporation – Multi-Phase PWM Controller

ISL6569
OFS
x0.1
100µA
COMP
+
-
REFERENCE
&
DAC
+
-
+
FB
-
ERROR
AMPLIFIER
IOUT
I_OUT
+
-
VDIFF
-
x1
+
+
-
PWM
CIRCUIT
PWM
CIRCUIT
AVERAGE
CURRENT
SENSE
CURRENT
SENSE
PWM1
VIN
L₁
ISEN1
R_ISEN1
PWM2
V_OUT
µP
C_O
LOAD
VIN
L₂
ISEN2
R_ISEN2
VSEN
RGND
FIGURE 1. SIMPLIFIED BLOCK DIAGRAM OF A ISL6569 CONVERTER
Interleaving
The switching of each channel in a multi-phase converter is
timed to be symmetrically out of phase with the other
channel. In a 2-phase converter, channel-2 switches half a
cycle after channel-1. As a result, the converter has a ripple
frequency twice that of either phase. Figure 2 illustrates the
multiplicative effect on output ripple frequency. The two
channel currents (IL1and IL2), combine to form the AC ripple
current and the DC load current. The ripple component has
twice the ripple frequency of either channel current. Each
PWM pulse is terminated half of a cycle, or 2.0µs, after the
PWM pulse of the previous phase. The peak-to-peak current
waveform for each phase is about 7A, and the dc components
of the inductor currents combine to feed the load.
IL1 + IL2, 7A/DIV
IL2, 7A/DIV
PWM2, 5V/DIV
IL1, 7A/DIV
PWM1, 5V/DIV
1µs/DIV
FIGURE 2. PWM AND INDUCTOR-CURRENT WAVEFORMS
FOR 2-PHASE CONVERTER
In addition, the peak-to-peak amplitude of the combined
inductor currents is reduced in proportion to the number of
phases. To understand the reduction of ripple current
amplitude in the multi-phase circuit, examine the equation
8
FN9085.7
December 29, 2004