ISL6559 Intersil Corporation, ISL6559 Datasheet - Page 19

• Manufacturer Part Number: ISL6559
• Description: Multi-Phase PWM Controller
• Manufacturer: Intersil Corporation

and off. Select low ESL ceramic capacitors and place one as
close as possible to each upper MOSFET drain to minimize
board parasitics and maximize suppression.
MULTIPHASE RMS IMPROVEMENT
Figure 18 is provided as a reference to demonstrate the
dramatic reductions in input-capacitor RMS current upon the
implementation of the multiphase topology. For example,
compare the input rms current requirements of a two-phase
converter versus that of a single phase. Assume both
converters have a duty cycle of 0.25, maximum sustained
output current of 40A, and a ratio of I
single phase converter would require 17.3 Arms current
capacity while the two-phase converter would only require 10.9
Arms. The advantages become even more pronounced when
output current is increased and additional phases are added to
keep the component cost down relative to the single phase
approach.
FIGURE 17. NORMALIZED INPUT-CAPACITOR RMS
FIGURE 18. NORMALIZED INPUT-CAPACITOR RMS
0.3
0.2
0.1
0.6
0.4
0.2
0
0
0
0
I
I
C,PP
C,PP
= 0
= 0.25 I
CURRENT VS DUTY CYCLE FOR 4-PHASE
CONVERTER
I
I
I
CURRENT VS DUTY CYCLE FOR SINGLE-PHASE
CONVERTER
C,PP
C,PP
C,PP
0.2
0.2
= 0
= 0.5 I
= 0.75 I
O
DUTY CYCLE (V
DUTY CYCLE (V
O
0.4
O
0.4
19
I
I
C,PP
C,PP
= 0.5 I
= 0.75 I
C,PP
0.6
0.6
IN
IN
/ V
/ V
to I
O
O
O
)
)
O
O
of 0.5. The
0.8
0.8
1.0
1.0
ISL6559
Layout Considerations
The following multi-layer printed circuit board layout strategies
minimize the impact of board parasitics on converter
performance. The following sections highlight some important
practices which should not be overlooked during the layout
process.
Component Placement
Within the allotted implementation area, orient the switching
components first. The switching components are the most
critical because they switch large amounts of energy and
tend to generate large amounts of noise. How the switching
components are placed should also take into account power
dissipation. Align the output inductors and MOSFETs such
that space between the components is minimized while
creating the PHASE plane. Place the Intersil HIP660X
drivers as close as possible to the MOSFETs they control to
reduce the parasitics due to trace length between critical
driver input and output signals. If possible, duplicate the
same placement of these components for each phase.
Next, place the input and output capacitors. Position one
high-frequency ceramic input capacitor next to each upper
MOSFET drain. Place the bulk input capacitors as close to
the upper MOSFET drains as dictated by the component
size and dimensions. Long distances between input
capacitors and MOSFET drains results in too much trace
inductance and a reduction in capacitor performance. Locate
the output capacitors between the inductors and the load,
while keeping them in close proximity around the
microprocessor socket.