ISL6334AIRZR5368 Intersil, ISL6334AIRZR5368 Datasheet - Page 29

• Manufacturer Part Number: ISL6334AIRZR5368
• Description: IC CTRLR PWM 4PHASE BUCK 40QFN
• Manufacturer: Intersil

Specifications of ISL6334AIRZR5368

• Applications: Controller, Intel VR11.1
• Voltage - Input: 3 V ~ 12 V
• Number Of Outputs: 1
• Voltage - Output: 0.5 V ~ 1.6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: *
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

For a 2-phase design, use Figure 18 to determine the input-
capacitor RMS current requirement given the duty cycle,
maximum sustained output current (I
per-phase peak-to-peak inductor current (I
Select a bulk capacitor with a ripple current rating which will
minimize the total number of input capacitors required to
support the RMS current calculated. The voltage rating of
the capacitors should also be at least 1.25 times greater
than the maximum input voltage.
Figures 19 and 20 provide the same input RMS current
information for three and four phase designs respectively.
Use the same approach to selecting the bulk capacitor type
and number as previously described.
Low capacitance, high-frequency ceramic capacitors are
needed in addition to the bulk capacitors to suppress leading
and falling edge voltage spikes. The result from the high
current slew rates produced by the upper MOSFETs turn on
and off. Select low ESL ceramic capacitors and place one as
close as possible to each upper MOSFET drain to minimize
board parasitic impedances and maximize suppression.
FIGURE 19. NORMALIZED INPUT-CAPACITOR RMS CURRENT
FIGURE 20. NORMALIZED INPUT-CAPACITOR RMS CURRENT
0.3
0.2
0.1
0.3
0.2
0.1
0
0
0
0
I
I
I
I
L(P-P)
L(P-P)
L(P-P)
L(P-P)
vs DUTY CYCLE FOR 3-PHASE CONVERTER
vs DUTY CYCLE FOR 4-PHASE CONVERTER
= 0
= 0.25 I
= 0
= 0.25 I
0.2
0.2
O
O
DUTY CYCLE (V
DUTY CYCLE (V
0.4
0.4
29
I
I
I
I
L(P-P)
L(P-P)
L(P-P)
L(P-P)
= 0.5 I
= 0.75 I
0.6
= 0.5 I
= 0.75 I
0.6
O/
O/
O
V
V
), and the ratio of the
IN
IN
O
O
)
)
O
O
L(P-P)
0.8
0.8
) to I
O
1.0
ISL6334AR5368
1.0
.
MULTIPHASE RMS IMPROVEMENT
Figure 21 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 2-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 17.3A
capacity while the two-phase converter would only require
10.9A
when output current is increased and additional phases are
added to keep the component cost down relative to the
single phase approach.
Layout Considerations
The following layout strategies are intended to minimize the
impact of board parasitic impedances on converter
performance and to optimize the heat-dissipating capabilities
of the printed-circuit board. These 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 carry large amounts of energy and tend
to generate high levels of noise. Switching component
placement should 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 MOSFET driver IC as close as
possible to the MOSFETs they control to reduce the parasitic
impedances due to trace length between critical driver input
and output signals. If possible, duplicate the same placement
of these components for each phase.
FIGURE 21. NORMALIZED INPUT-CAPACITOR RMS
RMS
0.6
0.4
0.2
0
0
. The advantages become even more pronounced
CURRENT vs DUTY CYCLE FOR SINGLE-PHASE
CONVERTER
I
I
I
L(P-P)
L(P-P)
L(P-P)
0.2
= 0
= 0.5 I
= 0.75 I
DUTY CYCLE (V
O
0.4
O
0.6
O/
L,PP
V
IN
)
to I
RMS
0.8
O
September 7, 2010
of 0.5. The
current
1.0
FN6839.2