ISL6322 INTERSIL [Intersil Corporation], ISL6322 Datasheet - Page 31

• Manufacturer Part Number: ISL6322
• Description: Four-Phase Buck PWM Controller with Integrated MOSFET Drivers and I2C Interface for Intel VR10, VR11, and AMD Applications
• Manufacturer: INTERSIL [Intersil Corporation]

General Design Guide
This section is intended to provide a high-level explanation of
the steps necessary to create a multiphase power converter. It
is assumed that the reader is familiar with many of the basic
skills and techniques referenced below. In addition to this guide,
Intersil provides complete reference designs that include
schematics, bills of materials, and example board layouts for all
common microprocessor applications.
Power Stages
The first step in designing a multiphase converter is to
determine the number of phases. This determination
depends heavily on the cost analysis, which in turn depends
on system constraints that differ from one design to the next.
Principally, the designer will be concerned with whether
components can be mounted on both sides of the circuit
board, whether through-hole components are permitted, the
total board space available for power-supply circuitry, and
the maximum amount of load current. Generally speaking,
the most economical solutions are those in which each
phase handles between 25A and 30A. All surface-mount
designs will tend toward the lower end of this current range.
If through-hole MOSFETs and inductors can be used, higher
NOTE: It is recommended that frequency shifts occur in 15% increments only.
BIT7
X
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
TABLE 9. REGISTER RGS2 (ADAPTIVE DEADTIME CONTROL/OVERVOLTAGE PROTECTION/SWITCHING FREQUENCY)
BIT6
X
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
BIT5
DT1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
BIT4
DT0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
31
BIT3
OVP
0
0
0
0
0
1
1
1
1
1
0
0
0
0
0
1
1
1
1
1
BIT2
FS2
0
0
0
0
1
0
0
0
0
1
0
0
0
0
1
0
0
0
0
1
BIT1
FS1
0
0
1
1
0
0
0
1
1
0
0
0
1
1
0
0
0
1
1
0
BIT0
FS0
0
1
0
1
0
0
1
0
1
0
0
1
0
1
0
0
1
0
1
0
ADAPTIVE DEADTIME
ISL6322
PHASE DETECT
PHASE DETECT
PHASE DETECT
PHASE DETECT
PHASE DETECT
PHASE DETECT
PHASE DETECT
PHASE DETECT
PHASE DETECT
PHASE DETECT
LGATE DETECT
LGATE DETECT
LGATE DETECT
LGATE DETECT
LGATE DETECT
LGATE DETECT
LGATE DETECT
LGATE DETECT
LGATE DETECT
LGATE DETECT
CONTROL
per-phase currents are possible. In cases where board
space is the limiting constraint, current can be pushed as
high as 40A per phase, but these designs require heat sinks
and forced air to cool the MOSFETs, inductors and heat-
dissipating surfaces.
MOSFETS
The choice of MOSFETs depends on the current each
MOSFET will be required to conduct, the switching frequency,
the capability of the MOSFETs to dissipate heat, and the
availability and nature of heat sinking and air flow.
LOWER MOSFET POWER CALCULATION
The calculation for power loss in the lower MOSFET is
simple, since virtually all of the loss in the lower MOSFET is
due to current conducted through the channel resistance
(r
output current, I
Equation 1), and d is the duty cycle (V
P
DS(ON)
LOW 1
,
). In Equation 23, I
=
r
DS ON
PROTECTION LEVEL
(
OVERVOLTAGE
PP
ALTERNATE
ALTERNATE
ALTERNATE
ALTERNATE
ALTERNATE
ALTERNATE
ALTERNATE
ALTERNATE
ALTERNATE
ALTERNATE
)
DEFAULT
DEFAULT
DEFAULT
DEFAULT
DEFAULT
DEFAULT
DEFAULT
DEFAULT
DEFAULT
DEFAULT
is the peak-to-peak inductor current (see
⋅
⎛
⎜
⎝
I
----- -
N
M
⎞
⎟
⎠
2
⋅
M
(
1 d
is the maximum continuous
–
)
+
I
------------------------------------ -
L PP
,
OUT
2
12
FREQUENCY
⋅
SWITCHING
/V
(
NOMINAL
NOMINAL
NOMINAL
NOMINAL
1 d
IN
+15%
+30%
+15%
+30%
+15%
+30%
+15%
+30%
–
-15%
-30%
-15%
-30%
-15%
-30%
-15%
-30%
).
)
August 21, 2006
(EQ. 23)
FN6328.0