ISL6322_14 Datasheet, PDF (31/41 Pages) Intersil Corporation – Four-Phase Buck PWM Controller with Integrated MOSFET Drivers and I2C Interface for Intel VR10, VR11, and AMD Applications

ISL6322
TABLE 9. REGISTER RGS2 (ADAPTIVE DEADTIME CONTROL/OVERVOLTAGE PROTECTION/SWITCHING FREQUENCY)
BIT7 BIT6 BIT5 BIT4 BIT3 BIT2 BIT1 BIT0
ADAPTIVE DEADTIME
X
X DT1 DT0 OVP FS2 FS1 FS0
CONTROL
OVERVOLTAGE
PROTECTION LEVEL
SWITCHING
FREQUENCY
x
x
0
0
0
0
0
0
PHASE DETECT
DEFAULT
NOMINAL
x
x
0
0
0
0
0
1
PHASE DETECT
DEFAULT
-15%
x
x
0
0
0
0
1
0
PHASE DETECT
DEFAULT
-30%
x
x
0
0
0
0
1
1
PHASE DETECT
DEFAULT
+15%
x
x
0
0
0
1
0
0
PHASE DETECT
DEFAULT
+30%
x
x
0
0
1
0
0
0
PHASE DETECT
ALTERNATE
NOMINAL
x
x
0
0
1
0
0
1
PHASE DETECT
ALTERNATE
-15%
x
x
0
0
1
0
1
0
PHASE DETECT
ALTERNATE
-30%
x
x
0
0
1
0
1
1
PHASE DETECT
ALTERNATE
+15%
x
x
0
0
1
1
0
0
PHASE DETECT
ALTERNATE
+30%
x
x
0
1
0
0
0
0
LGATE DETECT
DEFAULT
NOMINAL
x
x
0
1
0
0
0
1
LGATE DETECT
DEFAULT
-15%
x
x
0
1
0
0
1
0
LGATE DETECT
DEFAULT
-30%
x
x
0
1
0
0
1
1
LGATE DETECT
DEFAULT
+15%
x
x
0
1
0
1
0
0
LGATE DETECT
DEFAULT
+30%
x
x
0
1
1
0
0
0
LGATE DETECT
ALTERNATE
NOMINAL
x
x
0
1
1
0
0
1
LGATE DETECT
ALTERNATE
-15%
x
x
0
1
1
0
1
0
LGATE DETECT
ALTERNATE
-30%
x
x
0
1
1
0
1
1
LGATE DETECT
ALTERNATE
+15%
x
x
0
1
1
1
0
0
LGATE DETECT
ALTERNATE
+30%
NOTE: It is recommended that frequency shifts occur in 15% increments only.
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
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_DS(ON)). In Equation 23, I_M is the maximum continuous
output current, I_PP is the peak-to-peak inductor current (see
Equation 1), and d is the duty cycle (V_OUT/V_IN).
P_{LOW, 1} = r_DS(ON) ⋅
⎛
⎜
⎝
I--_{M---⎟⎞}
N⎠
2
⋅
(
1
–
d
)
+
I--_L---,---^2P_----P-----⋅_---(_--1-----–_-----d----)
12
(EQ. 23)
31
FN6328.2
August 2, 2007