an9722

DC-DC Converters for Microprocessors with
Fixed Core Voltage Requirements
TM
Application Note
April 1997
AN9722
Introduction
Intersil HIP6006 and HIP6007
Today’s high-performance microprocessors present many
challenges to their power source. High power consumption,
low bus voltages, and fast load changes are the principal
characteristics which have led to the need for a switch-mode
DC-DC converter local to the microprocessor.
The Intersil HIP6006 and HIP6007 are voltage-mode
controllers with many functions needed for high-performance
processors. Figure 1 shows a simple block diagram of the
HIP6006 and HIP6007. Each contains a high-performance
error amplifier, a high-accuracy reference, a programmable
free-running oscillator, and overcurrent protection circuitry.
The HIP6006 has two MOSFET drivers for use in
synchronous-rectified Buck converters. The HIP6007 omits
the lower MOSFET driver for standard Buck configurations.
A more complete description of the parts can be found in
their data sheets [2, 3].
Intel has specified Voltage Regulator Modules (VRMs) for
the Pentium Pro and Pentium II microprocessors [1]. These
specifications detail the requirements imposed upon the
input power source(s) by the Pentium Pro and Pentium II and
provide the computer industry with standard DC-DC
converter solutions. A common requirement of these and
similar processors are decreasing supply voltages as the
processor clock frequency increases.
The Intersil HIP6002-5 pulse-width modulator (PWM)
controllers are targeted specifically for DC-DC converters
powering the Pentium Pro, Pentium II, and other highperformance microprocessors with varying core voltage
requirements. The HIP6002 and HIP6003 have a 4-bit digital
to analog converter (DAC) and the HIP6004-5 have a 5-bit
DAC to address the ‘moving target’ processor core voltage.
The HIP6006 and HIP6007 use the same basic architecture
of the HIP6002-5, but have a reduced feature set. One
feature removed is the DAC, which allows the HIP6006 and
HIP6007 to be packaged in a smaller 14 lead SOIC. These
chips provide cost-effective solutions for point-of-use switchmode. DC-DC converters for many applications. This
application note details the HIP6006 and HIP6007 in DC-DC
converters for high-performance microprocessors with a
fixed core voltage.
VCC
OCSET
MONITOR AND
PROTECTION
SS
HIP6006/7 Reference Designs
The HIP6006/7EVAL1 is an evaluation board which
highlights the operation of the HIP6006 or the HIP6007 in an
embedded motherboard application. The evaluation board
can be configured as either a synchronous Buck
(HIP6006EVAL1) or standard Buck (HIP6007EVAL1)
converter.
HIP6006EVAL1
The HIP6006EVAL1 is a synchronous Buck converter
capable of providing up to 9A of current at a fixed 2.5V
output voltages. Simple resistor value changes allow for
outputs as low as 1.3V. The schematic and bill-of-materials
for this design can be found in the appendix.
Efficiency
Figure 2 displays the HIP6006EVAL1 efficiency versus load
current for both 5V and 12V inputs with 100 linear feet per
minute (LFM) of airflow. For a given output voltage and load,
the efficiency is lower at higher input voltages. This is due
primarily to higher MOSFET switching losses and is
displayed in Figure 2.
EN
BOOT
RT
OSC
UGATE
HIP6006
PHASE
REF
FB
PVCC
+
-
LGATE
+
PGND
GND
COMP
NOT PRESENT
(PINS NC)
ON HIP6007
FIGURE 1. BLOCK DIAGRAM OF HIP6006 AND HIP6007
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 321-724-7143 | Intersil (and design) is a trademark of Intersil Americas Inc.
Copyright © Intersil Americas Inc. 2001. All Rights Reserved
Pentium® is a registered trademark of Intel Corporation.
Application Note 9722
Transient Response
EFFICIENCY (%)
90
Figure 3 shows a laboratory oscillogram of the
HIP6006EVAL1 in response to a 0-9A load transient
application. The output voltage responds rapidly and is
within 1% of its nominal value in less than 15µs.
VIN = 5V
85
Output Voltage Ripple
VIN = 12V
The output voltage ripple and inductor current of the
HIP6006EVAL1 is shown in Figure 4. The input voltage is 5V
and the load current is 9A for this oscillogram. Peak-to-peak
voltage ripple is about 20mV under these conditions.
80
75
HIP6007EVAL1
2
4
6
LOAD CURRENT (A)
8
FIGURE 2. HIP6006EVAL1 EFFICIENCY vs LOAD
10
The HIP6007EVAL1 is a standard Buck converter capable of
providing up to 9A of current. The schematic and bill-ofmaterials for this design can be found in the appendix. The
HIP6007EVAL1 differs from the HIP6006EVAL1 in four
ways:
1. U1 is a HIP6007
2. CR3 replaces Q2 and CR2
2.50V
3. Jumper JP1 is added
VOUT
50mV/DIV
4. L1 is a larger inductor
COMP
2V/DIV
0V
IL
5A/DIV
JP1 is needed because CR3 is a dual, common-cathode
device and it is replacing a MOSFET. JP1 connects one
device’s anode (the MOSFET gate in the HIP6006EVAL1) to
ground. The other anode and the common cathode replace
the MOSFET source and drain respectively.
Efficiency
Figure 5 shows the efficiency data for the HIP6007EVAL1
under identical conditions as Figure 2 for the
HIP6006EVAL1. Comparing the two graphs reveals that the
Synchronous-Buck design is a little more efficient than the
Standard-Buck design over most of the load range.
0A
TIME (10ms/DIV)
FIGURE 3. HIP6006EVAL1 TRANSIENT RESPONSE
WITH VIN = 12V
VOUT
20mV/DIV
IL
1A/DIV
Transient Response
Figure 6 shows a laboratory oscillogram of the
HIP6007EVAL1 in response to a 0-9A load transient
application. The output voltage responds a little slower than
the HIP6006EVAL1, but still is within 1% of its nominal value
in less than 25ms. Since the HIP6007EVAL1 uses a larger
output inductor and identical control loop compensation (R3,
R5, C14, and C15), the closed-loop gain crossover
frequency is lower than for the HIP6006EVAL1. Check the
Feedback Compensation section of either data sheet for
details on loop compensation design. Table 1 details
simulated closed-loop bandwidth and phase margin for both
reference boards at both +5V and +12V input sources.
TABLE 1. CONTROL LOOP CHARACTERISTICS
HIP6006EVAL1
TIME (1ms/DIV)
FIGURE 4. HIP6006EVAL1 OUTPUT VOLTAGE RIPPLE
2
HIP6007EVAL1
VIN = 5V
VIN = 12V
VIN = 5V
VIN = 12V
f0dB
27KHz
61KHz
12KHz
28KHz
ϕMARGIN
72o
62o
68o
71o
Application Note 9722
OC Protection
Both the HIP6006EVAL1 and HIP6007EVAL1 have lossless
overcurrent (OC) protection. This is accomplished via the
current-sense function of the HIP600x family. The HIP6006
and HIP6007 sense converter load current by monitoring the
drop across the upper MOSFET (Q1 in the schematics). By
selecting the appropriate value of the OCSET resistor (R6),
an overcurrent protection scheme is employed without the
cost and power loss associated with an external currentsense resistor. See the Over-Current Protection section of
either the HIP6006 and HIP6007 data sheet for details on
the design procedure for the OCSET resistor.
90
EFFICIENCY (%)
VIN = 5V
85
VIN = 12V
80
75
2
4
6
LOAD CURRENT (A)
8
10
FIGURE 5. HIP6007EVAL1 EFFICIENCY vs LOAD
VOUT
50mV/DIV
2.50V
COMP
2V/DIV
0V
IL
5A/DIV
Customization of Reference Designs
The HIP6006EVAL1 and HIP6007EVAL1 reference designs
are solutions for Pentium-class microprocessors with current
demands of up to 9A. The two designs share much common
circuitry and the same printed circuit board. Other than the
four items listed under the HIP6007EVAL1 section, one
basic design is employed to meet many different
applications. The evaluation boards can be powered from
+5V or +12V and a standard Buck or a synchronous Buck
topology may be employed. Employing one basic design for
numerous applications involves some trade-offs. These
trade-offs are discussed below to help the user optimize for
a given application.
Control Loop Bandwidth/Transient Response
0A
TIME (10ms/DIV)
FIGURE 6. HIP6007EVAL1 TRANSIENT RESPONSE
WITH VIN = 12V
VOUT
20mV/DIV
IL
1A/DIV
TIME (1µs/DIV)
FIGURE 7. HIP6007EVAL1 OUTPUT VOLTAGE RIPPLE
Output Voltage Ripple
The output voltage ripple and inductor current of the
HIP6007EVAL1 is shown in Figure 7. The input voltage is 5V
and the load current is 9A for this oscillogram. Peak-to-peak
voltage ripple is less than that for the HIP6006EVAL1 (about
15mV), since the output inductor is larger.
3
Table 1 shows how the control loop characteristics vary with
line voltage and topology. The line voltage determines the
amount of DC gain, which directly affects the modulator
(control-to-output) transfer function. The topology (standard
buck or synchronous buck) is important because we have
chosen to use a larger output inductor for the standard buck
(HIP6005) design. This lowers the boundary of continuous
conduction mode (ccm) and discontinuous conduction mode
(dcm) operation. Staying in ccm at light loads can have an
adverse affect on transient response of the converter. The
HIP6006EVAL1 design will not go into dcm operation
because the lower MOSFET conducts current even at light
or zero load conditions.
From Table 1, we see that the highest control loop
bandwidth is the HIP6006EVAL1 with VIN = 12V. The
transient response of the converter for this case is shown in
Figure 3. The other three cases have slower responding
loops and can be improved with value changes in the
compensation components. Table 2 details suggested
changes and the improved control loop characteristics for
the three applications with slower control loops.
Application Note 9722
TABLE 2. MODIFICATIONS TO CONTROL LOOP
HIP6006EVAL1
HIP6007EVAL1
VIN = 5V
VIN = 12V
VIN = 5V
VIN = 12V
R5
30.1K
no change
80.6K
30.1K
C14
no change
no change
10p
no change
f0dB
47kHz
61kHz
44kHz
48kHz
ϕMARGIN
53o
62o
40o
52o
The RFP25N05 (used on the HIP6006/7EVAL1) has a
rDS(ON) equal to 47mΩ (maximum at 25oC) versus 28mΩ
for the RFP45N06. In comparison to the RFP25N05, the
RFP45N06 MOSFETs increased switching losses are
greater than its decreased conduction losses at load
currents up to about 7A with a 5V input and about 9A with a
12V input.
VIN = 5V, RFP25N05
Ripple Voltage
VIN = 5V, RFP45N06
The amount of ripple voltage on the output of the DC-DC
converter varies with input voltage, switching frequency,
output inductor, and output capacitors. For a fixed switching
frequency and output filter, the voltage ripple increases with
higher input voltage. The ripple content of the output voltage
can be estimated with the following simple equation:
EFFICIENCY (%)
90
85
VIN = 12V, RFP25N05
80
VIN = 12V, RFP45N06
75
∆V OUT = ∆IL • ESR
where
2
V OUT
( VIN – VOUT ) • ---------------- • Ts
VIN
∆IL = ----------------------------------------------------------------------L OU T
4
6
LOAD CURRENT (A)
8
10
FIGURE 8. HIP6006EVAL1 EFFICIENCY WITH EITHER
RFP25N05 MOSFETs OR RFP45N06 MOSFETs
ESR = equivalent series resistance of output capacitors
Conclusion
Ts = switching period (1/Fs)
The HIP6006EVAL1 and HIP6007EVAL1 are DC-DC
converters reference designs for microprocessors with fixed
core voltages and current requirements of up to 9A. In
addition, the designs can be modified for applications with
different requirements. The printed circuit board is laid out to
accommodate the necessary components for operation at
currents up to 15A.
LOUT = output inductance
Therefore, for equivalent output ripple performance at VIN =
12V as at 5V, the output filter or switching frequency must
change. Assuming 200KHz operation is desired, either the
output inductor value should increase or the number of
parallel output capacitors should increase (to decrease the
effective ESR).
Increased Output Power Capability
The HIP6006/7EVAL1 printed circuit board is laid out with
flexibility to increase the power level of the DC-DC converter
beyond 9A. Locations for additional input capacitors and
output capacitors are provided. In conjunction with higher
current MOSFETs, Schottky rectifiers, and inductors, the
evaluation board can be tailored for applications requiring
upwards of 15A. The HIP6006 and HIP6007 data sheets’
Component Selection Guidelines sections help the user with
the design issues for these applications. Of course, the
HIP6006/7EVAL1 can be modified for more cost-effective
solutions at lower currents as well.
MOSFET Selection
As a supplement to the data sheets’ application information
on MOSFET Selection Considerations, this section shows
graphically that a larger, lower rDS(ON) MOSFET does not
always improve converter efficiency. Figure 8 shows that
smaller RFP25N05 MOSFETs are more efficient over most
of the line and load range than larger RFP45N06 MOSFETs.
4
References
For Intersil documents available on the web, see
http://www.intersil.com/
[1] Pentium-Pro Processor Power Distribution Guidelines,
Intel Application Note AP-523, November, 1995.
[2] HIP6006 Data Sheet, Intersil Corporation, Doc. No. 4306.
[3] HIP6007 Data Sheet, Intersil Corporation, Doc. No.
4307.
Application Note 9722
12VCC
VIN
C1-3
3 x 680µF
C17-18
2 x 1µF
1206
RTN
C12
1µF
1206
R7
10K
C19
VCC
EN 6
SS 3
ENABLE
CR1
4148
1000pF
14
2 OCSET
MONITOR AND
PROTECTION
R6
3.01k
PHASE
TP2
10 BOOT
RT 1
Q1
C13
0.1µF
U1
R1
SPARE
C14
C15
R5
0.01µF
C16
15K
SPARE
R3
1K
33pF
Q2
12 LGATE
+
11 PGND
4
R2
1K
VOUT
13 PVCC
+
-
FB 5
L1
8 PHASE
HIP6006
REF
C20
0.1µF
9 UGATE
OSC
CR2
MBR
340
C6-9
4 x 1000µF
RTN
7
COMP
GND
JP1
COMP
TP1
R4
SPARE
FIGURE 9. HIP6006EVAL1 SCHEMATIC
12VCC
VIN
C17-18
2 x 1µF
1206
C1-3
3 x 680µF
RTN
C12
1µF
1206
R7
10K
C19
VCC
1000pF
14
ENABLE
EN
6
SS
3
2 OCSET
MONITOR AND
PROTECTION
CR1
4148
R6
3.01k
PHASE
TP2
10 BOOT
RT 1
Q1
C13
0.1µF
U1
R1
SPARE
FB 5
VOUT
13 NC
+
+
-
12 NC
4
R2
1K
L1
8 PHASE
HIP6007
REF
C20
0.1µF
9 UGATE
OSC
7
COMP
C14
CR3
11 NC
GND
RTN
JP1
33pF
C15
0.01µF
R5
COMP
TP1
15K
C16
SPARE
R3
1K
R4
SPARE
FIGURE 10. HIP6007EVAL1 SCHEMATIC
5
C6-9
4 x 1000µF
Application Note 9722
Bill of Materials for HIP6006EVAL1
PART NUMBER
DESCRIPTION
PACKAGE
QTY
REF
VENDOR
25MV680GX
680µF, 25V Aluminum Capacitor
Radial 10 x 22
3
C1 - C3
Sanyo
6MV1000GX
1000µF, 6.3V Aluminum Capacitor
Radial 8 x 20
4
C6 - C9
Sanyo
1206YZ105MAT1A
1.0µF, 16V, X7S Ceramic Capacitor
1206
3
C12, C17-C18
AVX
1000pF Ceramic
1nF, X7R Ceramic Capacitor
0805
1
C19
Various
0.1uF Ceramic
0.1µF, 25V X7R Ceramic Capacitor
0805
2
C13, C20
AVX/Panasonic
0.01uF Ceramic
0.01µF, X7R Ceramic Capacitor
0805
1
C15
Various
33pF Ceramic
33pF, X7R Ceramic Capacitor
0805
1
C14
Various
Spare
Spare Ceramic Capacitor
0805
1N4148
Rectifier 75V
DO35
1
CR1
Various
MBR340
3A, 40V, Schottky
Axial
1
CR2
Motorola
CTX09-13313-X1
PO343
5.3µH, 12A Inductor
T50-52B Core, 10 Turns of 16 AWG Wire
Wound Toroid
1
L1
Coiltronics
Pulse
RFP25N05
47mΩ, 50V MOSFET
TO220
2
Q1, Q2
Intersil
HIP6006
Synchronous Rectified Buck Controller
SOIC-14
1
U1
Intersil
10kΩ
10kΩ, 5% 0.1W, Resistor
0805
1
R7
Various
Spare
Spare 0.1W, Resistor
0805
15kΩ
15kΩ, 5%, 0.1W, Resistor
0805
1
R5
Various
1kΩ
1kΩ, 5%, 0.1W, Resistor
0805
2
R2-R3
Various
3.01kΩ
3.01kΩ, 1%, 0.1W, Resistor
0805
1
R6
Various
576802B00000
TO-220 Clip-on Heatsink
2
1514-2
Terminal Post
6
VIN, 12VCC,
VOUT, RTN
Keystone
1314353-00
Scope Probe Test Point
1
V OUT
Tektronics
SPCJ-123-01
Test Point
3
ENABLE, TP1,
TP2
Jolo
6
C16
R1,R4
AAVID
Application Note 9722
Bill of Materials for HIP6007EVAL1
PART NUMBER
DESCRIPTION
PACKAGE
QTY
REF
VENDOR
Radial 10 x 22
3
C1 - C3
Sanyo
Radial 8 x 20
4
C6 - C9
Sanyo
25MV680GX
680µF, 25V Aluminum Capacitor
6MV1000GX
1000µF, 6.3V Aluminum Capacitor
1206YZ105MAT1A
1.0µF, 16V, X7S Ceramic Capacitor
1206
3
C12, C17-C18
AVX
1000pF Ceramic
1nF, X7R Ceramic Capacitor
0805
1
C19
Various
0.1µF Ceramic
0.1µF, 25 V X7R Ceramic Capacitor
0805
2
C13, C20
AVX/Panasonic
0.01µF Ceramic
0.01µF, X7R Ceramic Capacitor
0805
1
C15
Various
33pF Ceramic
33pF, X7R Ceramic Capacitor
0805
1
C14
Various
Spare
Spare Ceramic Capacitor
0805
1N4148
Rectifier 75V
DO35
1
CR1
Various
MBR1535CT
15A, 35V, Schottky
TO220
1
CR3
Motorola
CTX09-13337-X1
PO345
7µH, 12A Inductor
T60-52 Core, 14 turns of 17 AWG wire
Wound Toroid
1
L1
Coiltronics
Pulse
RFP25N05
47mΩ, 50V MOSFET
TO220
1
Q1
Intersil
HIP6007
Synchronous Rectified Buck Controller
SOIC-14
1
U1
Intersil
10kΩ
10kΩ, 5%, 0.1W, Resistor
0805
1
R7
Various
Spare
Spare 0.1W, Resistor
0805
15kΩ
15kΩ, 5%, 0.1W, Resistor
0805
1
R5
Various
1kΩ
1kΩ, 5%, 0.1W, Resistor
0805
2
R2-R3
Various
3.01kΩ
3.01kΩ, 1%, 0.1W, Resistor
0805
1
R6
Various
576802B00000
TO-220 Clip-on Heatsink
2
1514-2
Terminal Post
6
V IN, 12VCC,
VOUT, RTN
Keystone
1314353-00
Scope Probe Test Point
1
VOUT
Tektronics
SPCJ-123-01
Test Point
3
ENABLE, TP1,
TP2
Jolo
7
C16
R1, R4
AAVID
Application Note 9722
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.
Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without
notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and
reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result
from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see www.intersil.com
8
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