an9672

A Voltage Regulator Module (VRM) Using the
HIP6004 PWM Controller (HIP6004EVAL1)
®
Application Note
January 1997
AN9672
Author: Greg J. Miller
Introduction
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.
Intel has specified a Voltage Regulator Module (VRM) for
the Pentium Pro Microprocessor [1]. This specification
details the requirements imposed upon the input power
source(s) by the Pentium-Pro and provides the computer
industry with a standard DC-DC converter solution. The
Intersil HIP6002 and HIP6003 pulse-width modulator (PWM)
controllers are targeted specifically for DC-DC converters
powering the Pentium-Pro and similar high-performance
microprocessors. The HIP6004 and HIP6005 PWM
controllers are enhanced versions of the HIP6002 and
HIP6003, with additional features specifically for nextgeneration microprocessors.
Intersil HIP6004
Figure 1 shows a simple block diagram of the HIP6004. The
HIP6004 is the controller for a synchronous-rectified Buck
converter. It contains a high-performance error amplifier, a
high-resolution 5-bit digital-to-analog converter (DAC), a
programmable free-running oscillator, and a pair of N-Channel
MOSFET drivers. A more complete description of the part can
be found in the HIP6004 Data Sheet [2]. The HIP6005 is very
similar to the HIP6004, but is targeted for standard buck
converters.
PGOOD 12
VID0
VID1
VID2
VID3
VID4
FB
20
4
5
6
7
8
10
OVP
18
19
• Overcurrent Protection
Input Voltage Sources
The HIP6004EVAL1 VRM is able to run off either +5VDC or
+12VDC main power source. In either case, +12V is
required for the bias supply of the HIP6004. The
HIP6004EVAL1 is configured to accept a 5V source, as
shown in Figure 2. The three approaches for powering the
VRM from +12V are:
1. Increase +5V source to +12V (for lab evaluation).
2. Tie 12Vin pins to 5Vin pins (again, lab evaluation).
3. Move F1 fuse as shown in Figure 2 and apply +12Vin (for
system implementation).
FUSE LOCATION 1: 5V SOURCE
FIGURE 2. INPUT FUSE LOCATION vs INPUT SOURCE VOLTAGE
1 VSEN
Output Voltage
The output voltage of the VRM is set by the 5-bit code
(VID0 - VID4) programmed by the processor in the system.
The DAC internal to the HIP6004 adjusts the internal
reference to set the nominal converter output voltage. The
output voltage programming is defined in the HIP6004 Data
Sheet.
17 LGATE
-
+
16 PGND
11
GND
FIGURE 1. BLOCK DIAGRAM OF HIP6004
HIP6004EVAL1 Reference Design
The HIP6004EVAL1 is an evaluation board which highlights
the operation of the HIP6004 in an expanded version of the
Pentium-Pro VRM. This evaluation board has greater
voltage adjustability (1.3V - 3.5V) and higher output current
capability (up to 14A) than the Intel-specified Pentium-Pro
1
• Overvoltage Protection via SCR and Fuse
F1
13 PHASE
D/A
COMP
• 5-Bit DAC with ±1% Accuracy
F1
14 UGATE
9
• Operates in +5V or +12V Input Systems
15 BOOT
HIP6004
-
• Exceeds Intel Pentium-Pro VRM Specifications
- Form-Factor (3.1” x 1.5” x 1.1”)
- Efficiency
- Regulation
FUSE LOCATION 2: 12V SOURCE
OSC
+
HIP6004EVAL1 Features
2 OCSET
MONITOR
AND
PROTECTION
SS 3
RT
VCC
VRM. Intersil also offers a Pentium-Pro VRM evaluation
board, the HIP6003EVAL1 [3].
The HIP6004EVAL1 is a solution for many different
microprocessors, both present and future. It is capable of
supplying greater than 14A of current and provide output
voltages from 1.3V to 3.5V.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Pentium® is a registered trademark of Intel Corporation.
Application Note 9672
Efficiency
It does spread the main switch power losses across three
devices so it does have some thermal advantages. Similar
results can be expected for the comparison of two versus
three lower MOSFETs when Vin = 12V.
Figure 3 shows the measured evaluation board efficiency
versus load current for four different conditions. The data
was taken at room temperature with 100 linear feet per
minute (LFM) of airflow.
Thermal Performance
The thermal performance of the VRM is shown in Figure 5.
This data is with the following conditions applied:
EFFICIENCY (%)
95
90
1. VIN = 5V and VOUT = 2.8V.
85
2. 100 linear feet per minute (LFM) airflow parallel to the
plane of the pc board.
3. Ambient temperature = 22oC.
VIN = 5V, VOUT = 2.8V
VIN = 5V, VOUT = 2.0V
VIN = 12V, VOUT = 2.8V
VIN = 12V, VOUT= 2.0V
80
75
70
65
2
4
6
8
10
12
14
LOAD CURRENT (A)
FIGURE 3. EFFICIENCY vs LOAD FOR HIP6004EVAL1
Thermal considerations were a major influence on the
design of the HIP6004EVAL1. The use of surface-mount
SO-8 MOSFETs means that the pc board traces are also the
heat sink. This causes a temperature rise (ΔT) to the pc
board, as evidenced in Figure 5. A four-layer board is used
to help keep the temperature gradients from exceeding
desirable limits. At a 14A load, the pc board ΔT is only about
20oC (measured near the MOSFETs) and the HIP6004
junction temperature is about 67oC.
70
95
HIP6004 JUNCTION
60
TEMPERATURE (oC)
EFFICIENCY (%)
90
2 UPPER MOSFETs
3 UPPER MOSFETs
85
80
75
Q1 (UPPER) JUNCTION
50
40
Q5 (LOWER) JUNCTION
PC BOARD
30
70
20
65
2
4
6
8
LOAD CURRENT (A)
10
12
14
FIGURE 4. COMPARISON OF HIP6004EVAL1 EFFICIENCY
WITH 2 UPPER MOSFETs AND 3 UPPER MOSFETs
The HIP6004EVAL1 uses four Intersil RF1K49157 (30V,
30mΩ) MOSFETs, two in parallel for both the main (upper)
and synchronous (lower) switches. The board was layed out
with provisions for three upper and four lower MOSFETs to
allow for greater flexibility in meeting a variety of
requirements. However, Figure 3 shows that the VRM
provides high efficiency for four different input and output
voltage combinations with only two upper and two lower
MOSFETs.
Figure 4 compares the efficiency of the HIP6004EVAL1,
both with and without an additional upper MOSFET (Q3)
populated at Vin = 5V and Vout = 2.8V. This figure shows
that a third upper MOSFET has minimal impact on efficiency.
2
2
4
8
6
LOAD CURRENT (A)
10
12
14
FIGURE 5. THERMAL PERFORMANCE vs LOAD FOR
HIP6004EVAL1
Transient Response
Figures 6 and 7 show laboratory oscillograms of the
HIP6004EVAL1 in response to a load transient application.
The load transient applied was from 0A to 14A. As Figure 6
shows, the output voltage of the VRM (VOUT) remains well
within the ±5% regulation window. There is sufficient
headroom to allow for worst-case component tolerances
(mainly in the equivalent series resistance (ESR) of the
output capacitors) and temperature effects. Figure 7 details
the positive edge of the load transient application. The
bottom trace is the output inductor current (IL).
Application Note 9672
3.00V
IL (2A/DIV)
14A
+5% REGULATION LIMIT
12A
2.90V
VOUT
10A
2.80V
VOUT (20mV/DIV)
2.70V
-5% REGULATION LIMIT
2.60V
TIME (2ms/DIV)
FIGURE 6. HIP6004EVAL1 OUTPUT TRANSIENT RESPONSE
TIME (2.5μs/DIV)
FIGURE 8. OUTPUT VOLTAGE AND INDUCTOR CURRENT
RIPPLE WITH VIN = 5V, VOUT = 2.8V, AND A 12A
LOAD CURRENT
Output Voltage Droop with Load
2.85V
VOUT
2.80V
2.75V
15A
10A
IL
5A
0A
TIME (50μs/DIV)
The HIP6004EVAL1 uses a droop function to maintain
output voltage regulation through load transients with fewer
(or less costly) output capacitors. With a high di/dt load
transient typical of the Pentium-Pro microprocessor, the
largest deviation of the output voltage is at the leading edge
of the transient. The droop function adds a deviation as a
function of load that counters the transient deviation.
Figure 9 illustrates the static-load droop characteristic. With
no-load, the output voltage is above the nominal output
level. The output decreases (or droops) as the load
increases.
Output Voltage Ripple
The HIP6004EVAL1 has ten parallel output capacitors,
mainly to supply the energy during the severe load
transients imposed by high-performance microprocessors.
This also helps provide a very low output voltage ripple, as
shown in Figure 8. With approximately 2A peak-to-peak (pp) inductor ripple current, the output voltage ripple is only
about 12mVP-P . Including noise spikes, the total output
deviation with this 12ADC load is about 20mVP-P
(measurement is taken with a 20MHz oscilloscope
bandwidth).
If the application does not have a highly dynamic load, then
the number of output capacitors may be reduced. The output
voltage ripple increases with fewer output capacitors. For
instance, with just five output capacitors in parallel, the
output voltage ripple doubles to approximately 24mVP-P .
3
OUTPUT VOLTAGE (V)
FIGURE 7. 0A TO 14A TRANSIENT RESPONSE
2.85
WITHOUT DROOP
2.80
2.75
WITH DROOP
0
5
10
15
OUTPUT CURRENT (A)
FIGURE 9. STATIC REGULATION OF THE HIP6004EVAL1
With a dynamic load, the droop function pre-biases the
output voltage to minimize the total deviation. Prior to the
application of load, the output voltage is above the nominal
level and the transient deviation results in an output lower
than the nominal level. Figure 6 illustrates the droop function
performance on the HIP6004EVAL1 converter. The transient
deviation is approximately 130mV. At light load, the output
voltage is about 50mV higher than the nominal output
voltage of 2.8V. At full load, the output voltage is about
40mV lower than nominal. The total deviation is within
Application Note 9672
±80mV with the droop function compared to a deviation of
over ±130mV without this function. Since the voltage
excursions at the transient edges are mainly a function of the
output capacitors, the converter uses fewer capacitors.
The HIP6004EVAL1 implements the droop function by using
the average voltage drop across the output inductor. The
average voltage drop equals the DC output current times the
DC winding resistance of the output inductor. Instead of
straight voltage feedback, an averaging filter (R8, R9, and
C25 in the schematic) is added around the output inductor.
This filter communicates both the output voltage and droop
information back to the PWM controller. A resistor (R2)
increases the light-load voltage above the DAC program level.
OC Protection
The HIP6004EVAL1 has lossless overcurrent (OC)
protection. This is accomplished via the HIP6004 currentsense function. The HIP6004 senses converter load current
by monitoring the drop across the upper MOSFETs (Q1-2).
By selecting the appropriate value of the OCSET resistor
(R7), an overcurrent protection scheme is employed without
the cost and power loss associated with an external currentsense resistor. The HIP6004 Data Sheet details the design
procedure for the OCSET resistor.
OV Protection
The HIP6004EVAL1 contains circuitry to protect against
overvoltage conditions. In the case of an overvoltage
(greater than 15% over the nominal Vout), the HIP6004 fires
an SCR (Q8) and the input fuse will open.
For applications where this feature is not necessary, the
following components may be eliminated: F1, Q8, and R6. A
wire must replace F1 when using HIP6004EVAL1 without
OV protection.
4
Conclusion
The HIP6004EVAL1 is a reference design suitable for a
DC-DC converter solution for the Pentium-Pro and other
high-performance microprocessors.
References
For Intersil documents available on the internet, see web site
http://www.intersil.com.
[1] Pentium-Pro Processor Power Distribution Guidelines,
Intel Application Note AP-523, November, 1995.
[2] HIP6004 Data Sheet, Intersil Corporation, FN4275.
[3] AN9664 Application Note, Intersil Corporation,
“A Pentium Pro Voltage Regulator Module (VRM) Using
the HIP6003 PWM Controller (HIP6003EVAL1)”
Application Note 9672
Appendix
Board Description
SILK SCREEN - TOP
GND
COMPONENT SIDE
SOLDER SIDE
INTERNAL ONE
SILK SCREEN - BOTTOM
5
Application Note 9672
Schematic Diagram
+12VIN
L1
F1
+5VIN
1.5μH
Q8
2N6394
C1-5
5x 330μF
C21-22
2x 1μF
R6
10K
C17
1μF
1N4148
RT 20
R1
SPARE
VID0
VID1
VID2
VID3
VID4
VCC
OVP
18
19
4
5
6
7
8
U1
HIP6004
PWRGD
1K
Q1-2
-
COMP
C18
2200pF
R4
20
16 PGND
11
GND
Q4-5
C6-15
10x
1000μF
CR2
R8
20K
R9
15K
C25
0.1μF
6
VOUT
3μH
R5
20K
8200pF
17 LGATE
+
-
C24
0.1μF
L2
1 VSEN
+
C20
0.082μF
1000p
R7
13 PHASE
D/A
R2
499K
C23
15 BOOT
14 UGATE
9
R3
1K
12 PGOOD
OSC
FB 10
C19
2 OCSET
MONITOR AND
PROTECTION
SS 3
C16
0.1μF
CR1
Application Note 9672
Bill of Materials
REFERENCE
DESIGNATION
PART NUMBER
DESCRIPTION
MECHANICAL
VENDOR
U1
HIP6004
PWM Controller
SOIC-20
Intersil
Q1-2, 4-5
RF1K49157
MOSFET, 30V, 30mΩ
SOIC-8
Intersil
Q8
2N6394
SCR, 50V, 12A
TO-220
Motorola
CR1
1N4148
Rectifier, 75V
DL-35
CR2
MBRS340T3
Rectifier, Schottky, 40V, 3A
DO-214AB
Motorola
L1
CTX09-13336-X1
PO344
Inductor, 1.5μH
T44-52 Core, 7 Turns of 18 AWG
Thru-Hole
Coiltronics
Pulse
L2
CTX09-13313-X1
PO343
Inductor, 3μH
T50-52B Core, 10 Turns of 16 AWG
Thru-Hole
Coiltronics
Pulse
C1-5
25MV330GX
Capacitor, Al-Elec, 330μF, 25V
Radial, 8 x 20 mm
Sanyo
C6-15
6MV1000GX
EEUFA1A102
Capacitor, Al-Elec, 1000μF, 6.3V
Capacitor, Al-Elec, 1000μF, 10V
Radial, 8 x 20 mm
Radial, 8 x 20 mm
Sanyo
Panasonic
C16, 24-25
Capacitor, Ceramic, 0.1μF, X7R
0805
C18
Capacitor, Ceramic, 2200pF, X7R
0805
C19
Capacitor, Ceramic, 8200pF, X7R
0805
C20
Capacitor, Ceramic, 0.082μF, Z5U
0805
C23
Capacitor, Ceramic, 1000pF, X7R
0805
C17, 21-22
Capacitor, Ceramic, 1μF, Y5V
1206
R2
Resistor, 499K, 1%
0805
R3,7
Resistor, 1K, 1%
0805
R4
Resistor, 20, 5%
0805
R5, 8
Resistor, 20K, 5%
0805
R6
Resistor, 10K, 5%
0805
R9
Resistor, 15K, 5%
0805
251015A
Fuse, 15A
Axial
532956-7
Connector
F1
Littlefuse
Amp
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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
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