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High Efficiency, High Density Power Supply Delivers 200A
Without Heat Sinks – Design Note 1001
Henry J. Zhang and Wei Chen
Introduction
High speed, high capacity data processing systems are
increasingly hungry for power even as power supply
voltages drop. The result is unprecedented high current
demands, increasing the challenges facing power supply
designers. Power supplies for high end server CPUs must
be capable of supplying more than 100A, they must
respond quickly to fast load transients and they must fit
the same or smaller form factor as previous generation
power supplies.
VIN
xV TO yV
CLKOUT
C5 1000pF
SYNC IN
29
30
31
VOS+
R6 0Ω
32
1
VOS–
2
VDIFFOUT
3
R9 8.06k R10 10k
4
C10 (OPT) C10 (OPT)
5
6
MASTER
ONLY
8
EAIN
9
10
RUN/SS
11
C16 0.01µF
UVADJ
1S1+
1S1–
1S2+
1S2–
1S3–
1S3+
7
12
R13 10Ω
R17 10Ω
TG1
PLLFLTR
FCB
SW1
IN+
BOOST2
IN–
TG2
DIFFOUT
SW2
5V
EAIN
SENSE1+
BG1
SENSE1–
PGND
SENSE2+
BG2
SENSE2–
BG3
SENSE3–
SW3
SENSE3+
TG3
RUN/SS
ITH
BOOST2
PHASMD/PG
C17
1000pF
C19
1000pF
VOUT
VIN
3-PHASE LTC3731CUH
SLAVE BLOCK
VOUT
VIN+
R21
121k
R26 3k
28
C4 0.22µF
27
Q2
Si7892DP
D2
B320A
Q4
Si7860DP
C7
10µF
16V
1S1+
1S1–
C2
1µF
6.3V
25
24
VOS+
C6 0.22µF
23
22
RB 1Ω
21
C8
1µF
16V
20
19
C9
10µF
10V
18
Q5
Si7892DP
17
VOUT+
L2
0.5µH
R12
CDEP105-0R5-H 0.002Ω
D3
B320A
1S2+
1S2–
C12
1µF
6.3V
16
15
14 C14 0.1µF
13
D4
5V
BAT54
Q7
Si7860DP
R14
10Ω
VOS–
C15
10µF
16V
L3
0.5µH
R12
CDEP105-0R5-H 0.002Ω
R18
0Ω
SLAVE
ONLY
R15
10k
PGOOD
Q8
Si7892DP
D5
B320A
MASTER
ONLY
MASTER ONLY
RA (OPT)
5V
ITH
Figure 2. Schematic of the One 3-Phase LTC3731 Block
12/03/1001
J1
VIN+
10V
TO 14V
26
C20
1000pF
C21 3300pF
COUT: 20 PANASONIC
EEFUE0G181R
L1
0.5µH
R11
CDEP105-0R5-H 0.002Ω
C22 100pF
RB (OPT)
DN1001 F01
C1
10µF
16V
R23 10Ω
R24 10Ω
VOUT
0.6V – 1.xV
COUT 200A
DN1001 F02
33
R20
357k
VIN
3-PHASE LTC3731CUH
SLAVE BLOCK
UVADJ
SGND
R19 10Ω
R22 10Ω
BOOST1
PLLIN
VOUT
C114
1µF
6.3V
D1
BAT54A
CLK1
LTC3731CUH
3-PHASE LTC3731CUH
SLAVE BLOCK
Figure 1. Block Diagram of the 12-Phase LTC3731
Synchronous Buck Converter
R4 121k
SLAVE
ONLY
CIN
Q1
Si7860DP
R5 10k C3 0.01µF
VIN
CLK2
30°
CIN: 1 SANYO 16SP270M
+ 18 TAIYO YUDEN
EMK325BJ106M
MASTER
ONLY
R2 374k
VOUT
CLK3
30°
5V
R1 10Ω
3-PHASE LTC3731CUH
MASTER BLOCK
CLK1
30°
,LTC, LT, Burst Mode and PolyPhase are registered trademarks of Linear
Technology Corporation. Stage Shedding is a trademarks of Linear Technology
Corporation.
5V
VIN
1S3+
1S3–
C18
1µF
6.3V
R7
10Ω
J3
VOUT+
E6
VOUT–
Other LTC3731 features include true remote sensing of
the output voltage, adjustable soft start, a wide (4V to
32V) input voltage range, circuit protection features and
two selectable light load operation modes—Stage
SheddingTM mode and Burst Mode® operation to improve
light load efficiency.
12-Phase, 1.5V/200A Supply
Figure 1 shows the block diagram of the 12-Phase, 200A
output supply using four LTC3731 controllers. Figure 2
shows the schematic for a single LTC3731-based 3-phase
circuit block. Each phase uses two SO-8 size MOSFETs to
provide up to 17A of output current. The total footprint of
the power supply fits within a 6.5" × 1.65" area as shown
in Figure 3. The circuit is also low profile—topping out at
5mm including the inductors. The efficiency of this supply
is better than 82% with a 12V input and a 1.5V/200A
output at a 450kHz phase switching frequency. Figure 4
shows supply efficiency over a wide load range, from 20A
to 200A.
Output capacitor requirements are dominated by the total
ESR of the output capacitor network. With twenty low
profile Panasonic S.P. capacitors (180µF/4V) on the output, the maximum output voltage variation during load
transients is within the ±65mVP-P window. In Figure 2,
optional resistors RA and RB can be used to achieve active
voltage positioning (active droop) to further improve the
load transient response or reduce the number of output
capacitors . Please refer to Linear Technology Corporation Design Note 10 for more details on active voltage
positioning.
Conclusion
The LTC3731 can be used to create 3-, 6- or 12-phase
power supplies that provide high current, high density
solutions with good efficiency and rapid transient
response. With state-of-the-art MOSFETs and inductors,
the LTC3731-based 12-phase supply can deliver 250A.
90
VIN = 12V
VOUT = 1.5V
IOUT(MAX) = 200A
89
88
EFFICIENCY (%)
The LTC®3731 3-phase controller helps meet all of these
demands. It is a PolyPhase®, current mode controller that
drives three synchronous buck converters 120° out of
phase at frequencies up to 600kHz per phase. The clock
output and synchronization circuits make it possible to
design 6- or 12-phase buck supplies for very high current
applications. This PolyPhase technique effectively minimizes the number of input and output capacitors and
improves the load transient response. With the LTC3731’s
accurate current sensing, the supply thermal stress is
evenly distributed across all phases. Accurate current
matching also optimizes the size of both output inductors
and MOSFETs. The LTC3731CUH comes in a low profile
5mm × 5mm QFN package with an exposed ground pad
to minimize the thermal impedance.
87
86
85
84
83
82
81
80
0
20 40 60 80 100 120 140 160 180 200
LOAD CURRENT (A)
DN1001 F04
Figure 4. Measured Supply Efficiency vs Output Current
Figure 5 shows a measured load transient waveform. The
load current step is 90A with a slew rate of 150A/µs.
6.5"
1.65"
DN1001 F03
Figure 3. 12-Phase Supply Power Components
Layout and Footprint
Figure 5. Measured Load Transient Response
of the 12-Phase LTC3731 Supply
Data Sheet Download
http://www.linear.com
Linear Technology Corporation
For applications help,
call (408) 432-1900, Ext. 2968
dn1001f LT 1203 • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2003