DN489 - High Efficiency, High Density 3-Phase Supply Delivers 60A with Power Saving Stage Shedding, Active Voltage Positioning and Nonlinear Control for Superior Load Step Response

High Efficiency, High Density 3-Phase Supply Delivers 60A with
Power Saving Stage Shedding, Active Voltage Positioning
and Nonlinear Control for Superior Load Step Response
Design Note 489
Jian Li and Kerry Holliday
Introduction
The LTC ®3829 is a feature-rich single output 3-phase
synchronous buck controller that meets the power density demands of modern high speed, high capacity data
processing systems, telecom systems, industrial equipment and DC power distribution systems. The LTC3829’s
features include:
• 4.5V to 38V input range and 0.6V to 5V output range
• 3-phase operation for low input current ripple and
output voltage ripple with Stage Shedding™ mode to
yield high light load efficiency
• On-chip drivers in a 38-pin 5mm × 7mm QFN (or 38-pin
FE) package to satisfy demanding space requirements
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered
trademarks and Stage Shedding is a trademark of Linear Technology Corporation. All
other trademarks are the property of their respective owners.
VIN
VIN
10μF
16V
X5R
2.2Ω
VIN
100k
0.1μF
DIFFOUT
30.1k
13.5k
13
14
40.2k
15
VOSENSE
–
1
VOSENSE
+
2
0Ω
66.5Ω DIFFOUT
EXTVCC
PGOOD
ITEMP
38
4
23
17
37
39
9
RUN
IFAST
MODE
ILIM
VIN
INTVCC
VFB
BOOST1
ITH
ISET
TG1
DIFFN
SW1
DIFFP
BG1
DIFFOUT
BOOST2
EXTVCC
PGOOD
TG2
ITEMP
SW2
GND
BG2
BOOST3
TK/SS
5
C21
1000pF
6
7
C22
1000pF
4.7μF
16V
Q1
L1
0.33μH
D1 CMDSH-3
Q3
Q4
8 11
C23
1000pF
TG3
SW3
BG3
S1P
180μF
16V
S1N
25
RSENSE1
0.001Ω
24
33
32
0.1μF
SW1
30
BG1
0.1μF
10μF
16V
X5R
Q1,Q5,Q9: RJK0305DPB
Q3,Q4,Q7,Q8,Q11,Q12: RJK0330DPB
TG2
28
SW2
29
BG2
VOSENSE+
Q5
D3 CMDSH-3
L2
0.33μH
S2P
S2N
VOUT
19
20
330μF
2.5V
SANYO
w2
+
VIN
26
27
100μF
6.3V
X5R
TG1
31
D2 CMDSH-3
LTC3829
AVP
SENSE1+
CSS
0.1μF
CLKOUT
VIN
7V TO 14V
+
GND
36
SENSE3+
1nF
34
SENSE2–
CLKOUT
PLLIN
47pF
SENSE1–
SENSE2+
20.0k
FREQ
18 16 10 35 3
180μF
16V
INTVCC
PLLIN
SENSE3–
100pF
MODE
RUN
40.2k
+
0.1μF
Q7
RSENSE2
0.001Ω
Q8
10Ω
330μF
2.5V
SANYO
w2
100μF
6.3V
X5R
21
+
22
VIN
12
10Ω
10μF
16V
X5R
R26 100Ω
S3N
VOSENSE
–
R25 100Ω
S3P
TG3
R24 100Ω
S2N
R23 100Ω
Q9
L3
0.33μH
Q11
Q12
SW3
S2P
S3P
R22 100Ω
S1N
R21 100Ω
BG3
S1P
S3N
RSENSE3
0.001Ω
100μF
6.3V
X5R
+
330μF
2.5V
SANYO
w2
DN489 F01
Figure 1. A 1.5V/60A 3-Phase Converter Featuring the LTC3829
04/11/489
GND
VOUT
1.5V
60A
• Remote output voltage sensing and inductor DCR
temperature compensation for accurate regulation
• Active voltage positioning (AVP) and nonlinear control
ensure impressive load transient performance
1.5V/60A, 3-Phase Power Supply
Figure 1 shows a 7V to 14V input, 1.5V/60A output
application. The LTC3829’s three channels run 120°
out-of-phase, which reduces input RMS current ripple
and output voltage ripple compared to single-channel
solutions. Each phase uses one top MOSFET and two
bottom MOSFETs to provide up to 20A of output current.
The LTC3829 includes unique features that maximize efficiency, including strong gate drivers, short dead times and
a programmable Stage Shedding mode, where two of the
three phases shut down at light load. Onset of Stage Shedding mode can be programmed from no load to 30% load.
Figure 2 shows the efficiency of this regulator at over 86.5%
with a 12V input and a 1.5V/60A output with Stage Shedding
mode, dramatically increasing light load efficiency.
The current mode control architecture of the LTC3829
ensures that DC load current is evenly distributed among
the three channels, as shown in Figure 3. Dynamic, cycleby-cycle current sharing performance is similarly tight
in the face of load transients.
90
1 PHASE
3 PHASE
A fast and controlled transient response is another
important requirement for modern power supplies. The
LTC3829 includes two features that reduce the peakto-peak output voltage excursion during a load step:
programmable nonlinear control or programmable active
voltage positioning (AVP). Figure 4 shows the transient
response without these features enabled. Figure 5 shows
that nonlinear control improves peak-to-peak response
by 17%. Figure 6 shows that AVP can achieve a 50%
reduction in the amplitude of voltage spikes.
Conclusion
The LTC3829’s tiny 5mm × 7mm 38-pin QFN package
belies its expansive feature set. It produces high efficiency
with a combination of strong integrated drivers and Stage
Shedding/Burst Mode® operation. It supports temperature compensated DCR sensing for high reliability. AVP
and nonlinear control improve transient response with
minimum output capacitance. Voltage tracking, multichip
operation and external sync capability fill out its menu of
features. The LTC3829 is ideal for high current applications such as telecom and datacom systems, industrial
and computer systems.
IO
20A/DIV
85
EFFICIENCY (%)
200mV
VO
100mV/DIV
60A
100μs/DIV
VIN = 12V
VO = 1.5V
fSW = 400kHz
L = 330nH
RSENSE = 1mΩ
QT = RJK0305DPB
QB = 2w RJK0330DPB
80
DN489 F04
Figure 4. Transient Performance without AVP
and Nonlinear Control
166mV
VO
100mV/DIV
STAGE SHEDDING
CCM
75
1
10
LOAD CURRENT (A)
100
DN489 F02
Figure 2. Efficiency Comparison of Stage Shedding vs CCM
VOLTAGE ACROSS SENSE RESISTOR (mV)
22
18
60A
100μs/DIV
VIN = 12V
VO = 1.5V
20
IO
20A/DIV
DN489 F05
Figure 5. Transient Performance with Nonlinear Control
16
14
12
VO
100mV/DIV
10
8
125mV
6
4
FIRST PHASE
SECOND PHASE
THIRD PHASE
2
0
–2
0
10
20
30
40
LOAD CURRENT (A)
50
60
DN489 F03
IO
20A/DIV
60A
100μs/DIV
DN489 F06
Figure 6. Transient Performance with AVP
Figure 3. Current Sharing Performance Between Phases
Data Sheet Download
www.linear.com
For applications help,
call (408) 432-1900, Ext. 3967
Linear Technology Corporation
dn489f LT/AP 0411 226K • PRINTED IN THE USA
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2011
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
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