DN453 - 4-Phase Boost Converter Delivers 384W with no Heat Sink

4-Phase Boost Converter Delivers 384W with no Heat Sink
Design Note 453
Victor Khasiev
Introduction
High power boost converters are becoming increasingly
popular among designers in the automotive, industrial
and telecom industries. When power levels of 300W or
more are required, high efficiency (low power loss) is
imperative in the power train components to avoid the
need for bulky heat sinks and forced-air cooling. Interleaving power stages (multiphase operation) improves
efficiency and reduces ripple voltage and currents in
both the input and output capacitors, allowing the use
of smaller filter components.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
L1 19.4μH
D1 PDS760
VIN 5V TO 18V
L2 19.4μH
3×10μF
84.5k
D2 PDS760
HAT2266H
24.9k
1nF
U1
1
2
3
VOUT
4
66.5k
475k
5
0.1μF
6
68k
7
12.4k
8
10nF
9
220pF
Q1
10
11
12
DMAX
3V8
SLOPE
RUN
LTC3862
BLANK
VIN
INTVCC
PH/MODE
NC
FREQ
SS
PGND
ITH
G1
SENSE1+
FB
10
24
10nF
6m
21
20
19
15
VOUT
48V
8A
1μF
4.7μF
17
4×120μF
18
23
+
14×6.8μF
HAT2266H
Q2
– 22
SENSE1
SGND
G2
CLKOUT
16
10
+ 13
SYNC
SENSE2
PLLFLTR
SENSE2–
10nF
6m
14
D3 PDS760
L3 19.4μH
VIN
L4 19.4μH
3×10μF
D4 PDS760
HAT2166H
Q3
1nF
U2
1
2
3
4
66.5k
5
6
220pF
7
8
9
10
11
12
10nF
10k
DMAX
3V8
SLOPE
RUN
LTC3862
BLANK
PH/MODE
FREQ
SS
ITH
VIN
INTVCC
NC
PGND
G1
6m
20
19
15
1μF
4.7μF
17
18
23
SENSE1+
SGND
22
SENSE1–
G2
10nF
21
FB
CLKOUT
10
24
HAT2166H
Q4
16
SYNC
SENSE2+
13
PLLFLTR
SENSE2–
14
L1 TO L4: PAPA2050-193
10
10nF
6m
DN453 F01
Figure 1. A 4-Phase Boost Converter Based on the LTC3862 Produces 48V at 8A from a 5V to 18V Input
10/08/453
The power train includes four inductors L1-L4, four
MOSFETs Q1-Q4, four diodes D1-D4, along with the input
and output filter capacitors. The ITH, FB, SS and RUN
pins of the two controllers are connected together, which
forces current share balancing and consistent start up
timing between the phases, and forces both controllers
to turn on at the same input voltage.
This converter can deliver 8A at 48V continuously from a
12V to 18V input. It can even support the 48V output with
input voltages down to 5V, at a reduced output current.
Figure 3 shows the converter efficiency above 96% for
much of the load range. The transient response to a 3A
load step as shown in Figure 4 has only a 100mV deviation from nominal.
Up to 12 power stages can be paralleled and clocked
out-of-phase for even higher power applications. The
LTC3862 has an input voltage range of 4V to 36V and
an output voltage that is dependent upon the choice of
external components, making it an excellent choice for
12V automotive high power boost converter applications
such as audio amplifiers and fuel injection systems.
Conclusion
The LTC3862 2-phase controller is a powerful building
block for multiphase boost converter applications that
demand high efficiency, low power loss, reduced ripple
voltage and currents, and have a small solution size without
the need for forced-air cooling or heat sinks.
97.8
12VIN
14VIN
18VIN
97.6
97.4
EFFICIENCY (%)
384W Boost Converter
Figure 1 shows a 4-phase boost converter using two
2-phase LTC®3862 current mode controllers configured in
a master-slave configuration (as described in the LTC3862
data sheet). U1 is the master controller; it generates the
clock signal that serves to synchronize the two controllers.
Synchronization is achieved by connecting U1’s CLKOUT
pin to U2’s SYNC pin and terminating the PLLFLTR pin of
U2 with a lowpass filter. Each controller operates with a
180° phase shift between its two channels, and there is a
90° phase shift between the two controllers as defined by
the state of U1’s PHASEMODE pin, to form an interleaved
4-phase system as shown in Figure 2.
97.2
97.0
96.8
96.6
96.4
96.2
96.0
2
3
4
5
IO (A)
6
8
7
DN453 F03
Figure 3. Efficiency vs Output Current Input Voltage
for Multiple VIN.
50V/DIV
Q1
50V/DIV
Q2
50V/DIV
Q3
50V/DIV
Q4
1μs/DIV
VOUT
100mV/DIV
IOUT
2A/DIV
DN453 F02
Figure 2. Timing Diagram Showing 4-Phase Operation
2ms/DIV
DN453 F04
Figure 4. Transient Response for a Current Load Step
from 2A to 5A.
Data Sheet Download
For applications help,
call (408) 432-1900, Ext. 2593
www.linear.com
Linear Technology Corporation
dn453f LT/TP 1008 246K • PRINTED IN THE USA
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2008
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
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