High Efficiency 2-Phase Boost Converter Minimizes Input and
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High Efficiency 2-Phase Boost Converter Minimizes Input and
Output Current Ripple – Design Note 371
Goran Perica
also increase proportional to the output-to-input voltage
conversion ratio, so if the input voltage is low, the
switching currents can overwhelm a simple boost converter and generate unacceptable EMI.
Introduction
Many automotive and industrial applications require higher
voltages than is available on the input power supply rail.
A simple DC/DC boost converter suffices when the power
levels are in the 10W to 50W range, but if higher power
levels are required, the limitations of a straightforward
boost converter become quickly apparent. Boost converters convert a low input voltage to a higher output
voltage by processing the input current with a boost
inductor, power switch, output diode and output capacitor. As the output power level increases, the currents in
these components increase as well. Switching currents
INPUT
10V TO 23V
22µF
×2
75k
13.3k
1
9
VIN
LTC1871-7
7
ITH
GATE
10
4
SENSE
FREQ
8
5
MODE/SYNC INTVCC
6
3
VFB
GND
4.7nF 12k 2
80.6k
12.4k
RUN
4.7µF
For example, consider Figure 1, a 12V input to 24V, 10A
output switching converter operating at 300kHz. The
currents processed by the converter in Figure 1 are shown
in the first row of Table 1. The relatively high current levels
in the switcher are reflected in high input and output ripple
currents, which results in increased EMI.
, LTC, LT and Burst Mode are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners.
L1
4.7µH MBRB2545
HAT2165
×2
22µF
×6
0.002Ω
OUTPUT
24V
10A
+
220µF
VOUT
100mV/DIV
DN371 F01
229k
1µs/DIV
L1: COOPER HC3-4R7
ALL CERAMIC CAPACITORS ARE X7R, TDK
DN371 F01b
Figure 1b. Single-Phase Boost
Converter Output Voltage Ripple
Figure 1a. Single-Phase Boost Converter: Can be Used
to Convert 12V Input to 24V, 10A Output
Table 1. Dual-Phase Boost Converter Has Lower Input and Output Ripple Currents and Voltages Than Single-Phase Boost
Converter
INPUT RMS
CURRENT
INPUT RIPPLE
CURRENT
MOSFET
RMS DRAIN
CURRENT
OUTPUT
DIODE
RMS CURRENT
OUTPUT
CAPACITOR
RMS CURRENT
OUTPUT
CAPACITOR
FREQUENCY
OUTPUT
VOLTAGE
RIPPLE
SINGLE-PHASE
BOOST
CONVERTER
21.1A
4.2AP-P
15.4A
14.4A
10.5A
300kHz
212mV
DUAL-PHASE
BOOST
CONVERTER
20.7A
0.17AP-P
2 × 7.4A
2 × 7.2A
1.9A
600kHz
65mV
09/05/371
240W boost supply application, the power dissipation of
12.9W is relatively easy to manage in a well laid out, large
multilayer PCB with some forced airflow.
The circuit shown in Figure 2 performs the same DC/DC
conversion, but with greatly reduced input and output
ripple, significantly reducing EMI, and at a higher effective switching frequency, which allows the use of two
22µF output capacitors versus six 22µF output capacitors
required in Figure 1.
Conclusion
The simple LT3782 dual-phase switching boost converter
improves on single-phase alternatives by allowing high
power output with lower ripple currents, reduced heat
dissipation and a more compact design.
The trick is the 2-phase boost topology, which interleaves
two 180° out-of-phase output channels to mutually cancel out input and output ripple current—the results are
shown in the second row of Table 1. Each phase operates
at 50% duty cycle and the rectified output currents from
each phase flow directly to the load—namely the low
inductor ripple current—so only a small amount of output
current (shown in Table 1) is handled by the output
capacitors.
96
EFECIENCY (%)
95
®
The centerpiece of the design in Figure 2 is the LT 3782
2-phase current mode PWM controller. Current mode
operation ensures balanced current sharing between the
two power converters resulting in even power dissipation
between the power stages.
L1
93
92
91
90
The efficiency of the dual-phase converter, shown in
Figure 3, is high enough that it can be built entirely with
surface mount components—no need for heat sinks. In a
INPUT
10V TO 23V
94
0
2
4
6
8
OUTPUT CURRENT (A)
10
12
DN371 F03
Figure 3. 12V Input to 24V Output Dual-Phase
Boost Converter Efficiency
UPS840
825k
BGATE1
SEN1P
RUN
RSET
DELAY
62k
DCL
59k
4.7nF
4.7nF 15k
LT3782
GBIAS
SLOPE
GBIAS1
SS
GBIAS2
GND
SEN2N
VEE1
SEN2P
VEE2
BGATE2
VC
100pF
10nF
SEN1N
VCC
HAT2165
10Ω
0.004Ω
22µF
2.2µF
0.004Ω
220µF
+
274k
22µF
×2
OUTPUT
24V
10A
10Ω
10nF
1µs/DIV
L2
DN371 F02b
Figure 2b. Dual-Phase Boost
Converter Output Voltage Ripple
HAT2165
220k
FB
VOUT
100mV/DIV
UPS840
24.9k
DN371 F02
L1, L2: PULSE PB2020-153
ALL CERAMIC CAPACITORS ARE X7R TDK
Figure 2a. Dual-Phase Boost Converter Reduces EMI and Ripple
Currents with a Minimum Input and Output Filtering
Data Sheet Download
http://www.linear.com
Linear Technology Corporation
For applications help,
call (408) 432-1900, Ext. 2593
dn371f LT/TP 0905 305K • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2005
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