DN371 - High Efficiency 2-Phase Boost Converter Minimizes Input and Output Current Ripple

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High Efficiency 2-Phase Boost Converter Minimizes Input and
Output Current Ripple – Design Note 371
Goran Perica
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.
INPUT
10V TO 23V
22μF
w2
75k
13.3k
1
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
9
RUN
4.7μF
Switching currents 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.
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.
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respective owners.
L1
4.7μH MBRB2545
HAT2165
w2
22μF
w6
0.002Ω
OUTPUT
24V
10A
+
220μF
VOUT
100mV/DIV
1μs/DIV
DN371 F01
229k
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
SINGLEPHASE 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_conv
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.
a 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.
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
0
2
4
6
8
OUTPUT CURRENT (A)
10
12
DN371 F03
Figure 3. 12V Input to 24V Output Dual-Phase Boost
Converter Efficiency
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
INPUT
10V TO 23V
94
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
2.2μF
220μF
22μF
+
274k
0.004Ω
22μF
w2
OUTPUT
24V
10A
VOUT
100mV/DIV
1μs/DIV
10Ω
10nF
Figure 2b. Dual-Phase Boost
Converter Output Voltage Ripple
HAT2165
220k
FB
L2
DN371 F02b
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
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call (408) 432-1900
dn371f_conv LT/TP 0905 305K • PRINTED IN THE USA
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