DN280 - Tiny and Efficient Boost Converter Generates 5V at 3A from 3.3V Bus

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Tiny and Efficient Boost Converter Generates 5V at 3A
from 3.3V Bus – Design Note 280
Dongyan Zhou
applications, Burst Mode® operation can be disabled
when the SYNC/MODE pin is pulled low or driven by
an external clock. The LTC1700 can be synchronized
to an external clock ranging from 400kHz to 750kHz.
Introduction
Circuits that require 5V remain popular despite the fact
that modern systems commonly supply a 3.3V power
bus, not 5V. The tiny LTC®1700 is optimized to deliver 5V
from the 3.3V bus at very high efficiency, though it can
also efficiently boost other voltages. The small MSOP
package and 530kHz operation promote small surface
mount circuits requiring minimal board space, perfect
for the latest portable devices. By taking advantage of
the synchronous rectifier driver, the LTC1700 provides
up to 95% efficiency. To keep light load efficiency high
in portable applications, the LTC1700 draws only 180μA
in sleep mode. The LTC1700 features a start-up voltage
as low as 0.9V, adding to its versatility.
3.3V Input, 5V/3A Output Boost Regulator
Figure 1 shows a 3.3V input to 5V output boost regulator which can supply up to 3A load current. Figure 2
shows that the efficiency is greater than 90% for a load
current range of 200mA to 3A and stays above 80% all
the way down to a 3mA load.
C2 is a tantalum capacitor providing bulk capacitance
to compensate for possible long wire connections to
the input supply. In applications where the regulator’s
input is connected very close to a low impedance supply, this capacitor is not needed.
The LTC1700 uses a constant frequency, current mode
PWM control scheme. Its No RSENSE ™ feature means
the current is sensed at the main MOSFET, eliminating
the need for a sense resistor. This saves cost, space and
improves efficiency at heavy loads. For noise-sensitive
L1
3.2μH
470pF 22k
2
SGND
SW
ITH
BG
270pF
R1
316k
0.1%
C3
22μF
M1
LTC1700
470pF 4
R2 100k 1%
3
5
RUN/SS
VFB
PGND
TG
SYNC/MODE VOUT
9
6
C2
68μF
6.3V
+
C4
470μF
VIN
3.3V
±10%
100
VIN = 3.3V
VOUT = 5V
VOUT
5V/3A
90
80
70
60
7
50
DN280 F01
C1, C3: TAIYO YUDEN CERAMIC JMK325BJ226M
C2: AVX TAJB686K006R
C4: SANYO POSCAP 6TPB470M
L1: SUMIDA CEP1233R2
M1: INTERNATIONAL RECTIFIER IR7811W
M2: SILICONIX Si9803
Figure 1. 3.3V to 5V, 3A Boost Regulator
03/02/280_conv
+
M2
10
8
C1
22μF
EFFICIENCY (%)
1
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered
trademarks and No RSENSE is a trademark of Linear Technology Corporation. All
other trademarks are the property of their respective owners.
40
1
10
100
1000
LOAD CURRENT (mA)
10000
DN280 F02
Figure 2. Efficiency of the
Figure 1 Circuit
the increased gate capacitance. MOSFETs with lower
than 2.5V gate threshold voltages are recommended.
The LTC1700 is also an ideal device for single cell Li-Ion
battery to 5V applications.
2-Cell Input, 3.3V/1A Output Regulator
In digital cameras and other battery-powered devices,
the LTC1700 makes for a high efficiency boost regulator
in a small package. Figure 3 shows a 2-alkaline cell to
3.3V output circuit. This circuit can supply 1A maximum
output current. Figure 4 shows the efficiency at different
battery voltages. Efficiency of this circuit peaks at 93%.
If a lower RDS(ON) MOSFET (such as Si6466) is used
for M1, the maximum output current can be increased
to 1.4A with about a 2% reduction in efficiency due to
L1
3.3μH
470pF 33k
2
SGND
ITH
100pF
BG
8
30.1k 1%
4
3
100pF 5
RUN/SS
PGND
VFB
TG
SYNC/MODE VOUT
+
C2
68μF
6.3V
VIN
2V TO 3V
100
M2
10
C3
22μF
M1
LTC1700
470pF
52.3k
1%
SW
C1
10μF
+
C4
330μF
6.3V
VOUT
3.3V/1A
9
6
VOUT = 3.3V
VIN = 3V
90
EFFICIENCY (%)
1
Conclusion
The LTC1700 boost controller brings high efficiency
and small size to low voltage applications. Its features
are ideally suited to both battery-powered and linepowered applications.
80
VIN = 2.5V
VIN = 2V
70
60
7
50
DN280 F03
C1: TAIYO YUDEN CERAMIC JMK316BJ106ML
C2: AVX TAJB686K006R
C3: TAIYO YUDEN CERAMIC JMK325BJ226M
C4: SANYO POSCAP 6TPB330M
L1: MURATA LQN6C
M1: SILICONIX Si9804
M2: SILICONIX Si9803
40
1
10
100
LOAD CURRENT (mA)
1000
DN280 F04
Figure 4. Efficiency of the
Figure 3 Circuit
Figure 3. 2-Cell to 3.3V, 1A Boost Regulator
Data Sheet Download
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Linear Technology Corporation
For applications help,
call (408) 432-1900
dn280f_conv LT/TP 0302 341.5K • PRINTED IN THE USA
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●
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