DN532 - High Efficiency 100mA Synchronous Buck Converter with Wide Input Range from 4V to 150V

High Efficiency 100mA Synchronous Buck Converter with
Wide Input Range from 4V to 150V
Design Note 532
Charlie Zhao
4V to 150V Input to 3.3V Output,
100mA Buck Converter
Figure 1 shows a 3.3V output, 100mA maximum
load current synchronous buck converter, with wide
input range from 4V to 150V. The LTC3639 has three
programmable fixed output voltages 1.8V, 3.3V and
5V. These fixed outputs use an internal feedback
resistor divider and can be simply selected with the
VPRG1 and VPRG2 pins. For 3.3V output, just connect
VPRG1 to ground and tie VPRG2 to the SS pin. The VFB
pin is directly connected to the output without using
an external resistor divider. Efficiency curves with
different input voltages are shown in Figure 2.
Introduction
The wide 4V to 150V input range of the LTC ®3639 stepdown DC/DC converter allows automotive, avionics
and distributed power systems to:
• Cover extensive transient requirements
• Enable multiple wide-ranging input power sources,
such as a high voltage DC bus with a low voltage
battery backup
• Create a universal power supply to cover a variety
of input sources, thereby reducing inventory and
the cost of design and manufacture
The LTC3639 converts at high efficiency with internal high side and low side power MOSFETs. It can
support up to 100mA output current and features a
programmable peak current limit. Its output voltage
range is also broad, from 0.8V to the input voltage.
The integrated high side MOSFET can work at 100%
duty cycle for low dropout operation. High efficiency
is achieved across the wide input and output voltage
ranges. Burst Mode ® operation and low quiescent
current are also features of this synchronous buck
converter. The loop is inherently stable without
compensation because of the hysteretic nature of the
control architecture, resulting in a simple easy to use
application circuit.
VIN
4V TO 150V
1µF
200V
36V to 72V Input to 24V Output,
100mA Buck Converter
The LTC3639 has a very wide output voltage range,
from 0.8V to the input voltage. Besides the selectable three fixed output voltages, an adjustable output
voltage can be set with an external resistor divider.
Figure 3 shows an application example of a 24V output,
100mA synchronous step-down converter. The input
voltage range is controlled from 36V to 72V, with the
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are
registered trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
TDK SLF12555T-102MR34
1000µH
SW
VIN
LTC3639
RUN
VFB
OVLO
VPRG1
VOUT
3.3V
10µF 100mA
SS
VPRG2
GND
dn532 F01
Figure 1. 4V to 150V Input to 3.3V Output, 100mA Synchronous Buck Converter
11/14/532
part’s wide voltage range makes even large negative output voltages realizable. Figure 4 shows the
implementation of a –15V output regulator from a 4V
to 135V input. Since the output is connected to the
ground pin, the maximum input voltage is limited to
the sum of 150V and the –15V regulated output, or
135V. The maximum output current for the LTC3639
in this positive-to-negative configuration is about
100mA • VIN/(VIN+|VOUT|).
Effciency vs Load Current, VOUT = 3.3V
100
90
ISET OPEN
EFFICIENCY (%)
80
70
60
50
40
30
VIN = 12V
VIN = 36V
VIN = 72V
VIN = 150V
20
10
0
0.1
VIN
4V TO 135V
100
10
1
LOAD CURRENT (mA)
dn532 F02
Figure 2. Efficiency Curves of the Converter in Figure 1
220µH
VIN
36V TO 72V
SW
VIN
LTC3639
2.2M
187k
VOUT
24V
100mA
FBO
62k
ISET
1µF
OVLO
30.9k
10µF
SS
VPRG1
VPRG2
GND
49.9k
dn532 F03
Figure 3. 36V to 72V Input to 24V, 100mA Buck Converter
with Input Overvoltage and Undervoltage Lockout
overvoltage lockout and undervoltage lockout features
of the LTC3639. The input operating range is easily
set with a resistor divider from the VIN to the RUN pin
and the OVLO pin, as shown in Figure 3.
Negative Output Voltage Applications
An additional useful application for the LTC3639 is to
generate a negative voltage from a positive one. The
Data Sheet Download
www.linear.com/LTC3639
Linear Technology Corporation
CIN
1µF
200V
VIN
SW
LTC3639
RUN
VFB
SS
FBO
VPRG1
ISET
VPRG2 OVLO
GND
200k
102k
dn532 F04
COUT
10µF
25V
VOUT
–15V
Figure 4. 4V to 135V Input to –15V Output
Positive-to-Negative Regulator
VFB
RUN
L1
220µH
Conclusion
The LTC3639 has a very wide input voltage range,
very wide output voltage range, integrated power
MOSFETs, low quiescent current (1.4µA in shutdown
and 12µA in sleep mode) and high efficiency across
a wide load current range. Rich features include programmable or adjustable output, adjustable current
limit, no compensation required, internal or external
soft-start, programmable overvoltage and undervoltage lockout. Additionally, the thermally enhanced small
MSE package and simple application circuit offer a
high performance, small and cost effective DC/DC
converter solution for automotive systems, avionics, distributed power systems, medical devices and
industrial control supplies.
For applications help,
call (408) 432-1900, Ext. 3258
dn532f LT/AP 1114 111K • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2014
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