DN550 - 60V, 4A Synchronous Monolithic Step-Down Regulator Has Rail-to Rail Operation

60V, 4A Synchronous Monolithic Step-Down Regulator Has
Rail-to Rail Operation
Design Note 550
Victor Khasiev
Introduction
The LTC3649 is a high efficiency synchronous monolithic step-down regulator, which integrates top and
bottom N-channel MOSFETs on the die. This regulator
features a wide input voltage range, 3.1V to 60V, and
a wide output voltage range from 0V to (VIN − 0.5V).
This extremely wide range of operating voltages
makes the LTC3649 especially attractive for industrial,
medical and transportation applications, where the
rail voltage can be less than 5V or above 40V during
voltage transient events. The input voltage range of
the LTC3649 also covers mass produced and widely
accepted 12V and 24V solar panels, where it is used as
a downstream converter in alternative energy systems.
In contrast to the majority of DC/DC controllers and
regulators, the output voltage of LTC3649 can be
programmed by either a single resistor or the reference
of its internal error amplifier. It also features a current
monitoring output, IMON. The LTC3649’s unique comR2
2.1k
4.7n
bination of features opens up interesting applications
in power adapters and portable computer systems.
Circuit Description and Functionality
A 5V output power supply is shown in Figure 1. This
circuit is centered on the extremely small footprint
high voltage step-down DC/DC LTC3649. The input
voltage extends up to 60V and the output is set to 5V
at 4A. Only a few additional components are required
for the complete solution, including inductor L1 and
a few passive components.
The feedback loop can be closed by external components off the ITH pin or by internal compensation.
The ITH pin should be connected to INTVCC through
optional resistor RITH if its internal loop compensation is used. The output voltage is set by resistor
RST. Despite the small size of the converter and
integrated switching MOSFETs, efficiency reaches
95%, as shown in Figure 2.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered
trademarks of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
RITH
OPT
10pF
2.2µF
10nF
INTVCC
ITH
RST
100k
VINREG
ISET
10k
LTC3649
IMON
GND
470pF
SGND
INTVCC
100k
357k
1M
137k
VIN
MODE/SYNC
RUN
PGOOD
GND
RT
PGDFB
GND
GND
CIN1 SUN ELECT. 63CE10KX
CIN2 MURATA GRM32ER71J106KA12L
L1 COILCRAFT XAL5050-562MEB
INTVCC
10k
VIN
VIN
SW
SW
SW
SW
SW
SW
SW
BOOST
VOUT
EXTVCC
VIN 5.5V-60V
CIN2
10µF
L1
5.6µH
C6
0.1µF
+
CIN1
10µF/63V
VOUT 5V AT 4A
COUT2
10µF
+
COUT1
150µF
16V
100Ω
10Ω
dn550 F04
Figure 1. LTC3649 Step-Down Converter Delivers 5V at 4A from Inputs Up to 60V
05/16/550
to the output current. Increases in the load current
proportionally change the voltage on the V_TERM
output, but the load voltage at the end of the cable
remains unchanged, as shown in Figure 4. A similar
approach can be used for remote sensing. See the
LTC3649 data sheet for details.
95
93
89
87
85
83
81
79
75
0.0
4.5
12VIN
24VIN
48VIN
77
0.5
1.0
1.5 2.0 2.5 3.0
LOAD CURRENT (A)
3.5
4.0
OUTPUT VOLTAGE (V)
EFFICIENCY (%)
91
dn550 F02
Figure 2. Efficiency vs Load and Input
Voltage for Circuit in Figure 1
4.0
3.5
3.0
V_TERM
V_LOAD
Figure 3 shows the LTC3649 in an application with
cable drop due to a remote load. This approach can
be used in systems which do not have additional
remote sense wires in long power cables. The circuit
takes advantage of the current monitoring terminal
IMON and the ability set the output voltage with an
external resistor.
2.5
0.0
0.5
1.0
1.5 2.0 2.5 3.0
LOAD CURRENT (A)
3.5
4.0
dn550 F04
Figure 4. Cable Drop Operation Load Curves
Conclusion
LTC3649 is a highly integrated, high performance
step-down regulator, with the input and output
ranges that enable it to satisfy the requirements of
industrial test and measurement, and transportation
applications, as well as regulating solar panels and
portable devices.
In this example, two 0.1Ω resistors simulate the
impedance of the power wires in a long cable. Resistors RC1 and RC2 set the voltage reference and are
fed by two current sources: from pin ISET, a constant
50µA, and from pin IMON, a current proportional
RITH
0Ω
2.2µF
10nF
RC2
8.06k
RC1
59k
470pF
ITH
INTVCC
ISET
VINREG
VIN
LTC3649
VIN
IMON
GND
100k
INTVCC
200k
1M
137k
VIN
RUN
PGOOD
GND
PGDFB
GND
GND
10k
VIN
CIN2
10µF
SW
SW
SW
SW
SW
SW
SW
SGND
MODE/SYNC
RT
INTVCC
BOOST
VOUT
EXTVCC
CIN1 SUN ELECT. 63CE10KX
CIN2 MURATA GRM32ER71J106KA12L
L1 COILCRAFT XAL5050-562MEB
+
CIN1
10µF/63V
CABLE
L1
5.6µH
C6
0.1µF
0.1Ω
COUT2
10µF
+
COUT1
150µF/16V
0.1Ω
100Ω
0.1Ω
dn550 F03
Figure 3. The LTC3649 Can Provide Cable Drop Compensation for Long PCB Traces
Data Sheet Download
www.linear.com/LTC3649
Linear Technology Corporation
For applications help,
call (408) 432-1900, Ext. 3161
DN550 LT/AP 0516 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 2016
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