LT1374C Linear Technology, LT1374C Datasheet - Page 28

• Manufacturer Part Number: LT1374C
• Description: 4.5A/ 500kHz Step-Down Switching Regulator
• Manufacturer: Linear Technology

LT1374
RELATED PARTS
Dual Output SEPIC Converter
The circuit in Figure 17 generates both positive and
negative 5V outputs with a single piece of magnetics. The
two inductors shown are actually just two windings on a
standard BH Electronics inductor. The topology for the 5V
output is a standard buck converter. The – 5V topology
would be a simple flyback winding coupled to the buck
converter if C4 were not present. C4 creates the SEPIC
(Single-Ended Primary Inductance Converter) topology
which improves regulation and reduces ripple current in
L1. Without C4, the voltage swing on L1B compared to
L1A would vary due to relative loading and coupling
28
PART NUMBER
LT1074/LT1076
LTC
LTC1149
LTC1174
LT1176
LT1370
LT1371
LT1372/LT1377
LTC1735
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL
®
1148
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] FAX: [phone] www.linear-tech.com
APPLICATION
DESCRIPTION
Step-Down Switching Regulators
High Efficiency Synchronous Step-Down Switching Regulator
High Efficiency Synchronous Step-Down Switching Regulator
High Efficiency Step-Down and Inverting DC/DC Converter
Step-Down Switching Regulator
High Efficiency DC/DC Converter
High Efficiency DC/DC Converter
500kHz and 1MHz High Efficiency 1.5A Switching Regulators
High Efficiency Step-Down Converter
** TOKIN IE475ZY5U-C304
6V TO 25V
* L1 IS A SINGLE CORE WITH TWO WINDINGS
†
BH ELECTRONICS #501-0726
IF LOAD CAN GO TO ZERO, AN OPTIONAL
PRELOAD OF 1k TO 5k MAY BE USED TO
IMPROVE LOAD REGULATION
INPUT
GND
U
+
C3
22 F
35V TANT
Figure 17. Dual Output SEPIC Converter
V
SHDN
IN
GND
LT1374-5
BOOST
V
C
SENSE
R
470
BIAS
V
C
C
0.01 F
4.7nF
SW
C4**
C
losses. C4 provides a low impedance path to maintain an
equal voltage swing in L1B, improving regulation. In a
flyback converter, during switch on time, all the converter’s
energy is stored in L1A only, since no current flows in L1B.
At switch off, energy is transferred by magnetic coupling
into L1B, powering the – 5V rail. C4 pulls L1B positive
during switch on time, causing current to flow, and energy
to build in L1B and C4. At switch off, the energy stored in
both L1B and C4 supply the – 5V rail. This reduces the
current in L1A and changes L1B current waveform from
square to triangular. For details on this circuit see Design
Note 100.
0.27 F
+
C2
COMMENTS
40V Input, 100kHz, 5A and 2A
External FET Switches
External FET Switches
0.5A, 150kHz Burst Mode
PDIP LT1076
42V, 6A, 500kHz Switch
35V, 3A, 500kHz Switch
Boost Topology
External Switches, Very High Efficiency
L1B*
D1
MBRD340
6.8 H
MBRD340
1N914
L1A*
D2
D3
+
+
C1**
100 F
10V TANT
C5**
100 F
10V TANT
TM
Operation
1374fa LT/TP 0799 2K REV A • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1998
OUTPUT
5V
OUTPUT
–5V
1374 F17
†