LT1374-5 데이터 시트보기 (PDF) - Linear Technology
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LT1374-5 Datasheet PDF : 28 Pages
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LT1374
TYPICAL APPLICATION
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
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.
INPUT
6V TO 25V
C2
BOOST
0.27µF
VIN
VSW
LT1374-5 BIAS
SHDN
GND
SENSE
VC
+ C3
22µF
35V TANT
GND
* L1 IS A SINGLE CORE WITH TWO WINDINGS
BH ELECTRONICS #501-0726
** TOKIN IE475ZY5U-C304
† IF LOAD CAN GO TO ZERO, AN OPTIONAL
PRELOAD OF 1k TO 5k MAY BE USED TO
IMPROVE LOAD REGULATION
RC
470Ω
CC
0.01µF
C4** +
4.7nF
D2
1N914
L1A*
6.8µH
OUTPUT
5V
+ C1**
100µF
10V TANT
D1
MBRD340
+
L1B* D3
MBRD340
C5**
100µF
10V TANT
OUTPUT
–5V†
1374 F17
Figure 17. Dual Output SEPIC Converter
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Burst Mode is a trademark of Linear Technology Corporation.
COMMENTS
40V Input, 100kHz, 5A and 2A
External FET Switches
External FET Switches
0.5A, 150kHz Burst ModeTM Operation
PDIP LT1076
42V, 6A, 500kHz Switch
35V, 3A, 500kHz Switch
Boost Topology
External Switches, Very High Efficiency
28 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX:(408)434-0507 q www.linear-tech.com
1374fa LT/TP 0799 2K REV A • PRINTED IN USA
© LINEAR TECHNOLOGY CORPORATION 1998
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