LT1576 Linear Technology, LT1576 Datasheet - Page 28

• Manufacturer Part Number: LT1576
• Description: 1.5A/ 200kHz Step-Down Switching Regulator
• Manufacturer: Linear Technology

LT1576/LT1576-5
Dual Output SEPIC Converter
The circuit in Figure 17 generates both positive and
negative 5V outputs with a single piece of magnetics. L1
is a 33 H surface mount inductor from Coiltronics. It is
manufactured with two identical windings that can be
connected in series or parallel. 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
RELATED PARTS
28
PART NUMBER
LT1074/LT1076
LTC
LTC1149
LTC1174
LT1370
LT1371
LT1372/LT1377
LT1374
LT1376
LT1435/LT1436
LT1676/LT1776
LT1777
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
High Efficiency DC/DC Converter
High Efficiency DC/DC Converter
500kHz and 1MHz High Efficiency 1.5A Switching Regulators
4.5A, 500kHz Step-Down Switching Regulator
1.5A, 500kHz Step-Down Switching Regulator
High Efficiency Step-Down Converter
High Efficiency Step-Down Switching Regulators
Low Noise Step-Down Switching Regulator
** AVX TSPD107M010
6V TO 25V
* L1 IS A SINGLE CORE WITH TWO WINDINGS
†
COILTRONICS CTX33-2
IF LOAD CAN GO TO ZERO, AN OPTIONAL
PRELOAD OF 1k TO 5k MAY BE USED TO
IMPROVE LOAD REGULATION
INPUT
GND
+
C3
22 F
35V TANT
U
V
SHDN
IN
GND
LT1576
Figure 17. Dual Output SEPIC Converter
BOOST
V
C
BIAS
V
100 F
C
100pF
SW
C4**
FB
C
0.33 F
+
C2
L1B*
D1
1N5818
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.
33 H
L1A*
1N5818
D3
COMMENTS
40V Input, 100kHz, 5A and 2A
External FET Switches
External FET Switches
0.5A, 150kHz Burst Mode
42V, 6A, 500kHz Switch
35V, 3A, 500kHz Switch
Boost Topology
External Switches, Low Noise
7.4V to 60V Input, 100kHz/200kHz
48V Input, Internally Limited dv/dt
1N914
R2
4.99k
D2
15.8k
R1
+
+
C1**
100 F
10V TANT
C5**
100 F
10V TANT
OUTPUT
5V
OUTPUT
–5V
TM
sn1576 1576fs LT/TP 0999 4K • PRINTED IN USA
1576 F17
Operation
†
LINEAR TECHNOLOGY CORPORATION 1999