April 1998
LM2587
SIMPLE SWITCHER® 5A Flyback Regulator
General Description
Features
n Requires few external components
The LM2587 series of regulators are monolithic integrated
circuits specifically designed for flyback, step-up (boost), and
forward converter applications. The device is available in 4
different output voltage versions: 3.3V, 5.0V, 12V, and adjust-
able.
n Family of standard inductors and transformers
n NPN output switches 5.0A, can stand off 65V
n Wide input voltage range: 4V to 40V
n Current-mode operation for improved transient
response, line regulation, and current limit
n 100 kHz switching frequency
n Internal soft-start function reduces in-rush current during
start-up
n Output transistor protected by current limit, under
voltage lockout, and thermal shutdown
Requiring a minimum number of external components, these
regulators are cost effective, and simple to use. Included in
the datasheet are typical circuits of boost and flyback regula-
tors. Also listed are selector guides for diodes and capacitors
and a family of standard inductors and flyback transformers
designed to work with these switching regulators.
The power switch is a 5.0A NPN device that can stand-off
65V. Protecting the power switch are current and thermal
limiting circuits, and an undervoltage lockout circuit. This IC
contains a 100 kHz fixed-frequency internal oscillator that
permits the use of small magnetics. Other features include
soft start mode to reduce in-rush current during start up, cur-
rent mode control for improved rejection of input voltage and
output load transients and cycle-by-cycle current limiting. An
±
n System Output Voltage Tolerance of 4% max over line
and load conditions
Typical Applications
n Flyback regulator
n Multiple-output regulator
n Simple boost regulator
n Forward converter
±
output voltage tolerance of 4%, within specified input volt-
ages and output load conditions, is guaranteed for the power
supply system.
Flyback Regulator
DS012316-1
Ordering Information
Package Type
NSC Package
Drawing
T05D
Order Number
5-Lead TO-220 Bent, Staggered Leads
5-Lead TO-263
LM2587T-3.3, LM2587T-5.0, LM2587T-12, LM2587T-ADJ
LM2587S-3.3, LM2587S-5.0, LM2587S-12, LM2587S-ADJ
TS5B
5-Lead TO-263 Tape and Reel
TS5B
LM2587SX-3.3, LM2587SX-5.0, LM2587SX-12,
LM2587SX-ADJ
SIMPLE SWITCHER® and Switchers Made Simple® are registered trademarks of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation
DS012316
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