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P RE LI MIN A R Y D ATA S HEET
T HE
I NFI N ITE
P O W ER
OF
I N NOVATIO N
Not Recommended For new Design
L IN F IN IT Y M IC ROEL E C TRON IC S I NC .
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570
1
Copyright
1997
Rev. 0.9.3b,2005-03-09
LX1570 / LX1571
PHASE MODULATED AC SYNCHRONOUS-SIDE CONTROLLER
DESCRI PTI O N
The LX1570/71 series of controller ICs are
designed to provide all control functions in a
secondary-side regulator for isolated auxiliary or
secondary
power
supplies.
Auxiliary
or
secondary-side controllers are used in a variety
of applications including multiple output off-line
power supplies, commonly found in desktop
computers,
as
well
as
telecommunications
applications. Although they can be used in all
secondary
output
applications
requiring
precision regulation, they are mainly optimized
for outputs delivering more than 3A current
where standard three-terminal regulators lack the
desired efficiency. For these applications, the
Mag Amp regulators have traditionally been
used.
However,
Mag
Amps
have
several
disadvantages. First, because they have to
withstand the maximum input voltage during a
short-circuit condition, they are "over designed",
typically by 2 times, increasing the cost and size
of the power supply. Second, Mag Amps are
inherently leading edge modulators, so they can
only approach a certain maximum duty cycle,
limited by the minimum delay and the magnetic
BH loop characteristic of the Mag Amp core.
This forces an increase in the size of the main
transformer as well as the output inductor,
resulting in higher overall system cost. The
LX1570/71 eliminates all the disadvantages of
the Mag Amp approach as well as improving
system performance and reducing overall
system cost. The LX1570/71 is a current mode
controller IC that controls the duty cycle of a
switch in series with the secondary AC output of
the power transformer in buck-derived
applications, such as forward or bridge
topologies. It offers features such as 100% duty
cycle operation for maximum energy transfer,
pulse-by-pulse and hiccup current limiting with
long off-time between the cycles for reduced
power dissipation, high-frequency operation for
smaller magnetics, soft start, and current mode
control for excellent dynamic response.
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
PRODUCT H I GHLIGHT
LX1571
V
CC
OUT
DRV
C.S.
V
FB
COMP
S.S.
GND
C
T
Aux Output
12V/8A
KEY FEATUR ES
REPLACES COSTLY MAG-AMP
CORES WITH A LOW ON-
RESISTANCE MOSFET
LOOK-AHEAD SWITCHINGTM
ENSURES SWITCH TURN ON
BEFORE THE AC INPUT TO
ACHIEVE 100% ENERGY
TRANSFER
LOWER OVERALL SYSTEM
COST
LOWER PEAK CURRENT
STRESS ON THE PRIMARY
SWITCH
ALLOWS HIGHER OPERATING
FREQUENCY AND SMALLER
OUTPUT INDUCTOR
EASY SHORT-CIRCUIT
PROTECTION
CURRENT MODE APPROACH
ACHIEVES EXCELLENT
DYNAMIC RESPONSE
APPLI CATI ONS
SECONDARY-SIDE
REGULATOR IN OFF-LINE
POWER SUPPLIES
COMPUTER POWER
SUPPLIES, 3.3V OUTPUT FOR
NEW LOW-VOLTAGE
PROCESSORS AND
MEMORIES
TELECOMMUNICATION AND
MILITARY DC/DC
CONVERTERS
Available Options Per Part#
Part #
C.L.
Threshold
C.S.
Option
Application
LX1570
-0.2V
Resistive
Sensing
Output
Current
<4A
LX1571
1V
Current
Trans-
former
Sensing
Output
Current
>4A
PACKAGE ORDER INFO
M
Plastic DIP
8-Pin
DM
Plastic SOIC
8-Pin
Y
Ceramic DIP
8-Pin
TA (
°C)
RoHS Compliant / Pb-free
Transition DC: 0503
RoHS Compliant / Pb-free
Transition DC: 0440
0 to 70
LX157xCM
LX157xCDM
-
-40 to 85
LX157xIM
LX157xIDM
-
-55 to 125
-
LX157xMY
Note: Available in Tape & Reel. Append the letters “TR” to the part number (i.e. LX1570CDM-TR).