LX1552/3/4/5
URRENT, C URRENT- MODE PWM
U
LTRA- LOW
S
TART- U
P
C
P
R O D U C T I O N D A T A S H E E T
T
H E
I
N F I N I T E
P
O W E R O F
I N N O V A T I O N
KEY FEATURES
DESCRIPTION
The LX155x family of ultra-low start-up current
(250µA max), current mode control ICs offer new
levels of energy efficiency for offline converter
Additionally, the precise oscillator discharge
current gives the power supply designer
considerable flexibility in optimizing system duty
cycle consistency.
Ultra-Low Start-up Current (150µA
Typical)
Trimmed Oscillator Discharge
Current (±2% Typical)
Initial Oscillator Frequency Better
Than ±4%
Output Pulldown During UVLO
Precision 2.5V Reference (±2
maximum)
Current Sense Delay to Output
(150ns Typical)
Automatic Feed Forward
Compensation
Pulse-by-Pulse Current Limiting
Enhanced Load response
Characteristics
Under-Voltage Lockout with
Hysteresis
Double Pulse Suppression
applications.
They are ideally optimized for
personal computer and CRT power supplies
although they can be used in any number of off-line
applications where energy efficiency is critical.
Coupled with the fact that the LX155x series
requires a minimal set of external components, the
series offers an excellent value for cost conscious
consumer applications.
The current mode architecture demonstrates
improved load regulation, pulse by pulse current
limiting and inherent protection of the power
supply output switch. The LX155x includes a
bandgap reference trimmed to 1%, an error
amplifier, a current sense comparator internally
clamped to 1V, a high current totem pole output
stage for fast switching of power MOSFETs, and
an externally programmable oscillator to set
operating frequency and maximum duty cycle.
The under voltage lock-out circuitry is designed to
operate with as little as 250µA of supply current
permitting very efficient bootstrap designs.
Optimizing energy efficiency, the LX155x series
demonstrates
a significant power reduction as
compared with other similar off-line controllers.
Table 1 compares the SG384x, UC384xA and the
LX155x start-up resistor power dissipation. The
LX155x offers an overall 4X reduction in power
dissipation.
High Current Totem Pole Output
(±1A Peak)
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
500KHz Operation
PRODUCT HIGHLIGHT
APPLICATIONS
Typical Application of LX155x Using Its MicroPower Start-Up Feature
Economy Off-Line Flyback or
Forward Converters
DC-DC Buck or Boost Converters
Low Cost DC Motor Control
Design Using
Max. Start-up Current
SG384x UC384xA LX155x
R
ST
1000µA
62KΩ
500µA
124KΩ
1.13W
250µA
248KΩ
0.56W
Specification (IST
Typical Start-up Resistor
Value (RST
)
)
I
ST
AC
Max. Start-up Resistor
Power Dissipation (PR)
INPUT
2.26W
V
CC
Available Options Per part#
Part #
Start-Up
Voltage
16V
8.4V
16V
Max. Duty
Hysteresis
Note: Calculation is done for universal AC input
specification of VACMIN = 90VRMS to VACMAX = 256VRMS using
the following equation: (resistor current is selected to be 2
LX1552
or
Cycle
<100%
<100%
<50%
LX1552
LX1553
LX1554
LX1555
6V
0.8V
6V
LX1554
* IST @ VACMIN
)
2VAC
8.4V
0.8V
<50%
VACMIN
2 • IST
2
MAX
RST
=
,P =
R
RST
PACKAGE ORDER INFO
Ceramic DIP
8-Pin
Plastic TSSOP
20-Pin
RoHS Compliant / Pb-free
Transition DC: 0442
Plastic DIP
8-Pin
RoHS Compliant / Pb-free
Transition DC: 0503
Plastic SOIC
8-Pin
Plastic SOIC
14-Pin
M
DM
D
Y
PW
TA (°C)
RoHS Compliant / Pb-free
Transition DC: 0440
RoHS Compliant / Pb-free
Transition DC: 0440
0 to 70
-40 to 85
-55 to 125
LX155xCM
LX155xIM
-
LX155xCDM
LX155xIDM
-
LX155xCD
LX155xID
-
-
-
LX155xCPW
-
-
LX155xMY
Note: Available in Tape & Reel. Append the letters “TR” to the part number (i.e. LX1552CDM-TR).
L
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F
I N I T Y
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I C R O E L E C T R O N I C S
I
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Copyright © 1994
Rev. 1.0b,2005-03-01
1
11861 WESTERN
A
VENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570