LIN DOC #: 1552
LX1552/3/4/5
U
LTRA-LOW
S
TART-U
P
C
URRENT, CURRENT-MODE PWM
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
P R O D U C T I O N D A T A S H E E T
DESCRIPTION
KEY FEATURES
■ ULTRA-LOW START-UP CURRENT
The LX155X family of ultra-low start-up
current (250µA max.), current mode
control IC's offer new levels of energy
efficiency for offline converter applica-
tions. 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
tion. Additionally, the precise oscillator
discharge current gives the power
supply designer considerable flexibility
in optimizing system duty cycle
consistency.
(150µA typ.)
■ TRIMMED OSCILLATOR DISCHARGE
CURRENT (±±2 typ.)
■ INITIAL OSCILLATOR FREQUENCY BETTER
THAN ±±4
The current mode architecture
■ OUTPUT PULLDOWN DURING UVLO
■ PRECISION 2.5V REFERENCE (±±2 max.)
p CURRENT SENSE DELAY TO OUTPUT
(150ns typ.)
p AUTOMATIC FEED FORWARD
COMPENSATION
p PULSE-BY-PULSE CURRENT LIMITING
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 com-
parator internally clamped to 1V, a high
current totem pole output stage for fast
switching of power mosfet's, and an
externally programmable oscillator to
set operating frequency and maximum
duty cycle. The undervoltage lock-out
circuitry is designed to operate with as
little as 250µA of supply current
permitting very efficient bootstrap
designs.
excellent value for cost conscious
consumer applications.
p ENHANCED LOAD RESPONSE
CHARACTERISTICS
p UNDER-VOLTAGE LOCKOUT WITH
HYSTERESIS
p DOUBLE PULSE SUPPRESSION
p HIGH CURRENT TOTEM POLE OUTPUT
Optimizing energy efficiency, the
LX155X series demonstrates a signifi-
cant 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 dissipa-
(±1Amp peak)
p 500kHz OPERATION
APPLICATIONS
PRODUCT HIGHLIGHT
■ ECONOMY OFF-LINE FLYBACK OR
FORWARD CONVERTERS
TYPICAL APPLICATION OF LX155X USING ITS
MICROPOWER START-UP FEATURE
■ DC-DC BUCK OR BOOST CONVERTERS
■ LOW COST DC MOTOR CONTROL
T A B L E 1
A V A I L A B L E O P T I O N S P E R P A R T #
Design Using
SG384x UC384xA LX155x
R
ST
Part #
Start-Up Hysteresis Max. Duty
Max. Start-up Current
Specification (IST)
1000µA 500µA 250µA
Voltage
16V
Cycle
<100%
<100%
<50%
<50%
I
ST
AC
Typical Start-Up
Resistor Value (RST)
INPUT
LX1552
LX1553
LX1554
LX1555
6V
0.8V
6V
62KΩ 124KΩ 248KΩ
V
CC
8.4V
16V
Max. Start-Up Resistor
Power Dissipation (PR)
2.26W 1.13W 0.56W
LX1552
or
Note: Calculation is done for universal AC input speci-
fication of VACMIN= 90VRMS to VACMAX= 265VRMS using the
following equation: (Resistor current is selected to be
LX1554
8.4V
0.8V
2
IST at VACMIN.)
*
2
VAC MIN
2VAC
MAX
RST
=
, PR =
√2
I
RST
*
ST
PACKAGE ORDER INFORMATION
Plastic DIP
8-pin
Plastic SOIC
8-pin
Plastic SOIC
14-pin
Ceramic DIP
8-pin
TSSOP
PW
20-pin
TA (°C)
M
DM
D
Y
0 to 70
-40 to 85
-55 to 125
LX155xCM
LX155xCDM
LX155xIDM
—
LX155xCD
LX155xID
—
—
—
LX155xCPW
LX155xIM
—
—
—
LX155xMY
Note: All surface-mount packages are available in Tape & Reel. Append the letter "T" to part number. (i.e. LX1552CDMT)
F O R F U R T H E R I N F O R M AT I O N C A L L ( 7 1 4 ) 8 9 8 - 8 1 2 1
Copyright © 1994
Rev. 1.0a 1/01
1
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841