L I N D
O C
# :
1552
LX1552/3/4/5
U
LTRA
-L
OW
S
TART
-U
P
C
URRENT
, C
URRENT
-M
ODE
PWM
T
H E
I
N F I N I T E
P
O W E R
O F
I
N N O VA T I O N
P
R O D U C T I O N
D
A T A
S
H E E T
DESCRIPTION
The LX155X family of ultra-low start-up
current (250碌A 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
excellent value for cost conscious
consumer applications.
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-
tion. Additionally, the precise oscillator
discharge current gives the power
supply designer considerable flexibility
in optimizing system duty cycle
consistency.
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 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 250碌A of supply current
permitting very efficient bootstrap
designs.
K E Y F E AT U R E S
s
ULTRA-LOW START-UP CURRENT
(150碌A typ.)
s
TRIMMED OSCILLATOR DISCHARGE
CURRENT
(卤2% typ.)
s
INITIAL OSCILLATOR FREQUENCY BETTER
THAN 卤4%
s
OUTPUT PULLDOWN DURING UVLO
s
PRECISION 2.5V REFERENCE
(卤2% max.)
p
CURRENT SENSE DELAY TO OUTPUT
(150ns typ.)
p
AUTOMATIC FEED FORWARD
COMPENSATION
p
PULSE-BY-PULSE CURRENT LIMITING
p
ENHANCED LOAD RESPONSE
CHARACTERISTICS
p
UNDER-VOLTAGE LOCKOUT WITH
HYSTERESIS
p
DOUBLE PULSE SUPPRESSION
p
HIGH CURRENT TOTEM POLE OUTPUT
(卤1Amp peak)
p
500kHz OPERATION
A P P L I C AT I O N S
PRODUCT HIGHLIGHT
s
ECONOMY OFF-LINE FLYBACK OR
FORWARD CONVERTERS
s
DC-DC BUCK OR BOOST CONVERTERS
s
LOW COST DC MOTOR CONTROL
T
YPICAL
A
PPLICATION OF
LX155X U
SING
I
TS
M
ICRO
P
OWER
S
TART
-U
P
F
EATURE
T
ABLE
1
R
ST
Design Using
SG384x UC384xA LX155x
250碌A
A
VA I L A B L E
O
P T I O N S
Part #
LX1552
LX1553
LX1554
LX1555
PER
P
A RT
#
AC
INPUT
I
ST
V
CC
Max. Start-up Current
1000碌A 500碌A
Specification (I
ST
)
Typical Start-Up
Resistor Value (R
ST
)
62K鈩?/div>
鈩?/div>
Start-Up Hysteresis Max. Duty
Voltage
Cycle
16V
8.4V
16V
8.4V
6V
0.8V
6V
0.8V
<100%
<100%
<50%
<50%
124K鈩?/div>
248K鈩?/div>
鈩?/div>
鈩?/div>
LX1552
or
Max. Start-Up Resistor
2.26W 1.13W
0.56W
Power Dissipation (P
R
)
Note: Calculation is done for universal AC input speci-
fication of V
ACMIN
= 90V
RMS
to V
ACMAX
= 265V
RMS
using the
following equation:
(Resistor curr ent is selected to be
2 * I
ST
at V
ACMIN
.)
LX1554
R
ST
=
V
AC MIN
鈭?
* I
ST
, P
R
=
2V
AC2 MAX
R
ST
PA C K A G E O R D E R I N F O R M AT I O N
T
A
(掳C)
0 to 70
-40 to 85
-55 to 125
M
Plastic DIP
8-pin
LX155xCM
LX155xIM
鈥?/div>
DM
Plastic SOIC
8-pin
LX155xCDM
LX155xIDM
鈥?/div>
D
Plastic SOIC
14-pin
LX155xCD
LX155xID
鈥?/div>
Y
Ceramic DIP
8-pin
鈥?/div>
鈥?/div>
LX155xMY
PW
TSSOP
20-pin
LX155xCPW
鈥?/div>
鈥?/div>
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 漏 1994
Rev. 1.0a 1/01
11861 W
ESTERN
A
VENUE
, G
ARDEN
G
ROVE
, CA. 92841
1
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