LX1552 Datasheet, PDF (1/18 Pages) Microsemi Corporation – ULTRA-LOW START-UP CURRENT, 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 VAT I O N
L I N DO C # : 1552
LX1552/3/4/5
ULTRA-LOW START-UP CURRENT, CURRENT-MODE PWM
PRODUCTION DATA SHEET
DESCRIPTION
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
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 250µA of supply current
permitting very efficient bootstrap
designs.
PRODUCT HIGHLIGHT
TYPICAL APPLICATION OF LX155X USING ITS
MICROPOWER S TART-UP FEATURE
TABLE 1
AC
INPUT
R _ST
I _ST
V_CC
LX1552
or
LX1554
Design Using
SG384x UC384xA LX155x
Max. Start-up Current
Specification (I_ST)
1000µA
500µA
250µA
Typical Start-Up
Resistor Value (R_ST)
62KΩ 124KΩ 248KΩ
Max. Start-Up Resistor
Power Dissipation (P_R)
2.26W
1.13W
0.56W
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
R_ST =
V_{AC MIN}
√2 _* I_ST
,
P_R =
2V
2
AC
MAX
R_ST
KEY FEATURES
s ULTRA-LOW START-UP CURRENT
(150µA typ.)
s TRIMMED OSCILLATOR DISCHARGE
CURRENT (±2% typ.)
s INITIAL OSCILLATOR FREQUENCY BETTER
THAN ±4%
s OUTPUT PULLDOWN DURING UVLO
s 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
p ENHANCED LOAD RESPONSE
CHARACTERISTICS
p UNDER-VOLTAGE LOCKOUT WITH
HYSTERESIS
p DOUBLE PULSE SUPPRESSION
p HIGH CURRENT TOTEM POLE OUTPUT
(±1Amp peak)
p 500kHz OPERATION
A P P L I C AT I O N S
s ECONOMY OFF-LINE FLYBACK OR
FORWARD CONVERTERS
s DC-DC BUCK OR BOOST CONVERTERS
s LOW COST DC MOTOR CONTROL
AVAILABLE OP T I O N S PER PA RT #
Part # Start-Up Hysteresis Max. Duty
Voltage
Cycle
LX1552 16V
6V <100%
LX1553 8.4V 0.8V <100%
LX1554 16V
6V
<50%
LX1555 8.4V 0.8V <50%
T_A (°C)
M
Plastic DIP
8-pin
PACKAGE ORDER INFORMATION
DM
Plastic
8-pin
SOIC
D
Plastic SOIC
14-pin
Y
Ceramic DIP
8-pin
PW
TSSOP
20-pin
0 to 70
-40 to 85
-55 to 125
LX155xCM
LX155xIM
—
LX155xCDM
LX155xIDM
—
LX155xCD
LX155xID
—
—
—
LX155xMY
LX155xCPW
—
—
Note: All surface-mount packages are available in Tape & Reel. Append the letter "T" to part number. (i.e. LX1552CDMT)
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Copyright © 1994
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841
1
Rev. 1.0a 1/01