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 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
The LX155x family of ultra-low start-up current
(250µA max), current mode control ICs offer new
levels of energy efficiency for offline converter
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.
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.
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 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.
KEY FEATURES
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
High Current Totem Pole Output
(±1A Peak)
500KHz Operation
IMPORTANT:
For the most current data, consult
MICROSEMI’s
website:
http://www.microsemi.com
PRODUCT HIGHLIGHT
Typical Application of LX155x Using Its MicroPower Start-Up Feature
R
ST
AC
INPUT
I
ST
V
CC
LX1552
or
LX1554
NO
OB
TR
EC
SO
OM
L
ME
ET
ND
E P
ED
RO
FO
R
DU
NE
C
W
T
DE
SIG
NS
Design Using
Max. Start-up Current
Specification (I
ST
)
Typical Start-up Resistor
Value (R
ST
)
Max. Start-up Resistor
Power Dissipation (P
R
)
SG384x
1000µA
62KΩ
UC384xA
500µA
LX155x
250µA
124KΩ
1.13W
248KΩ
0.56W
2.26W
Note: Calculation is done for universal AC input
specification of V
ACMIN
= 90V
RMS
to V
ACMAX
= 256V
RMS
using
the following equation: (resistor current is selected to be 2
* I
ST
@ V
ACMIN
)
Part #
APPLICATIONS
Economy Off-Line Flyback or
Forward Converters
DC-DC Buck or Boost Converters
Low Cost DC Motor Control
Available Options Per part#
Start-Up
Max. Duty
Hysteresis
Voltage
Cycle
16V
6V
<100%
8.4V
0.8V
<100%
16V
6V
<50%
8.4V
0.8V
<50%
R
ST
=
V
ACMIN
2 • I
ST
, P
R
=
2V
AC2MAX
R
ST
LX1552
LX1553
LX1554
LX1555
PACKAGE ORDER INFO
T
A
(°C)
0 to 70
-40 to 85
-55 to 125
M
Plastic DIP
8-Pin
LX155xCM
LX155xIM
-
DM
Plastic SOIC
8-Pin
D
Plastic SOIC
14-Pin
Y
Ceramic DIP
8-Pin
PW
Plastic TSSOP
20-Pin
RoHS Compliant / Pb-free
Transition DC: 0503
RoHS Compliant / Pb-free
Transition DC: 0440
RoHS Compliant / Pb-free
Transition DC: 0440
RoHS Compliant / Pb-free
Transition DC: 0442
LX155xCDM
LX155xIDM
-
LX155xCD
LX155xID
-
-
-
LX155xMY
LX155xCPW
-
-
Note: Available in Tape & Reel. Append the letters “TR” to the part number (i.e. LX1552CDM-TR).
Copyright
©
1994
Rev. 1.0b,2005-03-01
L
IN
F
INITY
M
ICROELECTRONICS
I
NC
.
11861 W
ESTERN
A
VENUE
, G
ARDEN
G
ROVE
, CA. 92841, 714-898-8121, F
AX
: 714-893-2570
1
PRODUCT DATABOOK 1996/1997
LX1552/3/4/5
U
LTRA
-L
OW
S
TART
-U
P
C
URRENT
, C
URRENT
-M
ODE
PWM
P
R O D U C T I O N
D
A T A
S
H E E T
A B S O L U T E M A X I M U M R AT I N G S
(Note 1)
PACKAGE PIN OUTS
COMP
V
FB
I
SENSE
R
T
/C
T
1
2
3
4
8
7
6
5
NO
OB
TR
EC
SO
OM
L
ME
ET
ND
E P
ED
RO
FO
R
DU
NE
C
W
T
DE
SIG
NS
COMP
V
FB
I
SENSE
R
T
/C
T
Supply Voltage (Low Impedance Source) .................................................................. 30V
Supply Voltage (I
CC
< 30mA) ......................................................................... Self Limiting
Output Current ............................................................................................................. ±1A
Output Energy (Capacitive Load) ................................................................................ 5µJ
Analog Inputs (Pins 2, 3) ........................................................................... -0.3V to +6.3V
Error Amp Output Sink Current ............................................................................... 10mA
Power Dissipation at T
A
= 25°C (DIL-8) ...................................................................... 1W
Operating Junction Temperature
Ceramic (Y Package) ............................................................................................ 150°C
Plastic (M, DM, D, PW Packages) ........................................................................ 150°C
Storage Temperature Range .................................................................... -65°C to +150°C
Lead Temperature (Soldering, 10 Seconds) ............................................................ 300°C
Pb-free
/ RoHS Peak
Package Solder Reflow Temp. (40 second max. exposure)................ 260°C (+0, -5)
Note 1. Exceeding these ratings could cause damage to the device. All voltages are with respect
to Ground. Currents are positive into, negative out of the specified terminal. Pin
numbers refer to DIL packages only.
V
REF
V
CC
OUTPUT
GND
M & Y PACKAGE
(Top View)
M Package RoHS / Pb-free 100% Matte Tin Lead Finish
1
2
3
4
8
7
6
5
V
REF
V
CC
OUTPUT
GND
DM PACKAGE
(Top View)
RoHS / Pb-free 100% Matte Tin Lead Finish
T H E R M A L D ATA
M PACKAGE:
DM PACKAGE:
D PACKAGE:
Y PACKAGE:
PW PACKAGE:
THERMAL RESISTANCE-JUNCTION TO AMBIENT,
θ
JA
THERMAL RESISTANCE-JUNCTION TO AMBIENT,
θ
JA
THERMAL RESISTANCE-JUNCTION TO AMBIENT,
θ
JA
THERMAL RESISTANCE-JUNCTION TO AMBIENT,
θ
JA
THERMAL RESISTANCE-JUNCTION TO AMBIENT,
θ
JA
95°C/W
165°C/W
120°C/W
130°C/W
144°C/W
COMP
N.C.
V
FB
N.C.
I
SENSE
N.C.
R
T
/C
T
1
2
3
4
5
6
7
14
13
12
11
10
9
8
V
REF
N.C.
V
CC
V
C
OUTPUT
GND
PWR GND
D PACKAGE
(Top View)
N.C.
N.C.
V
REF
N.C.
V
CC
V
C
OUTPUT
GND
PWR GND
N.C.
RoHS / Pb-free 100% Matte Tin Lead Finish
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
Junction Temperature Calculation: T
J
= T
A
+ (P
D
x
θ
JA
).
The
θ
JA
numbers are guidelines for the thermal performance of the device/pc-board system.
All of the above assume no ambient airflow
N.C.
N.C.
COMP
V
FB
N.C.
I
SENSE
N.C.
R
T
/C
T
N.C.
N.C.
PW PACKAGE
(Top View)
RoHS / Pb-free 100% Matte Tin Lead Finish
2
Copyright © 1994
Rev. 1.0b
PRODUCT DATABOOK 1996/1997
LX1552/3/4/5
U
LTRA
-L
OW
S
TART
-U
P
C
URRENT
, C
URRENT
-M
ODE
PWM
P
R O D U C T I O N
D
A T A
S
H E E T
ELECTRICAL
CHARACTERISTICS
Parameter
Reference Section
Output Voltage
Line Regulation
Load Regulation
Temperature Stability (Note 2 & 7)
Total Output Variation
Output Noise Voltage (Note 2)
Long Term Stability (Note 2)
Output Short Circuit
NO
OB
TR
EC
SO
OM
L
ME
ET
ND
E P
ED
RO
FO
R
DU
NE
C
W
T
DE
SIG
NS
Symbol
Test Conditions
V
REF
T
A
= 25°C, I
L
= 1mA
12
≤
V
IN
≤
25V
1
≤
I
O
≤
20mA
V
N
I
SC
Over Line, Load, and Temperature
10Hz
≤
f
≤
10kHz, T
A
= 25°C
T
A
= 125°C, t = 1000hrs
T
A
= 25°C
T
A
= 25°C, R
T
= 698Ω, C
T
= 22nF, LX1552/3 only
12
≤
V
CC
≤
25V
T
MIN
≤
T
A
≤
T
MAX
V
PIN 4
peak to peak
T
A
= 25°C, V
PIN 4
= 2V
V
PIN 4
= 2V, T
MIN
≤
T
A
≤
T
MAX
V
PIN 1
= 2.5V
(Unless otherwise specified, these specifications apply over the operating ambient temperatures for LX155xC with 0°C
≤
T
A
≤
70°C, LX155xI with -40°C
≤
T
A
≤
85°C, LX155xM
with -55°C
≤
T
A
≤
125°C; V
CC
=15V (Note 5); R
T
=10K; C
T
=3.3nF. Low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the
ambient temperature.)
LX155xI/155xM
LX155xC
Units
Min. Typ. Max. Min. Typ. Max.
4.95 5.00 5.05 4.95 5.00 5.05
6
20
6
20
6
25
6
25
0.2 0.4
0.2 0.4
4.9
5.1 4.9
5.1
50
50
5
25
5
25
-30 -100 -180 -30 -100 -180
48.5 50.5 52.5 48.5 50.5 52.5
56
58
60
56
58
60
0.2
1
0.2
1
5
5
1.7
1.7
8.0 8.3 8.6 8.0 8.3 8.6
7.6
8.8 7.8
8.8
2.45 2.50 2.55 2.45 2.50 2.55
-0.1
-1
-0.1 -0.5
65
90
65
90
0.6
0.6
60
70
60
70
2
4
2
4
-0.5 -0.8
-0.5 -0.8
5
6.5
5
6.5
0.7 1.1
0.7 1.1
2.85
0.9
3
1
70
-2
150
3.15 2.85
1.1 0.9
-10
300
0.4
2.2
3
1
70
-2
150
0.1
1.5
13.5
13.5
50
50
0.7
3.15
1.1
-5
300
0.4
2.2
V
mV
mV
mV/°C
V
µV
mV
mA
kHz
kHz
%
%
V
mA
mA
V
µA
dB
MHz
dB
mA
mA
V
V
V/V
V
dB
µA
ns
V
V
V
V
ns
ns
V
Oscillator Section
Initial Accuracy (Note 6)
Voltage Stability
Temperature Stability (Note 2)
Amplitude (Note 2)
Discharge Current
I
D
Error Amp Section
Input Voltage
Input Bias Current
Open Loop Gain
Unity Gain Bandwidth (Note 2)
Power Supply Rejection Ratio (Note 3)
Output Sink Current
Output Source Current
Output Voltage High Level
Output Voltage Low Level
I
B
A
VOL
UGBW
PSRR
I
OL
I
OH
V
OH
V
OL
A
VOL
2
≤
V
O
≤
4V
T
A
= 25°C
12
≤
V
CC
≤
25V
V
PIN 2
= 2.7V, V
PIN 1
= 1.1V
V
PIN 2
= 2.3V, V
PIN 1
= 5V
V
PIN 2
= 2.3V, R
L
= 15K to ground
V
PIN 2
= 2.7V, R
L
= 15K to V
REF
Current Sense Section
Gain (Note 3 & 4)
Maximum Input Signal (Note 3)
Power Supply Rejection Ratio (Note 3)
Input Bias Current
Delay to Output (Note 2)
PSRR
I
B
T
PD
V
OL
V
PIN 1
= 5V
12
≤
V
CC
≤
25V
V
PIN 3
= 0 to 2V
Output Section
Output Voltage Low Level
Output Voltage High Level
Rise Time (Note 2)
Fall Time (Note 2)
UVLO Saturation
V
OH
T
R
T
F
V
SAT
I
SINK
= 20mA
I
SINK
= 200mA
I
SOURCE
= 20mA
I
SOURCE
= 200mA
T
A
= 25°C, C
L
= 1nF
T
A
= 25°C, C
L
= 1nF
V
CC
= 5V, I
SINK
= 10mA
13
12
0.1
1.5
13.5
13.5
50
50
0.7
13
12
100
100
1.2
100
100
1.2
(El ec trica l Char acteris tics contin ue ne xt page .)
Copyright © 1994
Rev. 1.0b
3
PRODUCT DATABOOK 1996/1997
LX1552/3/4/5
U
LTRA
-L
OW
S
TART
-U
P
C
URRENT
, C
URRENT
-M
ODE
PWM
P
R O D U C T I O N
D
A T A
S
H E E T
ELECTRICAL CHARACTERISTICS
Parameter
Symbol
Test Conditions
(Con't.)
Under-Voltage Lockout Section
Start Threshold
NO
OB
TR
EC
SO
OM
L
ME
ET
ND
E P
ED
RO
FO
R
DU
NE
C
W
T
DE
SIG
NS
V
ST
1552/1554
1553/1555
1552/1554
1553/1555
15
7.8
9
7.0
94
47
16
8.4
10
7.6
96
50
48
17
9.0
11
8.2
LX155xI/155xM
LX155xC
Units
Min. Typ. Max. Min. Typ. Max.
15
7.8
9
7.0
94
47
16
8.4
10
7.6
96
50
48
0
150
11
35
250
17
17
9.0
11
8.2
V
V
V
V
%
%
%
%
µA
mA
V
Min. Operation Voltage After Turn-On
PWM Section
Maximum Duty Cycle
1552/1553
1552/1553, R
T
= 698Ω, C
T
= 22nF
1554/1555
Minimum Duty Cycle
Start-Up Current
Operating Supply Current
V
CC
Zener Voltage
0
Power Consumption Section
I
ST
I
CC
V
Z
I
CC
= 25mA
30
150
11
35
250
17
30
Notes: 2. These parameters, although guaranteed, are not 100% tested in
production.
3. Parameter measured at trip point of latch with V
FB
= 0.
∆
V
4. Gain defined as: A =
∆
V
COMP
; 0
≤
V
ISENSE
≤
0.8V.
ISENSE
5. Adjust V
CC
above the start threshold before setting at 15V.
6. Output frequency equals oscillator frequency for the LX1552 and
LX1553. Output frequency is one half oscillator frequency for the
LX1554 and LX1555.
7. Temperature stability, sometimes referred to as average temperature
coefficient, is described by the equation:
Temp Stability =
V
REF
(max.) - V
REF
(min.)
T
A
(max.) - T
A
(min.)
V
REF
(max.) & V
REF
(min.) are the maximum & minimum reference
voltage measured over the appropriate temperature range. Note that the
extremes in voltage do not necessarily occur at the extremes in
temperature.
BLOCK DIAGRAM
V
CC
*
34V
UVLO
S/R
GROUND**
5V
REF
V
REF
16V (1552/1554)
8.4V (1553/1555)
16V (1552/1554)
8.4V (1553/1555)
INTERNAL
BIAS
V
REF
GOOD LOGIC
V
C
*
R
T
/C
T
OSCILLATOR
***
T
OUTPUT
ERROR AMP
2R
S
V
FB
COMP
I
SENSE
R
1V
R
PWM
LATCH
POWER GROUND**
CURRENT SENSE
COMPARATOR
* - V
CC
and V
C
are internally connected for 8 pin packages.
** - POWER GROUND and GROUND are internally connected for 8 pin packages.
*** - Toggle flip flop used only in 1554 and 1555.
4
Copyright © 1994
Rev. 1.0b
PRODUCT DATABOOK 1996/1997
LX1552/3/4/5
U
LTRA
-L
OW
S
TART
-U
P
C
URRENT
, C
URRENT
-M
ODE
PWM
P
R O D U C T I O N
D
A T A
S
H E E T
GRAPH / CURVE INDEX
FIGURE INDEX
FIGURE #
1.
2.
3.
4.
5.
6.
7.
8.
9.
OSCILLATOR FREQUENCY vs. TIMING RESISTOR
MAXIMUM DUTY CYCLE vs. TIMING RESISTOR
OSCILLATOR FREQUENCY vs. TEMPERATURE
OUTPUT DUTY CYCLE vs. TEMPERATURE
OSCILLATOR DISCHARGE CURRENT vs. TEMPERATURE
OUTPUT INITIAL ACCURACY vs. TEMPERATURE
REFERENCE VOLTAGE vs. TEMPERATURE
E.A. INPUT VOLTAGE vs. TEMPERATURE
REFERENCE SHORT CIRCUIT CURRENT vs. TEMPERATURE
10.
START-UP CURRENT vs. TEMPERATURE
11.
START-UP CURRENT vs. SUPPLY VOLTAGE
12.
START-UP CURRENT vs. SUPPLY VOLTAGE
13.
DYNAMIC SUPPLY CURRENT vs. OSCILLATOR FREQUENCY
14.
CURRENT SENSE DELAY TO OUTPUT vs. TEMPERATURE
16.
START-UP THRESHOLD vs. TEMPERATURE
17.
START-UP THRESHOLD vs. TEMPERATURE
15.
CURRENT SENSE THRESHOLD vs. ERROR AMPLIFIER OUTPUT
18.
MINIMUM OPERATING VOLTAGE vs. TEMPERATURE
19.
MINIMUM OPERATING VOLTAGE vs. TEMPERATURE
20.
LOW LEVEL OUTPUT SATURATION VOLTAGE DURING UNDER-
VOLTAGE LOCKOUT
21.
OUTPUT SATURATION VOLTAGE vs. OUTPUT CURRENT and
TEMPERATURE
22.
OUTPUT SATURATION VOLTAGE vs. OUTPUT CURRENT and
TEMPERATURE
Copyright © 1994
Rev. 1.0b
NO
OB
TR
EC
SO
OM
L
ME
ET
ND
E P
ED
RO
FO
R
DU
NE
C
W
T
DE
SIG
NS
FIGURE #
FIGURE #
30.
CURRENT SENSE SPIKE SUPPRESSION
31.
MOSFET PARASITIC OSCILLATIONS
34.
SLOPE COMPENSATION
35.
OPEN LOOP LABORATORY FIXTURE
36.
OFF-LINE FLYBACK REGULATOR
Characteristic Curves
Theory of Operation Section
23.
TYPICAL APPLICATION OF START-UP CIRCUITRY
24.
REFERENCE VOLTAGE vs. TEMPERATURE
25.
SIMPLIFIED SCHEMATIC OF OSCILLATOR SECTION
26.
DUTY CYCLE VARIATION vs. DISCHARGE CURRENT
27.
OSCILLATOR FREQUENCY vs. TIMING RESISTOR
28.
MAXIMUM DUTY CYCLE vs. TIMING RESISTOR
29.
CURRENT SENSE THRESHOLD vs. ERROR AMPLIFIER OUTPUT
Typical Applications Section
32.
ADJUSTABLE BUFFERED REDUCTION OF CLAMP LEVEL
WITH SOFT-START
33.
EXTERNAL DUTY CYCLE CLAMP AND MULTI-UNIT SYCHRONIZATION
5
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