current mode, pulse width modulators. They are improved
plug compatible versions of the industry standard UC1842
series. These devices have both improved speed and
lower quiescent current. The LT1241 series is optimized
for off-line and DC/DC converter applications. They con-
tain a temperature-compensated reference, high gain
error amplifier, current sensing comparator and a high
current totem pole output stage ideally suited to driv-
ing power MOSFETs. Start-up current has been reduced
to less than 250µA. Cross-conduction current spikes in
the output stage have been eliminated, making 500kHz
operation practical. Several new features have been incor-
porated. Leading edge blanking has been added to the
current sense comparator. Trims have been added to the
oscillator circuit for both frequency and sink current, and
both of these parameters are tightly specified. The out-
put stage is clamped to a maximum V
OUT
of 18V in the
on state. The output and the reference output are actively
pulled low during undervoltage lockout.
n
n
Low Start-Up Current: < 250µA
50ns Current Sense Delay
Current Mode Operation: To 500kHz
Pin Compatible with UC1842 Series
Undervoltage Lockout with Hysteresis
No Cross-Conduction Current
Trimmed Bandgap Reference
1A Totem Pole Output
Trimmed Oscillator Frequency and Sink Current
Active Pull-Down on Reference and Output During
Undervoltage Lockout
High Level Output Clamp: 18V
Current Sense Leading Edge Blanking
APPLICATIONS
n
n
Off-Line Converters
DC/DC Converters
All registered trademarks and trademarks are the property of their respective owners.
BLOCK DIAGRAM
REFERENCE ENABLE
5V REF
MAIN BIAS
REFERENCE PULL-DOWN
OUTPUT
PULL-DOWN
T
1V
S
R
6
OUTPUT
UV
LOCKOUT
8
7
V
REF
V
CC
R
T
/C
T
COMP
FB
4
5.6V
1mA
2
2.5V
OSCILLATOR
1
–
+
2R
R
–
+
BLANKING
5
18V
GND
+
1.5V
I
SENSE
3
–
1241 BD01
Rev B
Document Feedback
For more information
www.analog.com
1
LT1241 Series
ABSOLUTE MAXIMUM RATINGS
Supply Voltage ..........................................................25V
Output Current ........................................................± 1A*
Output Energy (Capacitive Load per Cycle) ............... 5µJ
Analog Inputs (Pins 2, 3) ............................... –0.3 to 6V
Error Amplifier Output Sink Current .......................10mA
Power Dissipation at T
A
≤
25°C..................................1W
Operating Junction Temperature Range
LT124XC................................................. 0°C to 100°C
LT124XI ............................................ – 40°C to 100°C
LT124XM
(Obsolete)
.......................... – 55°C to 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
*The 1A rating for output current is based on transient switching
requirements.
PIN CONFIGURATION
TOP VIEW
COMP
FB
I
SENSE
R
T
/C
T
1
2
3
4
8
7
6
5
V
REF
V
CC
OUTPUT
GND
TOP VIEW
COMP
FB
I
SENSE
R
T
/C
T
1
2
3
4
8
7
6
5
V
REF
V
CC
OUTPUT
GND
J8 PACKAGE 8-LEAD CERDIP
T
JMAX
= 125°C,
θ
JA
= 100°C/W
OBSOLETE PACKAGE
TOP VIEW
COMP 1
FB 2
I
SENSE
3
R
T
/C
T
4
8
7
6
5
V
REF
V
CC
OUTPUT
GND
N8 PACKAGE 8-LEAD PDIP
T
JMAX
= 100°C,
θ
JA
= 130°C/W
S8 PACKAGE 8-LEAD PLASTIC SO
T
JMAX
= 100°C,
θ
JA
= 150°C/W
ORDER INFORMATION
LEAD FREE FINISH
LT124XCJ8#PBF
LT124XCN8#PBF
LT124XCS8#PBF
LT124XIN8#PBF
LT124XIS8#PBF
LT124XMJ8#PBF
TAPE AND REEL
LT124XCJ8#TRPBF
LT124XCN8#TRPBF
LT124XCS8#TRPBF
LT124XIN8#TRPBF
LT124XIS8#TRPBF
LT124XMJ8#TRPBF
http://www.linear.com/product/LT1241#orderinfo
PART MARKING*
124X
124X
124X
124XI
124XI
PACKAGE DESCRIPTION
8-Lead CERDIP
8-Lead PDIP
8-Lead Plastic SO
8-Lead PDIP
8-Lead Plastic SO
OBSOLETE PACKAGE
8-Lead CERDIP
–55°C to 125°C
TEMPERATURE RANGE
0°C to 100°C
0°C to 100°C
0°C to 100°C
–40°C to 125°C
–40°C to 125°C
OBSOLETE PACKAGE
Consult ADI Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
Rev B
2
For more information
www.analog.com
LT1241 Series
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Notes 2 and 3)
PARAMETER
Reference Section
Output Voltage
Line Regulation
Load Regulation
Temperature Stability
Total Output Variation
Output Noise Voltage
Long Term Stability
Output Short-Circuit Current
Oscillator Section
Initial Accuracy
Voltage Stability
Temperature Stability
Amplitude
Clock Ramp Reset Current
Error Amplifier Section
Feedback Pin Input Voltage
Input Bias Current
Open-Loop Voltage Gain
Unity-Gain Bandwidth
Power Supply Rejection Ratio
Output Sink Current
Output Source Current
Error Amplifier Section
Output Voltage High Level
Output Voltage Low Level
Current Sense Section
Gain
Maximum Current Sense Input Threshold
Power Supply Rejection Ratio
Input Bias Current
Delay to Output
Blanking Time
Blanking Override Voltage
V
PIN3
< 1.1V
l
l
l
l
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
4.925
l
l
TYP
5.000
3
–6
0.1
MAX
5.075
20
–25
5.13
UNITS
V
mV
mV
mV/°C
V
µV
mV
mA
kHz
kHz
%
%/°C
V
I
O
= 1mA, T
J
= 25°C
12V < V
CC
< 25V
1mA < I
VREF
< 20mA
Line, Load, Temp
10Hz < F < 10kHz, T
J
= 25°C
T
A
= 125°C, 1000 Hrs
l
l
4.87
50
5
–30
47.5
228
–90
50
248
– 0.05
1.7
7.9
8.2
2.50
90
1.3
6
–0.75
5.6
0.2
2.85
0.90
3.00
1.00
70
–1
50
100
1.5
25
–180
52.5
268
1
R
T
= 10k, C
T
= 3.3nF, T
J
= 25°C
R
T
= 13.0k, C
T
= 500pF, T
J
= 25°C
12V < V
CC
< 25V, T
J
= 25°C
T
MIN
< T
J
< T
MAX
T
J
= 25°C (Pin 4)
V
OSC
(Pin 4) = 2V, T
J
= 25°C
V
PIN1
= 2.5V
V
FB
= 2.5V
2 < V
O
< 4V
T
J
= 25°C
12V < V
CC
< 25V
V
PIN2
= 2.7V, V
PIN1
= 1.1V
V
PIN2
= 2.3V, V
PIN1
= 5V
V
PIN2
= 2.3V, R
L
= 15k to GND
V
PIN2
= 2.7V, R
L
= 15k to Pin 8
l
l
l
l
l
l
8.5
2.58
–2
mA
V
µA
dB
MHz
dB
mA
mA
V
2.42
65
0.7
60
2
–0.5
5
2
l
l
1.1
3.15
1.10
10
100
V
V/V
V
dB
µA
ns
ns
V
Rev B
For more information
www.analog.com
3
LT1241 Series
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Notes 2 and 3)
PARAMETER
Output Section
Output Low Level
Output High Level
Rise Time
Fall Time
Output Clamp Voltage
Undervoltage Lockout
Start-Up Threshold
LT1241
LT1242/LT1244
LT1243/LT1245
Minimum Operating Voltage
LT1241/LT1243/LT1245
LT1242/LT1244
Hysteresis
LT1241
LT1242/LT1244
LT1243/LT1245
PWM
Maximum Duty Cycle
LT1241/LT1244/LT1245
LT1242/LT1243
Minimum Duty Cycle
Total Device
Start-Up Current
Operating Current
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
l
l
l
l
l
l
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
I
OUT
= 20mA
I
OUT
= 200mA
I
OUT
= 20mA
I
OUT
= 200mA
MIN
l
l
l
l
TYP
0.25
0.75
MAX
0.4
2.2
UNITS
V
V
V
V
12.0
11.75
50
30
80
60
19.5
C
L
= 1nF, T
J
= 25°C
C
L
= 1.0nF, T
J
= 25°C
I
O
= 1mA
l
ns
ns
V
18
9.0
15
7.8
7.0
9.0
1.6
5.5
0.4
9.6
16
8.4
7.6
10
2.0
6.0
0.8
10.2
17
9.0
8.2
11
V
V
V
V
V
V
V
V
T
J
= 25°C
T
J
= 25°C
l
46
94
48
96
0
170
7
250
10
%
%
%
µA
mA
Note 2:
Unless otherwise specified, V
CC
= 15V, R
T
= 10k, C
T
= 3.3nF.
Note 3:
Low duty cycle pulse techniques are used during test to maintain
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PCB Design
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