LT1241 Series
High Speed Current Mode
Pulse Width Modulators
U
DESCRIPTIO
EATURE
S
F
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
The LT®1241 series devices are 8-pin, fixed frequency,
currentmode,pulsewidthmodulators.Theyareimproved
plugcompatibleversionsoftheindustrystandardUC1842
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 er-
ror amplifier, current sensing comparator and a high
current totem pole output stage ideally suited to driving
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 output
stage is clamped to a maximum VOUT of 18V in the
on state. The output and the reference output are actively
pulled low during undervoltage lockout.
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Trimmed Bandgap Reference
1A Totem Pole Output
Trimmed Oscillator Frequency and Sink Current
Active Pull-Down on Reference and Output During
Undervoltage Lockout
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High Level Output Clamp: 18V
Current Sense LeO adU ing Edge Blanking
PPLICATI
S
A
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Off-Line Converters
DC/DC Converters
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, LTC and LT are registered trademarks of Linear Technology Corporation.
W
BLOCK DIAGRA
UV
LOCKOUT
REFERENCE ENABLE
REFERENCE PULL-DOWN
5V REF
MAIN BIAS
8
7
V
V
REF
CC
OUTPUT
PULL-DOWN
4
OSCILLATOR
R /C
T
T
T
6
5
OUTPUT
GND
S
R
5.6V
1
2
1V
COMP
FB
1mA
–
+
2R
BLANKING
1.5V
–
+
2.5V
18V
R
+
3
I
SENSE
–
1241 BD01
1