LT1244IS8 Datasheet, PDF (1/16 Pages) Linear Technology – High Speed Current Mode Pulse Width Modulators

FEATURES
s _{Low Start-Up Current: < 250µA}
s _{50ns Current Sense Delay}
s _{Current Mode Operation: To 500kHz}
s _{Pin Compatible with UC1842 Series}
s _{Undervoltage Lockout with Hysteresis}
s _{No Cross-Conduction Current}
s _{Trimmed Bandgap Reference}
s _{1A Totem Pole Output}
s _{Trimmed Oscillator Frequency and Sink Current}
s _{Active Pull-Down on Reference and Output During}
Undervoltage Lockout
s _{High Level Output Clamp: 18V}
s _{Current Sense Leading Edge Blanking}
APPLICATI S
s _{Off-Line Converters}
s _{DC/DC Converters}
, LTC and LT are registered trademarks of Linear Technology Corporation.
LT1241 Series
High Speed Current Mode
Pulse Width Modulators
DESCRIPTIO
The LT^®1241 series devices are 8-pin, fixed frequency,
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 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 V_OUT of 18V in the
on state. The output and the reference output are actively
pulled low during undervoltage lockout.
BLOCK DIAGRA
R_T/C_T 4
COMP 1
FB 2
–
2.5V
+
I_SENSE 3
OSCILLATOR
5.6V
1mA
2R
1V
–
R
+
5V REF
MAIN BIAS
REFERENCE ENABLE
REFERENCE PULL-DOWN
UV
LOCKOUT
OUTPUT
PULL-DOWN
T
S
R
BLANKING
18V
+
1.5V
–
8 V_REF
7 V_CC
6 OUTPUT
5 GND
1241 BD01
1