LT1241 Series High Speed Current Mode Pulse Width Modulators FEATURES DESCRIPTION n Low Start-Up Current: < 250A The LT 1241 series devices are 8-pin, fixed frequency, n 50ns Current Sense Delay current mode, pulse width modulators. They are improved n Current Mode Operation: To 500kHz plug compatible versions of the industry standard UC1842 n Pin Compatible with UC1842 Series series. These devices have both improved speed and n Undervoltage Lockout with Hysteresis lower quiescent current. The LT1241 series is optimized n No Cross-Conduction Current for off-line and DC/DC converter applications. They con- n Trimmed Bandgap Reference tain a temperature-compensated reference, high gain n 1A Totem Pole Output error amplifier, current sensing comparator and a high n Trimmed Oscillator Frequency and Sink Current current totem pole output stage ideally suited to driv- n Active Pull-Down on Reference and Output During ing power MOSFETs. Start-up current has been reduced Undervoltage Lockout to less than 250A. Cross-conduction current spikes in n High Level Output Clamp: 18V the output stage have been eliminated, making 500kHz n Current Sense Leading Edge Blanking 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 APPLICATIONS oscillator circuit for both frequency and sink current, and n both of these parameters are tightly specified. The out- Off-Line Converters n put stage is clamped to a maximum V of 18V in the DC/DC Converters OUT on state. The output and the reference output are actively All registered trademarks and trademarks are the property of their respective owners. pulled low during undervoltage lockout. BLOCK DIAGRAM UV LOCKOUT REFERENCE ENABLE REFERENCE PULL-DOWN 5V REF 8 V REF MAIN BIAS OUTPUT 7 V PULL-DOWN CC R /C 4 OSCILLATOR T T T 6 OUTPUT S 1 5.6V 1V COMP R 1mA FB 2 5 GND 2R BLANKING 2.5V 18V + R + + 1.5V 3 I SENSE 1241 BD01 Rev B 1 Document Feedback For more information www.analog.comLT1241 Series ABSOLUTE MAXIMUM RATINGS Supply Voltage ..........................................................25V Operating Junction Temperature Range Output Current ........................................................1A* LT124XC ................................................. 0C to 100C Output Energy (Capacitive Load per Cycle) ............... 5J LT124XI ............................................ 40C to 100C Analog Inputs (Pins 2, 3) ............................... 0.3 to 6V LT124XM (Obsolete) ..........................55C to 125C Error Amplifier Output Sink Current .......................10mA Storage Temperature Range ................. 65C to 150C Power Dissipation at T 25C ..................................1W Lead Temperature (Soldering, 10 sec) ...................300C A *The 1A rating for output current is based on transient switching requirements. PIN CONFIGURATION TOP VIEW TOP VIEW COMP 1 V 8 REF COMP 1 8 V REF FB 2 7 V CC FB 2 V 7 CC 3 I 6 OUTPUT SENSE I 3 6 OUTPUT SENSE R /C 4 5 GND T T R /C 4 5 GND T T J8 PACKAGE 8-LEAD CERDIP T = 125C, = 100C/W N8 PACKAGE 8-LEAD PDIP JMAX JA T = 100C, = 130C/W JMAX JA OBSOLETE PACKAGE TOP VIEW COMP 1 8 V REF FB 2 7 V CC I OUTPUT 3 6 SENSE R /C GND 4 5 T T S8 PACKAGE 8-LEAD PLASTIC SO T = 100C, = 150C/W JMAX JA ORDER INFORMATION