LT1768 High Power CCFL Controller for Wide Dimming Range and Maximum Lamp Lifetime DESCRIPTIO FEATURES TM n Ultrawide Multimode Dimming Range The LT 1768 is designed to control single or multiple cold n Multiple Lamp Capability cathode fluorescent lamp (CCFL) displays. A unique Mul- n Programmable PWM Dimming Range and timode Dimming scheme* combines both linear and PWM Frequency control functions to maximize lamp life, efficiency, and n Precision Maximum and Minimum Lamp dimming range. Accurate maximum and minimum lamp Currents Maximize Lamp Lifetime currents can be easily set. The LT1768 can detect and n No Lamp Flicker Under All Supply and Load protect against lamp failures and overvoltage start-up Conditions conditions. It is designed to provide maximum flexibility n Open Lamp Detection and Protection with a minimum number of external components. n 350kHz Switching Frequency The LT1768 is a current mode PWM controller with a 1.5A n 1.5A MOSFET Gate Driver MOSFET driver for high power applications. It contains a n 100mV Current Sense Threshold 350kHz oscillator, 5V reference, and a current sense n 5V Reference Voltage Output comparator with a 100mV threshold. It operates from an n The 16-Lead SSOP Package 8V to 24V input voltage. The LT1768 also has undervoltage U lockout, thermal limit, and a shutdown pin that reduces APPLICATIO S supply current to 65A. It is available in a small 16-lead n Desktop Flat Panel Displays SSOP package. n Multiple Lamp Displays , LTC and LT are registered trademarks of Linear Technology Corporation. Multimode Dimming is a trademark of Linear Technology Corporation. n Notebook LCD Displays *Patent Pending n Point of Sale Terminal Displays TYPICAL APPLICATIO 33pF LAMP C4-WIMA MKP2 L1-COILTRONICS UP4-680 610 T1-2 CTX110607 IN PARALLEL LAMP Q1-ZDT1048 T1 33pF V *R5 CAN BE METAL PCB TRACE IN 8V 24V 4 53 2 1 Lamp Output and Dimming C1 C4 Ratio vs Lamp Current 33m F 0.33m F 10000 PGND GATE DI02 V IN 1000 250 5V DIMMING RATIO (NITS/NITS) 1/4W DI01 V REF Q1 Q1 0.1m F 100 SENSE FAULT LAMP OUTPUT (NITS) LT1768 V C SHDN 10 C2 L1 0.033m F AGND R 68m H MIN R4 MBRS130T3 16.2k 1 R2 C R T MAX 40.2k LAMP MANUFACTURERS C3 SPECIFIED CURRENT RANGE 0.1m F Si3456DY PROG PWM 0.1 PROG 100 0 2 4 6 8 10 0V TO 5V OR R3 LAMP CURRENT (mA) C4 1kHz PWM R1 60.4k R5* 10m F 2200pF 1768 TA01b 49.9k 0.025 1768 TA01 Figure 1. 14W CCFL Supply Produces a 100:1 Dimming Ratio While Maintaining Minimum and Maximum Lamp Current Specifications 1 U ULT1768 UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) Input Voltage (V Pin) ............................................ 28V ORDER PART IN TOP VIEW SHDN Pin Voltage .................................................... 28V NUMBER PGND 1 16 GATE FAULT Pin Voltage ................................................... 28V DI01 2 15 V IN PROG Pin Voltage ................................................... 5.5V LT1768CGN DI02 3 14 V REF PWM Pin Voltage.................................................... 4.5V LT1768IGN SENSE 4 13 FAULT C Pin Voltage ........................................................ 4.5V T VC 5 12 SHDN SENSE Pin Voltage .................................................... 1V AGND 6 11 R MIN GN PART DIO1, DIO2 Input Current ................................... 50mA C 7 10 R T MAX MARKING R Pin Source Current ..................................... 750A MAX PROG 8 9 PWM R Pin Source Current ..................................... 750A MIN GN PACKAGE 1768 V Pin Source Current ....................................... 10mA REF 16-LEAD PLASTIC SSOP 1768I Operating Junction Temperature Range T = 125C, = 100C/W JMAX JA LT1768C ................................................ 0C to 125C LT1768I ............................................ 40C to 125C Consult LTC Marketing for parts specified with wider operating temperature ranges. Storage Temperature Range ................. 65C to 150C Lead Temperature (Soldering 10 sec)................... 300C ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25C, V = 12V, I = 250A, V = 0V, V = 2.5V, I = 100A, A VIN DIO1/2 PROG PWM RMAX I = 100A, unless otherwise specified. RMIN SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS I Supply Current 9V< V < 24V l 78 mA Q VIN I Supply Current in Shutdown V = 0V l 65 100 A SHDN SHDN SHDN Pin Pull-Up Current V = 0V l 47 12 A SHDN SHDN Threshold Voltage V Off to On l 0.6 1.26 1.8 V SHDN SHDN Threshold Hysteresis l 100 200 300 mV V Undervoltage Lockout V Off to On l 7.2 7.9 8.2 V IN IN V Undervoltage Lockout V On to Off l 7.1 7.4 7.6 V IN IN V REF Voltage I = 1mA l 4.9 5 5.1 V REF REF REF Line Regulation V 8V to 24V I = 1mA l 720 mV VIN REF REF Load Regulation I 1mA to 10mA l 10 20 mV REF V R Pin Voltage l 1.225 1.25 1.275 V RMAX MAX V R Pin Voltage l 1.22 1.26 1.30 V RMIN MIN FSW Switching Frequency V = 0.75V, V = 0V l 300 350 410 kHz PROG SENSE Maximum Duty Cycle V = 0.75V, V = 0V 93 % PROG SENSE Minimum ON Time V = 0.75V, V = 150mV 125 ns PROG SENSE I PROG Pin Input Bias Current V = 5V l 100 500 nA PROG PROG V PROG Pin Voltage for Zero Lamp Current (Note 2) l 0.45 0.5 0.55 V PROG PROG Pin Voltage for Minimum Lamp Current (Note 3) l 0.9 1 1.1 V PROG Pin Voltage for Maximum Lamp Current (Note 4) l 3.8 4 4.2 V 2 U WWW