LT1786F SMBus Programmable CCFL Switching Regulator to-lamp-current control and communicates using the FEATURES 2-wire SMBus serial interface. The LT1786F acts as an n Grounded Lamp or Floating Lamp Configurations SMBus slave device using one of two selectable SMBus n Precision 100m A Full-Scale DAC addresses set by the address pin ADR. Programming Current On Power-up, the DAC output current assumes midrange n 2-Wire SMBus Interface or zero scale, depending on the logic state of the ADR n DAC Setting Is Retained in Shutdown pin.The entire IC can be shut down through the SMBSUS n Wide Battery Input Range: 4.5V to 30V pin or by setting the SHDN bit = 1 in the SMBus command n Open Lamp Protection byte. Digital data for the DAC output current is retained n Two Selectable SMBus Addresses internally and the supply current drops to 40m A for standby U operation. The active low SHDN pin disables the CCFL APPLICATIO S control circuitry, but keeps the DAC alive. Supply current n Notebook and Palmtop Computers in this operating mode drops to 150m A. n Portable Instruments The LT1786F control circuitry operates from a logic supply n Personal Digital Assistants voltage of 3.3V or 5V. The IC also has a battery supply pin that operates from 4.5V to 30V. The LT1786F draws 6mA DESCRIPTIO typical quiescent current. A 200kHz switching frequency The LT 1786F is a fixed frequency, current mode, switch- minimizes magnetic component size. Current mode switch- ing regulator that provides the control function for Cold ing techniques with cycle-by-cycle limiting gives high Cathode Fluorescent Lighting (CCFL). The IC includes an reliability and simple loop frequency compensation. The efficient high current switch, an oscillator, output drive LT1786F is available in a 16-pin narrow SO package. logic, control circuitry and a micropower 6-bit 100m A full- , LTC and LT are registered trademarks of Linear Technology Corporation. scale current output DAC. The DAC provides simple bits- TYPICAL APPLICATIO 90% Efficient Floating CCFL with 2-Wire SMBus Control of Lamp Current CCFL BACKLIGHT APPLICATION CIRCUITS D1 L1 = COILTRONICS CTX210605 CONTAINED IN THIS DATA SHEET ARE COVERED LAMP BAT85 C2 BY U.S. PATENT NUMBER 5408162 L2 = COILTRONICS CTX100-4 27pF AND OTHER PATENTS PENDING *DO NOT SUBSTITUTE COMPONENTS 10 3kV 6 1 16 C5 CCFL COILTRONICS (561) 241-7876 L1 CCFL V SW 1000pF PGND 2 15 32 1 4 5 BAT I BULB CCFL + 8V TO 28V C3B + C3A 14 3 R2 2.2m F 2.2m F DIO BAT 220k C7, 1m F 35V 35V LT1786F 4 13 R1 CCFL V ROYER C C1* 750W 12 5 3V V CC 0.068m F AGND V CC 6.5V + R3 C4 11 6 100k SHUTDOWN SHDN I OUT 2.2m F Q2* Q1* 7 10 SMBSUS SCL 9 8 TO ADR SDA L2 D1 SMBus 100m H 1N5818 HOST 1786F TA01 ALUMINUM ELECTROLYTIC IS RECOMMENDED FOR C3A AND C3B. MAKE 3CB ESR 0.5W TO PREVENT DAMAGE TO THE LT1786F HIGH-SIDE SENSE RESISTOR DUE TO SURGE CURRENTS AT TURN-ON 0m A TO 50m A I CURRENT GIVES FOR ADDITIONAL CCFL/LCD CONTRAST APPLICATION CIRCUITS, CCFL C1 MUST BE A LOW LOSS CAPACITOR, C1 = WIMA MKI OR MKP-20 REFER TO THE LT1182/83/84/84F DATA SHEET 0mA TO 6mA LAMP CURRENT = PANASONIC ECH-U FOR A TYPICAL DISPLAY. Q1, Q2 = ZETEX ZTX849 OR ROHM 2SC5001 1 U ULT1786F UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) V ........................................................................... 7V CC TOP VIEW ORDER PART BAT, Royer, BULB .................................................. 30V 16 CCFL PGND 1 CCFL V SW NUMBER CCFL V ............................................................... 60V SW I 2 15 BULB CCFL Shutdown ................................................................. 6V DIO 3 14 BAT LT1786FCS I Input Current .............................................. 10mA CCFL V 4 13 ROYER CCFL C DIO Input Current (Peak, <100ms).................... 100mA AGND 5 12 V CC Digital Inputs .............................. 0.3V to (V + 0.3V) SHDN 6 11 I OUT CC SMBSUS 7 10 SCL Digital Outputs ............................ 0.3V to (V + 0.3V) CC ADR 8 9 SDA DAC Output Voltage ..................... 15V to (V + 0.3V) CC Junction Temperature (Note 2)............................ 100 C S PACKAGE 16-LEAD PLASTIC SO Operating Ambient Temperature Range ..... 0 C to 70 C T = 100 C, q = 100 C/W JMAX JA Storage Temperature Range ................ 65 C to 150 C Lead Temperature (Soldering, 10 sec)................. 300 C Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25 C. V = SHUTDOWN = SMBSUS = SCL = SDA = 3.3V, A CC BAT = Royer = BULB = 12V, I = CCFL V = Open, DIO = I = GND, CCFL V = 0.5V, unless otherwise specified. CCFL SW OUT C SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS I Supply Current 3V V 6.5V, I = 0m A l 6 9.5 mA Q CC OUT ISUS SMBSUS Supply Current SMBSUS = 0V or Command Code Bit 7 = 1, l 40 100 m A CCFL V = Open (Note 3) C I SHUTDOWN Supply Current SHUTDOWN = 0V, CCFL V = Open (Note 3) l 150 300 m A SHDN C SHUTDOWN Input Bias Current SHUTDOWN = 0V, CCFL V = Open 5 10 m A C SHUTDOWN Threshold Voltage l 0.45 0.85 1.2 V f Switching Frequency Measured at CCFL V , I = 50mA, 175 200 225 kHz SW SW I = 100m A, CCFL V = Open l 160 200 240 kHz CCFL C DC(MAX) Maximum Switch Duty Cycle Measured at CCFL V 80 85 % SW l 75 85 % BV Switch Breakdown Voltage Measured at CCFL V 60 70 V SW Switch Leakage Current V = 12V, Measured at CCFL V 20 m A SW SW V = 30V, Measured at CCFL V 40 m A SW SW I Summing Voltage 3V V 6.5V 0.425 0.465 0.505 V CCFL CC l 0.385 0.465 0.555 V D I Summing Voltage for I = 0m A to 100mA515mV CCFL CCFL D Input Programming Current CCFL V Offset Sink Current CCFL V = 1.5V, Positive Current Measured into Pin 5 5 15 m A C C D CCFL V Source Current for I = 25m A, 50m A, 75m A, 100m A, l 4.70 4.95 5.20 m A/m A C CCFL D I Programming Current CCFL V = 1.5V CCFL C CCFL V to DIO Current Servo Ratio DIO = 5mA out of Pin, Measure I(V ) at CCFL V = 1.5V l 94 99 104 m A/mA C C C CCFL V Low Clamp Voltage V V = BULB Protect Servo Voltage l 0.1 0.3 V C BAT BULB CCFL V High Clamp Voltage I = 100m A l 1.7 2.1 2.4 V C CCFL CCFL V Switching Threshold CCFL V DC = 0% l 0.6 0.95 1.3 V C SW CCFL High-Side Sense Servo Current I = 100m A, I(V ) = 0m A at CCFL V = 1.5V l 0.93 1.00 1.07 A CCFL C C 2 U WWW