LINEAR TECHNOLOGY LT1182/LT1183/LT1184/LT1184F Manual
Contents
1. FBP Input Bias Current vs Temperature 171182 G35 0 03 1 0 5 0 9 0 025 amp Lr 0 020 go 06 0 015 05 5 04 9 ee ae a 0 005 E 02 t 0 1 U mcum gm p TU E 75 50 25 0 25 50 75 100125 150 175 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C TEMPERATURE C LT1182 629 LT1182 630 FBN Input Bias Current FBP to LCD Vc Transconductance vs Temperature vs Temperature 3 0 1300 1200 25 E lt 1100 20 gt 1000 a a 15 S 900 TT PPS z m lt 22 800 5 700 2 05 600 E 0 500 75 50 25 0 25 50 75 100 125 150 175 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C TEMPERATURE C LT1182 G32 171182 633 LT1183 REF Output Impedance LT1184 84F REF Output vs Temperature Impedance vs Temperature 70 30 5 s 60 5 25 55 gt 50 2 2 5 45 a gt 5 40 i 15 3 th Bi 35 m 30 10 5 5 20 5 75 50 25 0 25 50 75 100 125 150 175 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C TEMPERATURE C LT1182 G36 LT1182 LT1183 LT1 184 LT1 1845 TYPICAL PERFORMANCE CHARACTERISTICS LCD Vsw Sat Voltage vs Switch Current CCFL Vsw S2. 6 n lt ca E 4 s 5 2 ca TEMPERATURE C 171182 G21 CCFL High Side Sense Null Current Line Regulation vs Temperature 000 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C 111182 G24 Bulb Input Bias Current vs Temperature 0 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C LT1182 G27 LY 7 11182 1171183 111184 111184 TYPICAL PERFORMANCE CHARACTERISTICS LCD FBP Reference vs Temperature 1 274 1 264 1 254 1 244 1 234 LCD FBP REFERENCE VOLTAGE V 1 224 1 214 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C LT1182 G28 LCD FBN Offset Voltage vs Temperature 17 21 23 LCD FBN OFFSET VOLTAGE mV I e 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C FBN to LCD Vc Transconductance vs Temperature 1200 1100 1000 900 800 700 D 600 500 FBN TO LCD TRANSCONDUCTANCE umhos 400 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C LT1182 G34 FBP Reference Voltage Line Regulation vs Temperature
3. e 75 85 BV Switch Breakdown Voltage Measured at CCFL Vsw and LCD Vsw 60 70 V Switch Leakage Current Vsw 12V Measured at CCFL Vsw and LCD Vsw 20 uA Vsw 30V Measured at CCFL Vsw and LCD Vsw 40 uA Summing Voltage 3V lt Vin lt 30V Measured on LT1182 LT1183 0 41 0 45 0 49 V e 037 045 0 54 V 3V lt Vin lt 30V Measured on LT1184 LT1184F 0 425 0 465 0 505 V e 0385 0 465 0 555 V Summing Voltage for lccri to 1004A 5 15 mV Alnput Programming Current CCFL Offset Sink Current CCFL Vg 1 5V Positive Current Measured into Pin 5 5 15 pA ACCFL Vc Source Current for locr 25uA 50uA 75 100pA e 470 495 5 20 uA uA Programming Current CCFL V 1 5V CCFL Vc to DIO Current Servo Ratio DIO 5mA out of Pin Measure lyc at CCFL Vc 1 5V e 94 99 104 uA mA CCFL Vc Low Clamp Voltage Vpat Vpuig Bulb Protect Servo Voltage e 0 1 0 3 V CCFL Vc High Clamp Voltage 100A e 17 2 1 24 V CCFL Vc Switching Threshold CCFL Vsw DC 0 e 06 0 95 1 3 V CCFL High Side Sense Servo Current Icer 1O0uA Ivc OpA at CCFL Vc 1 5V e 0 93 100 1 07 A CCFL High Side Sense Servo Current BAT 5V to 30V 100pA 0 1 0 16 V Line Regulation lyc OpA at CCFL Vc 1 5V CCFL High Side Sense Supply Current Current Measured into BAT and Royer Pins e 50 100 150 pA Bulb Protect Servo Voltage 100pA 0uA at CCFL Vc 1 5V e 65 7 0 7 5 V Servo Voltage Measured Between BAT and Bulb Pins Bul
4. FEATURES Wide Input Voltage Range 3V to 30V Low Quiescent Current High Switching Frequency 200kHz CCFL Switch 1 25A LCD Switch 625mA Grounded or Floating Lamp Configurations Open Lamp Protection Positive or Negative Contrast Capability APPLICATIONS Notebook and Palmtop Computers m Portable Instruments m Automotive Displays Retail Terminals TECHNOLOGY LT1182 LT1183 LT1184 LT1 1 84F CCFL LCD Contrast owitching Regulators DESCRIPTION The LT 1182 LT1183 are dual current mode switching regulators that provide the control function for Cold Cath ode Fluorescent Lighting CCFL and Liquid Crystal Display LCD Contrast The LT1184 LT1184F provide only the CCFL function The ICs include high current high efficiency switches an oscillator a reference output drive logic control blocks and protection circuitry The LT1182 per mits positive or negative voltage LCD contrast operation The LT1183 permits unipolar contrast operation and pins out an internal reference The LT1182 LT1183 support grounded and floating lamp configurations The LT1184F supports grounded and floating lamp configurations The LT1184 supports only grounded lamp configurations The Z LTC and LT are registered trademarks of Linear Technology Corporation TYPICAL APPLICATION 90 Efficient Floating CCFL Configuration with Dual Polarity LCD Contrast ALUMINUM ELECTROLYTIC IS RECOMMENDED FOR C3B WITH AN ESR gt 0 5Q TO PREVENT D
5. PIN V PWM cone OV TO 5V 1kHz PWM 10 to 100 DC 22uF SOMA R1 R2 AND R3 ARE IDEAL VALUES USE NEAREST 1 VALUE 1182 11 LY LT1182 L11183 LT1184 LT1 1845 TYPICAL APPLICATIONS LY LT1182 LCD Contrast Positive Boost Converter BAT 8V TO 28V L3 50uH COILTRONICS CTX50 4 POSCON Vout 2 Vin LT1182 i R12 ROYER 20k R13 8 45k 1 R14 121k 1 1182 TA12 LT1182 LCD Contrast Positive Boost Charge Pump Converter BAT 8V TO 28V 50uH COILTRONICS CTX50 4 POSCON Vout 2 Vin LT1182 i R12 CCFL Vc ROYER 20k R13 8 45k 1 R14 1 21k 1182 13 Information furnished by Linear Technology Corporation is believed to be accurate and reliable However no responsibility is assumed for its use Linear Technology Corporation makes no represen tation that the interconnection of its circuits as described herein will not infringe on existing patent rights 11182 1171183 111184 111184 TYPICAL APPLICATIONS LT1182 LCD Contrast Positive to Negative Charge Pump Converter BAT 8V TO 28V COILTRONICS CTX50 4 011 22uF D5 35V 1N914 NEGCON gt Vin 1182 14 RELATED PARTS PART NUMBER FREQUENCY SWITCH CURRENT DESCRIPTION LT1107 63kHz 1A Micropower DC DC Converter for LCD Contrast Control Hysteretic LT1172 100kHz 1 25A Current Mode Switching Regulator for CCFL o
6. amplifier concept entirely and replace it with a lamp current programming block This block provides an easy to use interface to program lamp current The program mer circuit also reduces the number of time constants in the control loop by combining the error signal conversion scheme and frequency compensation into a single capaci tor The control loop thus exhibits the response of a single pole system allows for faster loop transient response and virtually eliminates overshoot under startup or overload conditions Lamp current is programmed at the input of the program mer block the pin This pin is the input of a shunt regulator and accepts a DC input current signal of OuA to 100A This input signal is converted to a to 500uA source currentatthe CCFL Vc pin The programmer circuit is simply a current to current converter with a gain of five By regulating the pin the input programming current can be set with DAC PWM or potentiometer control The typical input current programming range for OmA to 6mA lamp current is to 50 The pin is sensitive to capacitive loading and will oscillate with capacitance greater than 10pF For example loading the pin with a 1x or 10x scope probe causes oscillation and erratic CCFL regulator operation because of the probe s respective input capacitance A current meter in series with the pin will also produce oscil lation due to its shunt c
7. 6 75 50 25 0 25 50 75 100125 150 175 TEMPERATURE C LT1182 G22 CCFL High Side Sense Supply Current vs Temperature 150 140 130 120 110 eee T 60 CCFL HIGH SIDE SENSE SUPPLY CURRENT uA 50 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C LT1182 G25 1 00 0 09 0 08 0 07 0 06 0 05 0 04 0 03 0 02 0 10 LCD Vc LOW CLAMP VOLTAGE V LCD Vc Low Clamp Voltage vs Temperature 0 75 50 25 0 25 50 75 100 125 _ 1 060 1 040 1 020 1 000 0 980 0 960 CCFL HIGH SIDE SENSE NULL CURRENT A 0 940 TEMPERATURE C 111182 G20 CCFL High Side Sense Null Current vs Temperature 2 4 2 3 2 2 2 1 2 0 1 9 LDC V HIGH CLAMP VOLTAGE V 1 8 1 7 LCD Vc High Clamp Voltage vs Temperature 75 50 25 0 25 50 75 100 125 150 175 0 160 0 140 75 50 25 0 25 50 75 100 125 150 175 BULB PROTECT SERVO VOLTAGE V TEMPERATURE C LT1182 G23 Bulb Protect Servo Voltage vs Temperature 6 5 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C LT1182 G26 0 120 0 100 0 080 0 060 0 040 0 020 CCFL HIGH SIDE SENSE LINE REGULATION V 10 a 8 LLI
8. 7 70 Ps 10 6 60 oe Vin 30 9 5 5 50 e Vin 7 a Viu 5V 3 3 7 3 5 30 Vin 6 2 20 5 1 10 4 0 0 75 50 25 0 25 50 75 100 125 150 175 75 50 25 0 25 50 75 100 125 150 175 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C TEMPERATURE C TEMPERATURE C 111182 601 171182 602 171182 603 Shutdown Input Bias Current Shutdown Threshold Voltage vs Temperature vs Temperature CCFL Frequency vs Temperature 6 1 2 5 T 230 220 E I 5 4 S 10 E 97 Vin 5V 25 210 T vw 30V IN E WI L c 09 200 5 ui Vin 3V LL z Vin 3V 08 ae g o 2 180 1 2 0 7 170 0 0 6 160 75 50 25 0 25 50 75 100 125 150 175 75 50 25 0 25 50 75 100125 150 175 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C TEMPERATURE C TEMPERATURE C 111182 604 111182 605 171182 606 CCFL Duty Cycle vs Temperature LCD Frequency vs Temperature LCD Duty Cycle vs Temperature 95 240 95 93 230 93 91 91 z 220 89 s 89 o 87 5 210 Viy 30V d 87 85 5 85 ae Vin 3V a 83 E 190 a 83 m a 5 81 S is 81 79 79 7 170 77 160 75 75 50 25 0 25 50 75 100 125 150 175 75 50 25 0 25 50 75 100 125 150 175 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C TEMPERATURE C TEMPERATURE C 171182 607 171182 608 171182 609 5 11182 1171183 111184 111184 TYPICAL PERFORMANCE CHARACTER
9. CCFL Vsw NUMBER lccrL BULB lccrL BULB DIO BAT DIO BAT CCFL Vc NC 11118405 CCFL Vc ROYER 171184605 AGND VIN AGND VIN SHUTDOWN REF SHUTDOWN REF NC NC NC NC Nc 8 NC NC NC KAGE 16 LEAD PLASTIC SO 16 LEAD PLASTIC SO Tumax 100 C 0 ja 100 C W Tymax 100 C 100 C W Consult factory for Industrial and Military grade parts 2 LY LT1182 LT1183 LT1 184 LT1 1 84F ELECTRICAL CHARACTERISTICS Ta 25 C Vy 5V BAT Royer Bulb 12V SHUTDOWN CCFL Open DIO GND CCFL Ve 0 5V LT1182 LT1183 LCD Vc 0 5V LCD Vsw Open LT1182 FBN FBP GND LT1183 FB GND LT1183 LT1184 LT1184F REF Open unless otherwise specified SYMBOL PARAMETER CONDITIONS MIN TYP UNITS lq Supply Current LT1182 LT1183 3V lt Vin lt 30V e 9 14 mA LT1184 LT1184F 3V lt Vin lt 30V 6 9 5 mA ISHDN SHUTDOWN Supply Current SHUTDOWN OV CCFL Vc LCD Vc Open Note 2 35 70 SHUTDOWN Input Bias Current SHUTDOWN OV CCFL Vc LCD Vc Open 3 6 pA SHUTDOWN Threshold Voltage e 06 0 85 1 2 V 1 Switching Frequency Measured at CCFL Vsw and LCD Vow 50mA 175 200 225 kHz 100uA CCFL Vc Open LT1182 FBN FBP 1V LT1183 FB 1V LT1182 LT1183 LCD Vc Open e 160 200 240 kHz DC MAX Maximum Switch Duty Cycle Measured at CCFL Vsw and LCD Vsw 80 85
10. CCFL switch current flows through this pin and permits internal switch current sensing The regulators provide a separate analog ground and power ground s to isolate high current ground paths from low current signal paths Linear Technology recommends the use of star ground layout techniques lccri Pin 2 This pin is the input to the CCFL lamp current programming circuit This pin internally regulates to 450mV LT1182 LT1183 or 465mV LT1184 LT1184F The pin accepts a DC input current signal of OuA to 100uA full scale This input signal is converted to a to 500pA source current at the CCFL Vc pin By shunt regulating the pin the input programming current can be set with DAC PWM or potentiometer control As input program ming current increases the regulated lamp current in creases For a typical 6mA lamp the range of input programming current is about OuA to 50uA DIO Pin 3 This pin is the common connection between the cathode and anode of two internal diodes The remain ing terminals of the two diodes connect to ground In a grounded lamp configuration DIO connects to the low voltage side of the lamp Bidirectional lamp current flows in the DIO pin and thus the diodes conduct alternately on half cycles Lamp current is controlled by monitoring one half of the average lamp current The diode conducting on negative half cycles has one tenth of its current diverted to the CCFL Vc pin This current nulls against the
11. 1kHz PWM fa ce 171183 2 2uF L Vc SHUTDOWN R9 4 99k 1 C10 als 0 1 uF R11 40 2k V CONTRAST R10 10k 1 1 OV TO 5V T x TTE 0 01uF I 1182 TA02 20 AL MIR LT1182 LT1183 LT1 184 LT1184F TYPICAL APPLICATIONS LT1184F Floating CCFL with Potentiometer Control of Lamp Current UP TO 6mA ALUMINUM ELECTROLYTIC IS RECOMMENDED FOR C3B WITH AN LAMP ESR gt 0 50 TO PREVENT DAMAGE TO THE LT1184F HIGH SIDE C2 SENSE RESISTOR DUE TO SURGE CURRENTS AT TURN ON Hd C1 MUST BE A LOW LOSS CAPACITOR C1 WIMA MKP 20 10 6 01 02 ZETEX ZTX849 OR ROHM 2505001 L1 COILTRONICS CTX210605 BAT L2 COILTRONICS CTX100 4 8V TO 28V DO NOT SUBSTITUTE COMPONENTS COILTRONICS 407 241 7876 TO 45pA IccrL CURRENT GIVES OMA TO 6mA LAMP CURRENT FOR A TYPICAL DISPLAY 35V L2 D1 100uH 1N5818 LT1184F LVc ROYER VIN gt 3V 7 SHUTDOWN 2 2uF R4 R5 T 15 4k 50k 1 10 TURN 1182 TA03 21 11182 1171183 111184 111184 TYPICAL APPLICATIONS LT1182 LT1183 IccFL PWM Programming V PWM R1 R2 OVTO5V 40 5k 40 5k 1kHz PWM TO Iccp PIN 0 to 90 DC to 50uA 1 AND R2 ARE IDEAL VALUES IN 22uF USE NEAREST 1 VALUE 1182 TA04 LT1184 LT1184F IccFL PWM Programming V PWM R1 R2 OVTO5V 40 35k 40 35k 1kHz PWM TO Iocr PIN 0 to 90 DC i OpA to 50uA c1 R1 AND R2 ARE IDEAL VALUES T 2 2uF USE NEAREST 1 VALU
12. 3V Vin 30V LCD Vc 0 8V e 0 00 003 V FBP FB Input Bias Current LT1182 FBP REF1 FBN 1V LCD Vc 0 8V 171183 REF1 LCD Vc 0 8V 0 35 1 0 pA LCD FBN FB Offset Voltage 171182 Measured at FBN Pin FBP OV LCD Vc 0 8V 20 12 4 mV LT1183 Measured at FB Pin LCD Vc 0 8V e 27 12 1 mV Offset Voltage Line Regulation 3V lt Vin 30V LCD 0 8V e 0 01 0 2 V FBN FB Input Bias Current LT1182 FBN 0ffset Voltage FBP 0V LCD Vc 0 8V LT1183 FB Offset Voltage LCD Vc 0 8V e 30 10 m FBP FB to LCD Transconductance 171182 Alyc 25 FBN 1V 650 900 1150 umhos LT1183 Alyc 25pA e 500 900 1300 umhos FBN FB to LCD Vc Transconductance LT1182 Alyc 25 FBP GND 550 800 1050 umhos LT1183 Alyc 25pA e 400 800 1200 umhos LCD Error Amplifier Source Current LT1182 FBP FBN 1V or 0 25V e 50 100 175 171183 FB 1V or 0 25V LCD Error Amplifier Sink Current LT1182 FBP FBN 1 5V or 0 25V e 35 100 175 171183 FB 1 5V or 0 25V LCD Vc Low Clamp Voltage 171182 FBP FBN 1 5V LT1183 FB 1 5V 0 01 0 3 V LCD Vc High Clamp Voltage 171182 FBP FBN 1V LT1183 FB 1V 1 7 2 0 2 4 V LCD Vc Switching Threshold LT1182 FBP FBN 1V LT1183 FB 1V Vsw DC 0 0 6 0 95 1 3 V LCD Switch Current Limit Duty Cycle 50 e 0 625 1 00 1 5 A Duty Cycle 75 Note 3 e 0400 0 85 1 3 A VsAT2 LCD Switch On Resistance LCD law 0 5A e 1 0 1 65 Q Alg Su
13. 84 BLOCK DIAGRAM LT1184 LT1184F CCFL Regulator Top Level Block Diagram VIN UNDER SHUTDOWN 6 SHUTDOWN E DM AGND LT1184 LT1184F REFERENCE IS BROUGHT OUT TO PIN 1 PINS 7 8 9 10 ARE NO CONNECT VOLTAGE LOCKOUT 200kHz OSC BAT ROYER LT1184 HIGH SIDE SENSE RESISTOR R4 AND GM AMPLIFIER ARE REMOVED PIN 13 IS NO CONNECT CCFL Vsw LOGIC 1 DRIVE 1 0 10 a GAIN 4 4 CCFL Vc PGND 1184 BD02 APPLICATIONS INFORMATION Introduction Current generation portable computers and instruments use backlit Liquid Crystal Displays LCDs These displays also appear in applications extending to medical equip ment automobiles gas pumps and retail terminals Cold Cathode Fluorescent Lamps CCFLs provide the highest available efficiency in backlighting the display Providing the mostlight out for the least amount of input power is the most important goal These lamps require high voltage AC to operate mandating an efficient high voltage DC AC converter The lamps operate from DC but migration effects damage the lamp and shorten its lifetime Lamp drive should contain zero DC component In addition to good efficiency the converter should deliver the lamp drive in the form of a sine wave This minimizes EMI and RF emissions Such emissions can interfere with other devices and can also degrade overall operating efficiency Sinusoidal CCFL drive maximizes current to li
14. AMAGE TO THE LT1182 HIGH SIDE SENSE RESISTOR DUE TO SURGE CURRENTS AT TURN ON C1 MUST BE A LOW LOSS CAPACITOR C1 WIMA MKP 20 01 02 ZETEX ZTX849 OR ROHM 25 5001 L1 COILTRONICS CTX210605 L2 COILTRONICS CTX100 4 L3 COILTRONICS CTX02 12403 DO NOT SUBSTITUTE COMPONENTS COILTRONICS 407 241 7876 OpA TO 45pA ICCFL CURRENT GIVES OmA TO 6mA BULB CURRENT THIS IS EQUAL TO 0 TO 90 DUTY 05 CYCLE FOR THE PWM SIGNAL V PWM OV TO 5V IKHZPWM 22uF LT1182 CCFL ROYER SHUTDOWN CCFL BACKLIGHT APPLICATION CIRCUITS CONTAINED IN THIS C2 DATA SHEET ARE COVERED BY U S PATENT NUMBER 5408162 27pF AND OTHER PATENTS PENDING BAT 8V TO 28V EITHER NEGCON OR POSCON MUST BE GROUNDED GROUNDING NEGCON GIVES VARIABLE POSITIVE CONTRAST FROM 10V TO 30V GROUNDING POSCON GIVES VARIABLE NEGATIVE CONTRAST FROM 10V TO 30V POSCON NEGCON 1182 3 TAO1 L11182 LT1183 LT1 184 LT1 184F DESCRIPTION LT1184 LT1184F pin out the reference for simplified pro gramming of lamp current The LT1182 LT1183 LT1184 LT1184F operate with input supply voltages from 3V to 30V The ICs also have a battery supply voltage pin that operates from 4 5V to 30V The LT1182 LT1183 draw 9mA typical quiescent current while the LT1184 LT1184F draw 6mA typical quiescent current An active low shutdown pin typically reduces total supply current to 35uA for standby operation A 200kHz s
15. E 1182 TAOS LT1183 Programming with Potentiometer Control R1 R2 15 9k 50k VREF TO PIN R1 AND R2 ARE IDEAL VALUES USE NEAREST 1 VALUE 1182 TA06 lccrL 120A TO 50uA LT1184 LT1184F IccFL Programming with Potentiometer Control R1 R2 15 5k 50k VREF TO PIN R1 AND R2 ARE IDEAL VALUES USE NEAREST 1 VALUE 1182 TA07 12uA TO 50uA LT1182 LT1183 LT1184 LT1184F IccFL Programming with DAC Control R1 5k TO PIN L STRAY OUTPUT T CAPACITANCE CURRENT SOURCE DAC R1 DECOUPLES THE DAC OUTPUT CAPACITANCE FROM THE Iccet PIN 1182 TA12 22 171183 IccFL PWM Programming with VREF FROM VREF V PWM R1 0V TO 5V 01 3300 1kHz PWM VN2222L 0 to 90 DC to 50uA 7 15k TO PIN Ul R1 PREVENTS OSCILLATION R2 AND R3 ARE IDEAL VALUES USE NEAREST 1 VALUE 1182 TA08 LT1184 LT1184F IccFL PWM Programming with VREF FROM VREF V PWM R1 0V TO 5V 01 3300 1kHz PWM VN2222L 0 to 90 DC to 50nA TO PIN Ul R1 PREVENTS OSCILLATION R2 AND R3 ARE IDEAL VALUES USE NEAREST 1 VALUE 1182 TA09 LT1183 Iccr PWM Programming with VREF FROM VREF TO Iccp PIN V PWM CCFL OV TO 5V 1kHz PWM 10 to 100 DC VN2222L 22uF SOHA TO OWA R1 R2 AND R3 ARE IDEAL VALUES USE NEAREST 1 VALUE 1182 10 LT1184 LT1184F Iccr PWM Programming with VREF TO
16. ISTICS lccrL Summing Voltage Summing Voltage 95 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C LT1182 616 vs Temperature Load Regulation 5 4 CES ET E 5 1 55 m 0 I amp 5 a a cu 5 72 25 C m zo i 4 o 5 5 a 5 T 125 C 6 e e gt 2 7 lt g 5 0 38 0 75 50 25 0 25 50 75 100 125 150 175 0 20 40 60 80 100 120 140 160 180 200 TEMPERATURE C PROGRAMMING CURRENT pA 171182 G10 171182 611 ACCFL Source Current for Alccri Programming Current Positive DIO Voltage vs Temperature vs Temperature 5 10 12 a T 5 05 1 0 EE so 100A 08 5 5 a oo o o 495 IccrL 50pA o 06 S e o 10A m i lt gt gt OE 490 04 25 e c5 cc a c 1 g 485 02 80 0 75 50 25 0 25 50 75 100125 150 175 75 50 25 0 25 50 75 100125 150 175 TEMPERATURE C TEMPERATURE C 171182 613 171182 G14 CCFL to DIO Current Servo CCFL Vc Low Clamp Voltage Ratio vs Temperature vs Temperature 103 0 30 E lt 31 0 25
17. L transformer Evaluations of loop compensation for over shoot on startup transients and overload conditions are essential to avoid destructive arcing overheating and transformer failure Open lamp conditions force the Royer converter to operate open loop Component stress is again worst case with maximum input voltage conditions The LT1182 LT1183 LT1184 LT1184F open lamp pro tection clamps the maximum transformer secondary volt age to safe levels and transfers the regulator loop from current mode operation into voltage mode operation Other fault conditions include board shorts and compo nent failures These fault conditions can increase primary side currents to very high levels especially at maximum input voltage conditions Solutions to these fault condi tions include electrical and thermal fuses in the supply voltage trace Improvements in battery technology are increasing bat tery lifetimes and decreasing battery voltages required by the portable systems However operation at reduced battery voltages requires higher turns ratio transformers forthe CCFL to generate equivalent output drive capability The penalty incurred with high ratio transformers is higher circulating currents acting on the same primary side components Loss terms increase and electrical efficiency often decreases 19 APPLICATIONS INFORMATION Size Constraints Tighter length width and height constraints for CCFL and LCD contrast cont
18. T1184 LT1184F REF Pin 11 This pin brings outthe 1 244V reference Its functions include the programming of negative contrast voltages with an external resistor divider network LT1183 only and the programming of lamp current for the pin LTC does not recommend using the REF pin for both functions at once The REF pin has a typical output impedance of 45Q on the LT1183 and a typical output impedance of 15Q on the LT1184 LT1184F Reference load current should be limited to a few hundred microam peres otherwise reference regulation will be degraded REF is used to generate the maximum programming current for the pin by placing a resistor between the pins PWM or DAC control subtracts from the maximum programming current Asmall decoupling capacitor 0 1uF is recommended to filter switching transients 12 LY LT1182 L11183 LT1184 LT1 1845 BLOCK DIAGRAM LT1182 LT1183 CCFL LCD Contrast Regulator Top Level Block Diagram VIN BAT ROYER 12 14 13 SHUTDOWN 240 SHUTDOWN 6 REGULATOR UNDER THERMAL VOLTAGE sHUTDOWN LOCKOUT CCFL Vsw Vsw s 200kHz OSC 01 RA LOGIC 1 DRIVE 1 R1 ANTI SAT1 0 1250 GAIN 4 4 gt 5 L7 LCD LCD ICCFL AGND DIO BULB CCFL CCFL PGND Vc PGND LT1183 FBP AND FBN ARE TIED TOGETHER T0 CREATE FB 10 THE REFERENCE IS BROUGHT OUT TO PIN 11 13 11182 1171183 111184 1111
19. andard switching configura tions and is used as a classic DC DC converter The dual input stage error amplifier easily regulates either positive or negative contrast voltages Topology choices for the converter include single inductor and transformer based solutions The switching regulator operates equally well either in continuous mode or discontinuous mode Effi ciencies for LCD contrast circuits range from 75 to 85 and depend on the total power drain of the particular display Adjustment control of the LCD contrast voltage is provided by either potentiometer PWM or DAC control LT1182 LT1183 LT1 184 LT1 1845 Applications Support Linear Technology invests an enormous amount of time resources and technical expertise in understanding de signing and evaluating backlight LCD contrast solutions for system designers The design of an efficient and compact LCD backlight system is a study of compromise in a transduced electronic system Every aspect of the design is interrelated and any design change requires complete re evaluation for all other critical design param eters Linear Technology has engineered one of the most complete test and evaluation setups for backlight designs and understands the issues and tradeoffs in achieving a compact effficient and economical customer solution Linear Technology welcomes the opportunity to discuss design evaluate and optimize any backlight LCD contrast system with a customer For further inf
20. apacitance Use a decoupling resistor of several kilo ohms between the pin and the control circuitry if excessive stray capacitance exists This is basically free with potentiometer or PWM control as these control schemes use resistors A current output DAC should use an isolating resistor as the DAC can have significant output capacitance that changes as a function of input code Grounded Lamp Configuration In a grounded lamp configuration the low voltage side of the lamp connects directly to the LT1182 LT1183 LT1184 LT1184F DIO pin This pin is the common connection between the cathode and anode of two internal diodes In previous grounded lamp solutions these diodes were discrete units and are now integrated onto the IC saving cost and board space Bi directional lamp current flows in the DIO pin and thus the diodes conduct alternately on half 16 LY APPLICATIONS INFORMATION cycles Lamp current is controlled by monitoring one half of the average lamp current The diode conducting on negative half cycles has one tenth of its current diverted to the CCFL pin and nulls against the source current provided by the lamp current programmer circuit The compensa tion capacitor on the CCFL Vc pin provides stable loop compensation and an averaging function to the rectified sinusoidal lamp current Therefore input programming current relates to one half of average lamp current The transfer function between lamp curren
21. at Voltage vs Switch Current CCFL Vsw SAT VOLTAGE V LCD Vey CURRENT LIMIT A T 25 C I T 125 C A 5 C 0 0 3 0 6 0 9 1 2 1 5 SWITCH CURRENT A LT1182 G37 LCD Vsw Current Limit vs Duty Cycle 1 2 0 9 25 C 125 06 MINIMUM 0 3 0 0 10 20 30 40 50 60 70 80 90 DUTY CYCLE 171182 G40 LCD VSW SAT VOLTAGE V FORCED BETA 0 0 3 0 6 0 9 1 2 1 5 SWITCH CURRENT A 171182 638 Forced Beta vs lsw CCFL Vsw 110 100 90 80 70 60 50 40 30 20 10 0 0 02 04 06 08 10 12 14 16 18 2 0 CCFL lgw A LT1182 641 CCFL Vsw CURRENT LIMIT A FORCED BETA 2 5 155 a 2 a o CCFL Vsw Current Limit vs Duty Cycle 25 C T 125 C MINIMUM 0 0 10 20 30 40 50 60 70 80 90 100 90 80 70 60 50 40 30 20 10 DUTY CYCLE LT1182 G39 Forced Beta vs lsw LCD 0 0 02 04 0 6 0 8 1 0 12 1 4 1 6 1 8 2 0 LCD lgw 171182 642 11182 1171183 111 184 111184 PIN FUNCTIONS LT1182 LT1183 LT1184 LT1184F CCFL PGND Pin 1 This pin is the emitter of an internal NPN power switch
22. b Input Bias Current 100pA OA at CCFL Vc 1 5V 5 9 pA loin CCFL Switch Current Limit Duty Cycle 50 e 125 1 9 3 0 A Duty Cycle 75 Note 3 e 09 1 6 2 6 A Vsatt CCFL Switch On Resistance CCFL Isy e 0 6 1 0 Q Alg Supply Current Increase During CCFL law 20 30 mA A Alsw1 CCFL Switch On Time VREF Reference Voltage Measured at REF Pin 11 on LT1183 LT1184 LT1184F 1224 1244 1 264 V e 1214 1244 1 274 V Reference Output Impedance Measured at REF Pin 11 on LT1183 e 20 45 70 Q Measured at REF Pin 11 on LT1184 LT1184F 5 15 30 Q LY CO 11182 1171183 111184 111184 ELECTRICAL CHARACTERISTICS 25 C Vin 5V BAT Royer Bulb 12V SHUTDOWN CCFL Vsw Open DIO GND CCFL Ve 0 5V LT1182 LT1183 LCD Vc 0 5V LCD Vsw Open LT1182 FBN FBP GND LT1183 GND LT1183 LT1184 LT1184F REF Open unless otherwise specified SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Vrer Summing Voltage Measured on LT1183 0 760 0 795 0 830 V e 0 725 0 795 0 865 V Vrer Summing Voltage Measured on LT1184 LT1184F 0 740 0 775 0 810 V e 0 705 0 775 0 845 V REF1 LCD FBP FB Reference Voltage 171182 Measured at FBP Pin FBN 1V LCD Vc 0 8V 1 224 1 244 1 264 V LT1183 Measured at FB Pin LCD Vc 0 8V e 1 214 1244 1 274 V REF1 Voltage Line Regulation
23. c 101 lt S 100 8 020 d 9 gg 015 2 s 98 8 2 lt 5 005 gt c 96 o 8 5 lt gt 0 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C 171182 G17 CCFL Offset Sink Current vs Temperature 10 9 8 CCFL 1 5V 7 6 5 CCFL 1 0V 4 3 2 1 0 CCFL V 0 5V 1 2 3 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C 171182 612 Negative 010 Voltage vs Temperature 1 4 010 10mA 1 2 10 010 5mA 0 8 010 1mA 0 6 0 4 0 2 0 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C LT1182 615 CCFL Vc High Clamp Voltage vs Temperature 24 2 3 2 2 2 1 2 0 1 9 1 8 14 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C LT1182 G18 LY LT1182 LT1183 LT1 184 LT1 1845 TYPICAL PERFORMANCE CHARACTERISTICS CCFL Switching Threshold Voltage vs Temperature CCFL V SWITCHING THRESHOLD VOLTAGE V 0 6 75 50 25 0 25 50 75 100 125 150 175 TEMPERATURE C LCD Vc Switching Threshold Voltage vs Temperature 1 3 0 7 LDC Vc SWITCHING THRESHOLD VOLTAGE V 0
24. ent signal paths Linear Technology recom mends star ground layout techniques LY 11 11182 1171183 111184 111184 FUNCTIONS LCD Vsw Pin 9 This pin is the collector of the internal NPN power switch for the LCD contrast regulator The power switch provides a minimum of 625mA Maximum switch current is a function of duty cycle as internal slope compensation ensures stability with duty cycles greater than 50 Using a driver loop to automatically adapt base drive current to the minimum required to keep the switch in a quasi saturation state yields fast switching times and high efficiency operation The ratio of switch current to driver current is about 50 1 LT1182 FBN Pin 10 This pin is the noninverting terminal for the negative contrast control error amplifier The inverting terminal is offset from ground by 12mV and defines the error amplifier output state under start up conditions The FBN pin acts as a Summing junction for a resistor divider network Input bias current for this pin is typically 1A flowing out of the pin If this pin is not used force FBN to greater than 0 5V to deactivate the negative contrast control input stage The proximity of FBN to the LCD Vow pin makes it sensitive to ringing on the switch pin A small capacitor 0 01uF from FBN to ground filters switching ripple FBP Pin 11 This pin is the inverting terminal for the positive contrast control error amplifier The noninv
25. erting terminal is tied to an internal 1 244V reference Input bias current for this pin is typically 0 5uA flowing into the pin Ifthis pinis not used ground FBP to deactivatethe positive contrast control input stage The proximity of FBP to the LCD Vsw pin makes it sensitive to ringing on the switch pin A small capacitor 0 01uF from FBP to ground filters switching ripple LT1183 FB Pin 10 This pin isthe common connection between the noninverting terminal for the negative contrast error amplifier and the inverting terminal for the positive con trast error amplifier In comparison to the LT1182 the FBN and the FBP pins tie together and come outas one pin This scheme permits one polarity of contrast to be regulated The proximity of FB to the LCD Vow pin makes it sensitive to ringing on the switch pin A small capacitor 0 01 pF from FB to ground filters switching ripple The FB pin requires attention to start up conditions when generating negative contrast voltages The pin has two stable operating points regulating to 1 244V for positive contrast voltages or regulating to 12mV for negative contrast voltages Under start up conditions the FB pin heads to a positive voltage If negative contrast voltages are generated tie a diode from the FB pin to ground This ensures that the FB pin will clamp before reaching the positive reference voltage Switching action then pulls the FB pin back to its normal servo voltage LT1183 L
26. etween the BAT and Bulb pins This circuit sets the maximum voltage level across the primary side of the Royer converter under all operating conditions and limits the maximum secondary output under start up conditions or open lamp conditions This eases transformer voltage rating requirements Set the voltage limit to insure lamp start up with worst case lamp Start voltages and cold temperature system operating conditions The Bulb pin connects to the junction of an external divider network The divider network connects from the center tap of the Royer transformer or the actual battery supply voltage to the top side of the current source tail inductor A capacitor across the top of the divider network filters switching ripple and sets a time constant that determines how quickly the clamp activates When the comparator activates sink current is generated to pull the CCFL Vc pin down This action transfers the entire regulator loop from current mode operation into voltage mode operation BAT Pin 14 This pin connects to the battery or battery charger voltage from which the CCFL Royer converter and LCD contrast converter operate This voltage is typically higher than the Viy supply voltage but can be equal or less than Viy However the BAT voltage must be at least 2 1V greater than the internal 2 4V regulator or 4 5V minimum up to 30V maximum This pin provides biasing for the lamp current programming block is used with the Royer pin for
27. floating lamp configurations and connects to one input for the open lamp protection circuitry For floating lamp configurations this pin is the noninverting terminal of a high side current sense amplifier The typical quies cent current is 5OpA into the pin The BAT and Royer pins monitor the primary side Royer converter current through aninternal 0 1Q top side currentsense resistor A OA to 1A primary side center tap converter current is translated to an input signal range of 0mV to 100mV for the current sense amplifier This input range translates to a OuA to 500uA sink current atthe CCFL Vc pin that nulls againstthe source current provided by the programmer circuit The BAT pin also connects to the top side of an internal clamp between the BAT and Bulb pins LT1182 LT1183 LT1 184 LT1 1845 Royer Pin 13 This pin connects to the center tapped primary of the Royer converter and is used with the BAT pin in a floating lamp configuration where lamp current is controlled by sensing Royer primary side converter cur rent This pin is the inverting terminal of a high side current sense amplifier The typical quiescent current is 50uA into the pin If the CCFL regulator is not used in a floating lamp configuration tie the Royer and BAT pins together This pin is only available on the LT1182 LT1183 LT1184F Vin Pin 12 This pin is the supply pin for the LT1182 LT1183 LT1184 LT1184F The ICs acceptan input voltage range of 3V minimum to 30V
28. g frequency of 60kHz 1pF of stray capacitance represents an impedance of 2 65MQ With an operating lamp voltage of 400V and an operating lamp current of 6mA the parasitic current is 150uA The efficiency loss is 2 5 Layout techniques that increase parasitic capaci LT1182 LT1183 LT1 184 LT1 1 8AF tance include long high voltage lamp leads reflective metal foil around the lamp and displays supplied in metal enclosures Losses for a good display are under 5 whereas losses for a bad display range from 5 to 25 Lossy displays are the primary reason to use a floating lamp configuration Providing symmetric differential drive to the lamp reduces the total parasitic loss by one half Maintaining closed loop control of lamp current in a floating lamp configuration now necessitates deriving a feedback signal from the primary side of the Royer trans former Previous solutions have used an external preci sion shunt and high side sense amplifier configuration This approach has been integrated onto the LT1182 LT1183 LT1184F for simplicity of design and ease of use An internal 0 1W resistor monitors the Royer converter current and connects between the input terminals of a high side sense amplifier A to Royer primary side center tap current is translated to a OuA to 500uA sink current at the CCFL Vc pin to null against the source current provided by the lamp current programmer circuit The compensation capacitor on the CCFL Vc pin
29. ght conver sion in the lamp The circuit should also permit lamp intensity control from zero to full brightness with no hysteresis or pop on 14 LY APPLICATIONS INFORMATION Manufacturers offer a wide array of monochrome and color displays LCD display types include passive matrix and active matrix These displays differ in operating volt age polarity positive and negative contrast voltage dis plays operating voltage range contrast adjust range and power consumption LCD contrast supplies must regu late provide output adjustment over a significant range operate over a wide input voltage range and provide load currents from milliamps to tens of milliamps The small size and battery powered operation associated with LCD equipped apparatus dictate low component count and high efficiency for these circuits Size con Straints place severe limitations on circuit architecture and long battery life is a priority Laptop and handheld portable computers offer an excellent example The CCFL and its power supply are responsible for almost 50 of the battery drain Displays found in newer color machines can have acontrast power supply battery drainas highas 20 Additionally all components including PC board and hard ware usually must fit within the LCD enclosure with a height restriction of 5mm to 10mm The CCFL switching regulator in the LT1182 LT1183 LT1184 LT1184F typically drives an inductor that acts as aswi
30. ides excellent rejec tion of input voltage variations Second it reduces the 90 phase shift at mid frequencies in the energy storage inductor This simplifies closed loop frequency compen sation under widely varying input voltage or output load conditions Finally it allows simple pulse by pulse cur rent limiting to provide maximum switch protection under output overload or short circuit conditions The LT1182 LT1183 LT1184 LT1184F incorporate a low dropout internal regulator that provides a 2 4V supply for most of the internal circuitry This low dropout design allows input voltage to vary from 3V to 30V with little 15 11182 1171183 111184 111184 APPLICATIONS INFORMATION change in quiescent current An active low shutdown pin typically reduces total supply current to 5 by shutting off the 2 4V regulator and locking out switching action for standby operation The ICs incorporate undervoltage lock out by sensing regulator dropout and locking out switch ing below about 2 5V The regulators also provide thermal shutdown protection that locks out switching in the pres ence of excessive junction temperatures A200kHz oscillator is the basic clock for all internal timing The oscillator turns on an output via its own logic and driver circuitry Adaptive anti sat circuitry detects the onset of saturation in a power switch and adjusts base drive current instantaneously to limit switch saturation This mini
31. ltages to be generated with minor circuit changes The difference between the LT1182 and LT1183 is found in the pinout for the inputs of the LCD contrast error amplifier The LT1182 brings out the error amplifier inputs individually for setting up positive and negative polarity contrast capability This feature allows an output connector to determine the choice of contrast operating polarity by a ground connection The LT1183 ties the error amplifier inputs together and brings out an internal refer ence The reference may be used in generating negative contrast voltages or in programming lamp current Block Diagram Operation TheLT1182 LT1183 LT1184 LT1184Farefixed frequency current mode switching regulators Fixed frequency cur rent mode switchers control switch duty cycle directly by switch current rather than by output voltage Referring to the block diagram for the LT1182 LT1183 the switch for each regulator turns ON atthe start of each oscillator cycle The switches turn OFF when switch current reaches a predetermined level The operation of the CCFL regulator in the LT1184 LT1184F is identical to that in the LT1182 LT1183 The control of output lamp current is obtained by using the output of a unique programming block to set current trip level The contrast voltage is controlled by the output of a dual input stage error amplifier which sets current trip level The current mode switching technique has several advantages First it prov
32. maximum with little change in quiescent current zero switch current An internal low dropout regulator provides a 2 4V supply for most of the internal circuitry Supply current increases as switch current increases at a rate approximately 1 50 of switch current This corresponds to a forced Beta of 50 for each switch The ICs incorporate undervoltage lockout by sens ing regulator dropout and lockout switching for input voltages below 2 5V Hysteresis is not used to maximize the useful range of input voltage The typical input voltage is a 3 3V or 5V logic supply LT1182 LT1183 LCD V Pin 7 This pin is the output of the LCD contrast error amplifier and the input of the current comparator for the LCD contrast regulator Its uses include frequency compensation and current limiting The voltage on the LCD Vg pin determines the current trip level for switch turnoff During normal operation this pin sits at a voltage between 0 95V zero switch current and 2 0V maximum switch current The LCD Vc pin has a high impedance output and permits external voltage clamping to adjust current limit A series R C network to ground provides stable loop compensation LCD PGND Pin 8 This pin is the emitter of an internal NPN power switch LCD contrast switch current flows through this pin and permits internal switch current sensing The regulators provide a separate analog ground and power ground s to isolate high current ground paths from low curr
33. mizes driver dissipation and provides rapid turn off of the switch The CCFL power switch is guaranteed to provide a minimum of 1 25A in the LT1182 LT1183 LT1184 LT1184F and the LCD power switch is guaranteed to provide a minimum of 0 625A in the LT1182 LT1183 The anti sat circuitry provides a ratio of switch current to driver current of about 50 1 Simplified Lamp Current Programming A programming block in the LT1182 LT1183 LT1184 LT1184Fcontrols lamp current permitting either grounded lamp or floating lamp configurations Grounded configu rations control lamp current by directly controlling one half of actual lamp current and converting it to a feedback signal to close a control loop Floating configurations control lamp current by directly controlling the Royer s primary side converter current and generating a feedback signal to close a control loop Previous backlighting solutions have used a traditional error amplifier in the control loop to regulate lamp current This approach converted an RMS current into a DC voltage for the input of the error amplifier This approach used several time constants in order to provide stable loop frequency compensation This compensation scheme meant that the loop had to be fairly slow and that output overshoot with startup or overload conditions had to be carefully evaluated in terms of transformer stress and breakdown voltage requirements The LT1182 LT1183 LT1184 LT1184F eliminate the error
34. o lytic for the transformer center tap bypass capacitor with an ESR greater than or equal to 0 50 This lowers the peak Surge currents to an acceptable level In general the wire and trace inductance in this path also help reduce the di dt of the surge current This issue only exists with floating lamp circuits as grounded lamp circuits do not make use of the high side sense resistor Optimizing Optical Efficiency vs Electrical Efficiency Evaluating the performance of an LCD backlight requires the measurement of both electrical and photometric effi ciencies The best optical efficiency operating point does not necessarily correspond to the best electrical effi ciency However these two operating points are generally close The desired goal is to maximize the amount of light out for the least amount of input power It is possible to construct backlight circuits that operate with over 90 electrical efficiency but produce significantly less light Output than circuits that operate at 80 electrical effi ciency The best electrical efficiency typically occur s just as the CCFL s transformer drive waveforms begin to exhibit artifacts of higher order harmonics reflected back from the Royer transformer secondary Maximizing electrical effi ciency equates to smaller values for the Royer primary Side resonating capacitor and larger values for the Royer secondary side ballast capacitor The best optical effi ciency occurs with nearly ideal
35. ormation on back light LCD contrast designs consult the references listed below References 1 Williams Jim August 1992 Illumination Circuitry for Liquid Crystal Displays Linear Technology Corporation Application Note 49 2 Williams Jim August 1993 Techniques for 92 Effi cient LCD Illumination Linear Technology Corporation Application Note 55 3 Bonte Anthony March 1995 LT1182 Floating CCFL with Dual Polarity Contrast Linear Technology Corpora tion Design Note 99 4 Williams Jim April 1995 A Precision Wideband Cur rent Probe for LCD Backlight Meaasurement Linear Tech nology Corporation Design Note 101 LY 19 LT1182 LT1183 LT1 184 LT1184F TYPICAL APPLICATIONS 90 Efficient Grounded CCFL Configuration with Negative Polarity LCD Contrast UP TO 6mA C1 MUST BE A LOW LOSS CAPACITOR LAMP C1 WIMA MKP 20 01 02 ZETEX ZTX849 OR ROHM 2565001 L1 COILTRONICS CTX210605 L2 COILTRONICS CTX100 4 L3 COILTRONICS CTX02 12403 DO NOT SUBSTITUTE COMPONENTS C5 COILTRONICS 407 241 7876 1000pF BAT 8V TO 28V VARYING THE V CONTRAST VOLTAGE FROM OV TO 5V GIVES VARIABLE NEGATIVE CONTRAST FROM 10V TO 30V THE CURRENT REQUIRED FOR AN RMS BULB CURRENT IS 9 x 10 IBULB 0 TO 90 DUTY CYCLE FOR THE PWM SIGNAL CORRESPONDS TO 0 TO 6mA CH 22uF D1 100uH 1 5818 R4 38 3k Y V PWM 1 OV TO 5V 12 NEGCON
36. pply Current Increase During LCD law 0 5A 20 30 mA A Alsw2 LCD Switch On Time Switch Minimum On Time Measured at CCFL Vsw and LCD Vsw 0 45 us The denotes specifications which apply over the specified operating Note 2 Does not include switch leakage temperature range Note 3 For duty cycles DC between 50 and 75 minimum Note 1 T is calculated from the ambient temperature Ta and power guaranteed switch current is given by 1 4 1 393 DC for the CCFL dissipation Pp according to the following formula regulator and I jy 0 7 1 393 DC for the LCD contrast regulator due to LT1182CS LT1183CS LT1184CS LT1184FCS T Ta Pp x 100 C W internal slope compensation circuitry LY Ue LT1182 LT1183 LT1 184 LT1 1845 TYPICAL PERFORMANCE CHARACTERISTICS LT1182 LT1183 Supply Current LT1184 LT1184F Supply Current Shutdown Current vs Temperature vs Temperature vs Temperature 14 10 100 13 9 90 12 8 80 s Vin 30V 1l
37. provides stable loop compensation and an averaging function to the error sink current Therefore input programming current is related to average Royer converter current Floating lamp circuits operate similarly to grounded lamp circuits except for the derivation of the feedback signal The transfer function between primary side converter current and input programming current must be empiri cally determined and is dependent upon a myriad of factors including lamp characteristics display construc tion transformer turns ratio and the tuning of the Royer oscillator Once again lamp current will be slightly higher at one end of the lamp and input programming current should be set for this higher level to insure that the lamp is not overdriven The internal 0 1Q high side sense resistor on the LT1182 LT1183 LT1184F is rated fora maximum DC current of 1A However this resistor can be damaged by extremely high surge currents at start up The Royer converter typically uses afew microfarads of bypass capacitance at the center tap ofthetransformer This capacitor charges up when the system is first powered by the battery pack or an AC wall adapter Theamountof current delivered at start up can be LY 17 11182 1171183 111184 111184 APPLICATIONS INFORMATION very large if the total impedance in this path is small and the voltage source has high current capability Linear Technology recommends the use of an aluminum electr
38. r LCD Contrast Control LT1173 24kHZ 1A Micropower DC DC Converter for LCD Contrast Control Hysteretic LT1186 200kHz 1 25A CCFL Switching Regulator with DAC for Bits to Brightness Control LT1372 500kHz 1 5A Current Mode Switching Regulator for CCFL or LCD Contrast Control PACKAGE DESCRIPTION Dimensions in inches millimeters unless otherwise noted S Package 16 Lead Plastic SOIC 0 386 0 394 B 8 804 10 008 aet ao 45 gt lt 0 053 0 069 0 004 0 010 16 15 14 13 12 11 10 9 0 508 1 346 1 752 0 101 0 254 0 008 0 010 iue a E 4 0228 0244 0 150 0 157 anid 0 019 o 5791 6197 8 810 3 988 _ 0016 0050 m 420 0406 _ 1 270 0 355 0 483 1 270 TYP THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0 006 INCH 0 15mm Linear Technology Corporation aa USA 1630 McCarthy Blvd Milpitas CA 95035 7487 TECHNOLOGY 408 432 1900 FAX 408 434 0507 TELEX 499 3977 LINEAR TECHNOLOGY CORPORATION 1995
39. rnal 1 24V reference and the Summing voltage in the LT1182 LT1183 LT1184 LT1184F It is also a sense terminal for the LCD dual input error amplifier in the LT1182 LT1183 Connect external feedback divider networks that terminate to ground and frequency compensation components that terminate to ground directly to this pin for best regulation and performance SHUTDOWN Pin 6 Pulling this pin low causes complete regulator shutdown with quiescent current typically re duced to 35uA The nominal threshold voltage for this pin is 0 85V If the pin is not used it can float high or be pulled to a logic high level maximum of 6V Carefully evaluate active operation when allowing the pin to float high Capacitive coupling into the pin from switching transients could cause erratic operation CCFL Pin 16 This pin is the collector of the internal NPN power switch for the CCFL regulator The power switch provides a minimum of 1 25A Maximum switch current is a function of duty cycle as internal slope com pensation ensures stability with duty cycles greater than 50 Using a driver loop to automatically adapt base drive current to the minimum required to keep the switch in a quasi saturation state yields fast switching times and high efficiency operation The ratio of switch current to driver current is about 50 1 10 LY PIN FUNCTIONS Bulb Pin 15 This pin connects to the low side of a 7V threshold comparator b
40. rol circuitry are the result of LCD display enclosure sizes remaining fairly constant while display screen sizes have increased Space requirements for connector hardware include the input power supply and control signal connector the lamp connector and the contrast output voltage connector Even though size requirements are shrinking the high voltage AC required to drive the lamp has not decreased In some cases the use of longer bulbs for color portable equipment has increased the high voltage requirement Accommodating the high voltage on the circuit board dictates certain layout spacings and routings involves providing creepages and clearances in the transformer design and most importantly involves routing a hole underneath the CCFL transformer Routing this hole mini mizes high voltage leakage paths and prevents moisture buildup that can result in destructive arcing In addition to high voltage layout techniques use appropriate layout techniques for isolating high current paths from low current signal paths This leaves the remaining space for control circuitry at a premium Minimum component count is required and minimum size for the components used is required This squeeze on component size is often in direct conflict with the goals of maximizing battery life and efficiency Com promise is often the only remaining choice LCD Contrast Circuits The LCD contrast switching regulator on the LT1182 LT1183 operates in many st
41. sinusoidal drive to the lamp Maximizing optical efficiency equates to larger values for the Royer primary side resonating capacitor and smaller values for the Royer secondary side ballast capaci tor The preferred operating point for the CCFL converter is Somewhere in between the best electrical efficiency and the best optical efficiency This operating point maximizes photometric output per watt of input power Making accurate and repeatable measurements of electri cal and optical efficiency is difficult under the best circum stances Requirements include high voltage measure ments and equipment specified for this operation special ized calibrated voltage and current probes wideband RMS voltmeters a photometer and a calorimeter for the backlight enthusiast Linear Technology s Application Note 55 and Design Note 101 contain detailed information regarding equipment needs Input Supply Voltage Operating Range The backlight LCD contrast control circuits must operate over a wide range of input supply voltage and provide excellent line regulation for the lamp current and the contrast output voltage This range includes the normal range of the battery pack itself as well as the AC wall adapter voltage which is normally much higher than the maximum battery voltage A typical input supply is 7V to 28V a 4 to 1 supply range Operation of the CCFL control circuitry from the AC wall adapter generates the worst case stress for the CCF
42. source current provided by the lamp current programmer circuit A single capacitor on the CCFL Vc pin provides both stable loop compensation and an averaging function to the half wave rectified sinusoidal lamp current Therefore input programming current relates to one half of average lamp current This scheme reduces the number of loop com pensation components and permits faster loop transient response in comparison to previously published circuits If a floating lamp configuration is used ground the DIO pin CCFL Ve Pin 4 This pin is the output of the lamp current programmer circuit and the input of the current compara tor for the CCFL regulator Its uses include frequency compensation lamp current averaging for grounded lamp circuits and current limiting The voltage on the CCFL Vc pin determines the current trip level for switch turnoff During normal operation this pin sits at a voltage between 0 95V zero switch current and 2 0V maximum switch current with respect to analog ground AGND This pin has a high impedance output and permits external voltage clamping to adjust current limit A single capacitor to ground provides stable loop compensation This simpli fied loop compensation method permits the CCFL regula tor to exhibit single pole transient response behavior and virtually eliminates transformer output overshoot AGND Pin 5 This pin is the low current analog ground It is the negative sense terminal for the inte
43. t and input programming current must be empirically determined and is dependent on the particular lamp display housing com bination used The lamp and display housing are a distrib uted loss structure due to parasitic lamp to frame capaci tance This means that the current flowing at the high voltage side of the lamp is higher than what is flowing at the DIO pin side of the lamp The input programming current is set to control lamp current at the high voltage side of the lamp even though the feedback signal is the lamp current at the bottom of the lamp This insures that the lamp is not overdriven which can degrade the lamp s Operating lifetime Floating Lamp Configuration In a floating lamp configuration the lamp is fully floating with no galvanic connection to ground This allows the transformer to provide symmetric differential drive to the lamp Balanced drive eliminates the field imbalance asso ciated with parasitic lamp to frame capacitance and re duces thermometering uneven lamp intensity along the lamp length at low lamp currents Carefully evaluate display designs in relation to the physi cal layout of the lamp it leads and the construction of the display housing Parasitic capacitance from any high voltage point to DC or AC ground creates paths for unwanted current flow This parasitic current flow de grades electrical efficiency and losses up to 25 have been observed in practice As an example at a Royer operatin
44. tched mode current source for a current driven Royer class converter with efficiencies as high as 9096 The control loop forces the regulator to pulse width modulate the inductor s average current to maintain constant cur rent in the lamp The constant current s value and thus lamp intensity is programmable This drive technique provides a wide range of intensity control A unique lamp current programming block permits either grounded lamp or floating lamp configurations Grounded lamp cir cuits directly control one half of actual lamp current Floating lamp circuits directly control the Royer s primary side converter current Floating lamp circuits provide differential drive to the lamp and reduce the loss from stray lamp to frame capacitance extending illumination range The LCD contrast switching regulator in the LT1182 LT1183 is typically configured as a flyback converter and generates a bias supply for contrast control Other topol ogy choices for generating the bias supply include a boost converter ora boost charge pump converter The supply s variable output permits adjustment of contrast for the LT1182 LT1183 LT1 184 LT1 1 84F majority of available displays Some newer types of dis plays require a fairly constant supply voltage and provide contrast adjustmentthrough a digital control pin A unique dual polarity error amplifier and the selection of a flyback converter topology allow either positive or negative LCD contrast vo
45. witching frequency minimizes the size of required mag netic components The use of current mode switching techniques with cycle by cycle limiting gives high reliabil ity and simple loop frequency compensation The LT1182 LT1183 LT1184 LT1184F are all available in 16 pin nar row SO packages ABSOLUTE MAXIMUM RATINGS Vin Royer Bulb Cua t tote atn 30V CCFL Ve EOD 60V dr a OW mamata UNUM 6V leer Input Current 10mA DIO Input Current Peak lt 100ms 100mA LT1182 FBP 171183 FB Pin Current 2mA LT1183 LT1184 1184F REF Pin Source Current 1mA Junction Temperature Note 1 100 C Operating Ambient Temperature Range 0 C to 100 C Storage Temperature Range 6596 to 150 C Lead Temperature Soldering 10 sec 300 C PACKAGE ORDER INFORMATION ORDER PART ndis ORDER PART CCFL PGND CCFL Vsw NUMBER CCFL PGND CCFL Vsw NUMBER lccrL BULB BULB DIO BAT DIO BAT CCFL Vc ROYER 11118205 CCFL Vc ROYER LT1183CS AGND Vin AGND Vin SHUTDOWN FBP SHUTDOWN REF LCD Vc FBN LCD Vc FB LCD PGND LCD Vow LCD PGND 8 LCD Vsw S PACKAGE S PACKAGE 16 LEAD PLASTIC SO 16 LEAD PLASTIC SO 100 C 100 C W Timax 100 C 64 100 C W SEMEN ORDER PART I ORDER PART CCFL PGND CCFL Vsw NUMBER CCFL PGND
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LINEAR TECHNOLOGY LT1182/LT1183/LT1184/LT1184F Manual