LTC1697 High Efficiency Low Power 1W CCFL Switching Regulator U FEATURES DESCRIPTIO ■ Operates from Single Li-Ion Battery 2.8V to 5.5V Input Voltage Range Very Low Shutdown Current: <2µA Synchronous Buck Architecture for High Efficiency PWM Dimming Frequency Adjustable with a Single Capacitor Accurate Lamp Current Maximizes Lamp Lifetime Fixed Frequency Operation at 300kHz Internal or External PWM Dimming Small 10-Pin MSOP Package The LTC®1697 is designed to control a single 1W cold cathode fluorescent lamp (CCFL). An internal PWM dimming system maximizes efficiency and dimming range. Accurate lamp currents can be set with a single external resistor. PDAs Handheld Computers Portable Instruments Handheld GPS with Map Display Handheld TV/Video Monitor The LTC1697 is available in the MSOP-10 package. ■ ■ ■ ■ ■ ■ ■ ■ The LTC1697 includes a synchronous current mode PWM controller with internal 1A MOSFET switches. It contains a 300kHz oscillator, 0.8V reference, and internal current sense. It operates from a 2.8V to 5.5V input voltage. The LTC1697 also has a thermal limit and a shutdown that reduces supply current to <2µA. U APPLICATIO S ■ ■ ■ ■ , LTC and LT are registered trademarks of Linear Technology Corporation. Protected by U.S. Patent 6522116. U ■ TYPICAL APPLICATIO 6 1 VIN 2.8V TO 5.5V 10 330Ω 5 2 3 27pF 1kV 4 ICCFL vs RPROG 10 9 8 0.15µF CCFL LAMP 7 200k 33µH Li-Ion CELL + ICCFL (mA) 6 VIN SW 0VSEN OFF ON DIMMING INPUT 1V(0%) – 2V(100%) SHDN LTC1697 VDIM LAMP 5 4 3 CDIM 10µF 0.022µF RPROG GND 8.25k 2 4k VC 0.1µF 6k 8k 10k RPROG (Ω) 20k 1967 TA01b 1697 TA01 1697f 1 LTC1697 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Notes 1, 2) VIN Voltage .................................................. –0.5V to 6V VC, OVSEN, CDIM, RPROG, SW Voltages ................................... –0.5V to (VIN + 0.3V) SHDN, VDIM Pins ......................................... –0.5V to 6V LAMP Pin ................................................. –0.5V to 0.5V Operating Temperature Range (Note 5) ...–40°C to 85°C Storage Temperature Range ..................–65°C to 125°C Lead Temperature (Soldering, 10 sec).................. 300°C ORDER PART NUMBER TOP VIEW 1 2 3 4 5 CDIM VDIM 0VSEN SW GND 10 9 8 7 6 SHDN RPROG VC VIN LAMP LTC1697EMS MS PART MARKING MS PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 125°C, θJA = 160°C/W 1 LAYER BOARD LTZR Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. 2.8V < VIN ≤ 5.5V unless otherwise specified. SYMBOL PARAMETER CONDITIONS VIN Operating Supply Voltage Range (Note 2) VUVLO Undervoltage Lockout IQ-SHDN Quiescent Current - SHDN SHDN = 0V; VDIM = 0V IQ-Active Quiescent Current - Active VC = 0V, SHDN = VIN = VDIM = 4.2V (Note 4) ILEAK Switch Leakage RON Switch On Resistance MIN ● TYP 2.8 5.5 V V 1 2 µA 0.9 1.5 mA 0.1 1 µA 0.18 IMAX Switch Current Limit ● 0.9 % DC Duty Cycle ● 0 fSWITCH Switching Frequency ● 240 fDIM Dimming PWM Frequency CDIM = 0.022µF (Note 3) ● 190 VDIM VDIM Input Voltage Dimming PWM Duty Cycle = 0% Dimming PWM Duty Cycle = 100% IDIM VDIM Input Bias Current VDIM = 2V RLAMP Internal RLAMP Resistance LAMP Pin to GND IL(ERROR) Lamp Current Accuracy |1– ILAMP(AVG)/(32/6.4k)| • 100% (Note 6) ILAMP = 5mA ● RP(RANGE) Programming Resistor Range (Note 10) ● VSHDN-H SHDN Input High VSHDN-L SHDN Input Low (Note 9) ISHDN SHDN Input Current VSHDN = VIN ● IOVSEN Overvoltage Sense Protect Current (Note 7) ILAMP = 5mA, RPROG = 6.4k ● VOVSEN Overvoltage Sense Pin Voltage ● VDIM(SD-I) Passive Shutdown Voltage (Note 8) ● VDIM(SD-H) Not in Passive Shutdown ● UNITS 2.77 ● VIN = 4V MAX Ω 1.6 A 95 % 300 370 kHz 250 310 Hz 1.0 2.0 V V ±1 µA 50 60 Ω 2 6 % 16 kΩ 6.4 1.2 V 0.4 V 0.1 1 µA 16.65 21.5 26.35 µA 0.95 1.2 1.05 1.5 V 0.4 V V 1697f LTC1697 ELECTRICAL CHARACTERISTICS Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: All voltages specified with respect to GND pin. Note 3: The dimming PWM frequency is set by the equation 5Hz/CDIM(µF). Note 4: Actual operating current will be higher due to lamp operating current. Note 5: The LTC1697 is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 6: ILAMP(AVG) = the average of the magnitude (absolute value) of the positive and negative lamp current flowing into and out of the LAMP pin. Note 7: For currents at or above IOVSEN(ON), the switch duty cycle will be 0%. Note 8: At VDIM voltages below VDIM(SHDNON) the LTC1697 behaves as if the SHDN pin was pulled low. Note 9: To minimize IQ shutdown, pull the SHDN pin below 0.1V. Note 10: 2mA ≤ ILAMP ≤ 5mA. U U U PI FU CTIO S CDIM (Pin 1): Dimming Capacitor. Connect the pin to GND with a 0.022µF capacitor (nominal). The value of capacitance on the CDIM pin determines the dimming PWM frequency. The transfer function of capacitance to frequency is 5Hz/CDIM(µF). GND (Pin 5): Signal and Power Ground for the LTC1697. VDIM (Pin 2): Dimming Control Pin. The VDIM pin controls the duty cycle of the dimming PWM. It ranges from 0% at VDIM = 1V to 100% at VDIM = 2V. If the VDIM voltage is <0.4V the LTC1697 will enter shutdown mode after ≈50ms. VC (PIN 8): Compensation Node. Connect this pin to GND through a 0.1µF capacitor. See Application Information section. A frequency compensation network is connected to this pin to compensate the loop. See the section “VC Compensation” for guidelines. 0VSEN (Pin 3): Overvoltage Sense Pin. Protects the highvoltage transformer from the overvoltage condition that occurs when the lamp is open or not present. This pin is connected through a resistor to the emitters of the drive transistors of the Royer oscillator. SW (Pin 4): Switch Pin. Connect the inductor and optional Schottky diode here. Minimize trace length to keep EMI and high frequency ringing down. LAMP (Pin 6): Lamp Current Feedback Pin. Connect this pin to the CCFL lamp. VIN (Pin 7): Input Supply Pin. RPROG (Pin 9): Lamp Current Programming. Connect this pin to GND with a 6.4k 1% resistor (nominal). See Application Information section for resistor selection. SHDN (Pin 10): Shutdown. Grounding this pin shuts down the LTC1697. Tie to >1V to enable. 1697f 3 LTC1697 W BLOCK DIAGRA TO ROYER OSCILLATOR 200k SW 4 VIN 7 2.8V TO 5.5V ANTI SHOOTTHRU PROTECTION SHDN 10 ISENSE AMP N SHUTDOWN 3 0VSEN + CURRENT LIMIT TRANSFORMER VOLTAGE PROTECTION 1.6A TYP – – 8 CURRENT COMP PWM LOGIC + 0.8V + – Σ – + PWM OSC SLOPE COMP GND VC 9 – 5 2V 1V DIMMING OSC 0.7V 1 + RP ILAMP + LAMP FB 6 LAMP RPROG 50Ω – 2 CDIM RPROG 1697 BD VDIM 1697f LTC1697 U W U U APPLICATIO S I FOR ATIO Background Operation Current generation handheld computers and instruments typically use backlit liquid crystal displays (LCDs). Cold cathode fluorescent lamps (CCFLs) provide the highest available efficiency for backlighting the display, where providing the most light 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 ideally 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, which can interfere with other devices and degrade overall operating efficiency. Sinusoidal CCFL drive also maximizes current-to-light conversion in the lamp. The circuit also permits lamp intensity control from zero to full brightness with no hysteresis or “pop-on.” The LTC1697 is a fixed frequency, current mode regulator. Such a switcher controls switch duty cycle directly by switch current rather than by output voltage. Referring to the block diagram for the LTC1697, the NMOS switch turns ON at the start of each oscillator cycle. The NMOS switch turns back OFF when switch current reaches a predetermined level. The small size and battery-powered operation associated with LCD-equipped apparatus dictate low component count and high efficiency for these circuits. Size constraints place severe limitations on circuit architecture and long battery life is usually a priority. Handheld portable computers offer an excellent example. The CCFL and its power supply can be responsible for almost 50% of the total battery drain. The CCFL regulator drives an inductor that acts as a switch-mode current source for a current-driven Royerclass converter with efficiencies as high as 90%. The control loop forces the CCFL PWM to modulate the average inductor current to maintain constant current in the lamp. This constant current and the resulting lamp intensity is programmable. Lamp intensity is further controlled by modulating the current to the Royer converter at 150Hz to 500Hz. Current Sensing Lossless current sensing converts the peak current signal to a voltage which is summed with the internal slope compensation. This summed signal is compared to VC to provide a peak current control command for the PWM. Current Limit The current limit amplifier will shut the NMOS switch off once the current exceeds the current limit threshold. The current amplifier delay to the output is typically 50ns. Synchronous Rectifier The LTC1697 operates as a synchronous converter. When the NMOS switch turns OFF as mentioned above, the PMOS switch turns ON. This gives a low resistance current path for the inductor current back to VIN. Dimming PWM An on-chip PWM dimming circuit enables and disables the current mode regulator for each dimming cycle. It also disconnects the feedback network from the compensation node (VC) to reduce slew time at the next enable time. The oscillator for the dimming PWM produces a triangle wave whose frequency is determined by an external capacitor on the CDIM pin. The dimming PWM frequency is equal to 5Hz/CDIM(µF) with its duty cycle set by the voltage on the 1697f 5 LTC1697 U W U U APPLICATIO S I FOR ATIO VDIM pin where DC = 0% at VDIM = 1V and DC = 100% at VDIM = 2V. If desired, the internal dimming PWM can be overridden by grounding the CDIM pin and applying the input PWM signal to the VDIM pin. This external PWM signal should be in the range of 150Hz to 500Hz. line regulation becomes unacceptable. A typical value for the VC capacitor is 0.1µF. For further information on compensation please refer to Application Note 65 or consult the factory. OVSEN Operation Lamp Feedback In a typical application, the LAMP pin is connected to the low voltage side of the lamp. The lamp pin is internally connected to ground by a ~50Ω resistor. This resistor will limit the voltage on the LAMP pin to ±0.35V for a 5mARMS lamp current. The lamp feedback circuit removes a current from VC approximating 1/40 of the absolute value of the current through the 50Ω resistor. The OVSEN pin can be used to protect the high voltage transformer from an overvoltage condition that can occur when the lamp is open or not present. Connect this pin through a resistor to the emitters of the drive transistors of the Royer oscillator. The voltage at the OVSEN pin is specified by VOVSEN. The duty cycle of the LTC1697 SW pin will be 0% when the current flowing out of the OVSEN pin reaches IOVSEN (protect). See the manufacturers transformer specifications for transformer voltage ratings. Current Programming Input (RPROG) The ILAMP current is set with an external resistor connected between this pin and ground. ILAMP = 32V/RPROG. VC Compensation The VC node is the point where the lamp feedback current, the programming current, and the control for the switching controller meet. A single capacitor must be connected from the VC pin to ground to compensate the feedback loop. Careful consideration should be given to the value of capacitance used. A large value (1µF) will give excellent stability at high lamp currents but will result in degraded line regulation. On the other hand, a small value (10nF) will result in overshoot and poor load regulation. The value chosen will depend on the maximum load current and dimming range. After these parameters are decided upon, the value of the VC capacitor should be increased until the Thermal Shutdown This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. Shutdown Operation There are two ways to place the LTC1697 in shutdown. The SHDN pin can be pulled below VSHDN-1, or the VDIM pin can be pulled below VDIM(SD-I) for more than approximately 50mS. For normal operation, both pins must be pulled high. The SHDN pin must be pulled above VSHDN-H, and the VDIM pin must be pulled above VDIM (SD-H). 1697f LTC1697 U PACKAGE DESCRIPTIO MS Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1661) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.50 0.305 ± 0.038 (.0197) (.0120 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 10 9 8 7 6 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) DETAIL “A” 0.497 ± 0.076 (.0196 ± .003) REF 0° – 6° TYP GAUGE PLANE 1 2 3 4 5 0.53 ± 0.152 (.021 ± .006) DETAIL “A” 0.86 (.034) REF 1.10 (.043) MAX 0.18 (.007) SEATING PLANE 0.17 – 0.27 (.007 – .011) TYP 0.50 (.0197) BSC 0.127 ± 0.076 (.005 ± .003) MSOP (MS) 0603 NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 1697f 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 7 LTC1697 U TYPICAL APPLICATIO External PWM Dimming 6 5 T1 1 10 2 R1 330Ω VIN 2.8V TO 5.5V 3 4 C2 Q1 0.15µF Q2 L1 33µH Li-Ion CELL + C3 27pF 1kV CCFL LAMP 200k VIN SW 0VSEN OFF ON SHDN LTC1697 VDIM LAMP 1V TO 2V 0V 150Hz TO 500Hz C1 10µF C1: TAIYO YUDEN JMK212BJ106MM C2: PANASONIC ECH-U1H154JC9 L1:SUMIDA CDRH6D28-330NC CDIM RPROG GND VC 8.25k C4 0.1µF 1697 TA02 Q1, Q2: ZETEX FMMT-617 R1: 330Ω,1206 PKG T1: SUMIDA CLQ122-S-227-5316 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1170/LT1170HV 5A, 100kHz High Efficiency Switching Regulator VIN: 3V to 40V/60V, VOUT(MAX) = 65V/75V, IQ = 6mA, ISD = <50µA, N8, S16, TO220-5, DD Packages LT1182/LT1183 CCFL/LCD Contrast Switching Regulators, CCFL Switch: 1.25A, LCD Switch: 625mA VIN: 3V to 30V, VOUT(MAX) = 60V, IQ = 6mA, ISD = 35µA, SO-16 Package LT1184/LT1184F 1.25A, 200kHz, CCFL Current Mode Switching Regulator VIN: 3V to 30V, VOUT(MAX) = 60V, IQ = 6mA, ISD = 35µA, SO-16 Package LT1186/LT1186F 1.25A, 100kHz, DAC Programmable CCFL Current Mode Switching Regulator VIN: 4.5V to 30V, VOUT(MAX) = 60V, IQ = 6mA, ISD = 35µA SO-16 Package LT1372/LT1372HV/ LT1377 1.5A, 500kHz/1MHz, High Efficiency Switching Regulator VIN: 2.7V to 30V, VOUT(MAX) = 35V, IQ = 4mA, ISD = <12µA N8, S8 Packages LT1373/LT1373HV 1.5A, 250kHz High Efficiency Switching Regulator can Regulate Positive or Negative Outputs VIN: 0.5V to 5V, VOUT(MAX) = 35V, IQ = 1mA, ISD = <12µA N8, S8 Packages LT1768 High Power CCFL Controller for Wide Dimming Range and Maximum Lamp Lifetime VIN: 8V to 24V, VOUT(MAX) = 28V, IQ = 7mA, ISD = 65µA SSOP-16 Package LT1786F 1.25A, 200kHz, SMBus Controlled CCFL Switching Regulator Precision 100mA Full Scale Current VIN: 4.5V to 30V, VOUT(MAX) = 60V, IQ = 6mA, ISD = 150µA SO-16 Package 1697f Linear Technology Corporation LT/TP 1004 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2004