LT3483 Inverting Micropower DC/DC Converter with Schottky DESCRIPTION FEATURES n n n n n n n n n n Internal 40V Schottky Diode One Resistor Feedback (Other Resistor Inside) Internal 40V, 200mA Power Switch Generates Regulated Negative Outputs to –38V Low Quiescent Current: 40μA in Active Mode <1μA in Shutdown Mode Low VCESAT Switch: 200mV at 150mA Wide Input Range: 2.5V to 16V Uses Small Surface Mount Components Output Short-Circuit Protected Available in a 6-Lead SOT-23 and Low Profile 8-Lead DFN (2mm × 2mm × 0.75mm) Packages APPLICATIONS n n n n n LCD Bias Handheld Computers Battery Backup Digital Cameras OLED Bias The LT®3483 is a micropower inverting DC/DC converter with integrated Schottky and one resistor feedback. The small package size, high level of integration and use of tiny surface mount components yield a solution size as small as 40mm2. The device features a quiescent current of only 40μA at no load, which further reduces to 0.1μA in shutdown. A current limited, fixed off-time control scheme conserves operating current, resulting in high efficiency over a broad range of load current. A precisely trimmed 10μA feedback current enables one resistor feedback and virtually eliminates feedback loading of the output. The 40V switch enables voltage outputs up to –38V to be generated without the use of costly transformers. The LT3483’s low 300ns off-time permits the use of tiny low profile inductors and capacitors to minimize footprint and cost in space-conscious portable applications. The LT3483 is available in the low profile (1mm) SOT-23 (ThinSOT™) and 8-lead DFN (2mm × 2mm × 0.75mm) packages. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Patent Pending TYPICAL APPLICATION 3.6V to –8V DC/DC Converter VIN 3.6V Efficiency and Power Loss 75 0.22μF 10μH 10Ω 4.7μF D LT3483 SHDN FB GND 5pF 806k VOUT –8V 25mA 2.2μF EFFICIENCY (%) VIN EFFICIENCY 70 100 65 10 POWER LOSS 60 POWER LOSS (mW) SW 1000 VIN = 3.6V 1 3483 TA01a 55 0.1 1 10 LOAD CURRENT (mA) 0.1 100 3483 TA01b 3483fb 1 LT3483 ABSOLUTE MAXIMUM RATINGS (Note 1) VIN Voltage ............................................................... 16V SW Voltage .............................................................. 40V D Voltage ............................................................... –40V FB Voltage ............................................................... 2.5V SHDN Voltage .......................................................... 16V Operating Ambient Temperature Range (Note 2) LT3483E ...............................................– 40°C to 85°C LT3483I ..............................................– 40°C to 125°C Junction Temperature ......................................... 125°C Storage Temperature Range.................. –65°C to 150°C Lead Temperature (Soldering, 10 sec) (TSOT-23 Package Only) .................................. 300°C PIN CONFIGURATION TOP VIEW TOP VIEW 8 SHDN FB 1 GND 2 9 SW 1 7 D GND 3 6 NC SW 4 5 VIN GND 2 FB 3 6 VIN 5D 4 SHDN S6 PACKAGE 6-LEAD PLASTIC TSOT-23 TJMAX = 125°C, θJA = 256°C/W IN FREE AIR θJA = 120°C/W ON BOARD OVER GROUND PLANE DC PACKAGE 8-LEAD (2mm × 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 121°C/W EXPOSED PAD (PIN 9) IS GND ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT3483EDC#PBF LT3483EDC#TRPBF LCYT 8-Lead (2mm × 2mm) Plastic DFN –40°C to 85°C LT3483ES6#PBF LT3483ES6#TRPBF LTBKX 6-Lead Plastic TSOT-23 –40°C to 85°C LT3483IDC#PBF LT3483IDC#TRPBF LCYT 8-Lead (2mm × 2mm) Plastic DFN –40°C to 125°C LT3483IS6#PBF LT3483IS6#TRPBF LTBKX 6-Lead Plastic TSOT-23 –40°C to 125°C LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT3483EDC LT3483EDC#TR LCYT 8-Lead (2mm × 2mm) Plastic DFN –40°C to 85°C LT3483ES6 LT3483ES6#TR LTBKX 6-Lead Plastic TSOT-23 –40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 3483fb 2 LT3483 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, VSHDN = 3.6V unless otherwise specified. PARAMETER CONDITIONS MIN VIN Operating Range TYP 2.5 VIN Undervoltage Lockout MAX UNITS 16 V 2 2.4 V FB Comparator Trip Voltage to GND (VFB) FB Falling ● 0 5 12 mV FB Output Current (Note 3) FB = VFB – 5mV ● –10.2 –10 –9.7 μA FB Comparator Hysteresis FB Rising Quiescent Current in Shutdown VSHDN = GND Quiescent Current (Not Switching) FB = –0.05V IFB Line Regulation 2.5V ≤ VIN ≤ 16V 10 40 Switch Off-Time mV 1 μA 50 μA 0.07 %/V 300 Switch Current Limit 170 Switch VCESAT ISW = 150mA to GND Switch Leakage Current SW = 40V Rectifier Leakage Current D = – 40V Rectifier Forward Drop ID = 150mA to GND 200 SHDN Pin Current Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. 230 200 mA mV 1 μA 4 μA 0.64 SHDN Input Low Voltage SHDN Input High Voltage ns V 0.4 V 10 μA 1.5 V 6 Note 2: The LT3483E is guaranteed to meet specifications from 0°C to 85°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. The LT3483I is guaranteed to meet specifications over the –40°C to 125°C operating temperature range. Note 3: Current flows out of the pin. 3483fb 3 LT3483 TYPICAL PERFORMANCE CHARACTERISTICS VFB Current VFB Voltage Switch Off Time 16 10.2 400 350 VFB VOLTAGE (mV) VFB CURRENT (μA) 10.0 SWITCH OFF TIME (ns) 12 10.1 8 4 9.9 300 250 200 150 100 50 9.8 –50 –25 50 75 0 25 TEMPERATURE (°C) 100 0 –50 125 –25 50 75 0 25 TEMPERATURE (°C) Switch Current Limit 190 180 –25 0 25 50 75 TEMPERATURE (°C) 100 125 3483 G04 10 SHDN PIN BIAS CURRENT (μA) QUIESCENT CURRENT (μA) 220 200 0 25 75 50 TEMPERATURE (°C) 40 30 20 10 0 –50 –25 50 75 0 25 TEMPERATURE (°C) 100 125 SHDN Pin Bias Current Quiescent Current 210 –25 3483 G03 50 230 SWITCH CURRENT LIMIT (mA) 0 –50 125 3483 G02 3483 G01 170 –50 100 100 125 3483 G05 TA = 25°C 8 6 4 2 0 0 8 4 12 SHDN PIN VOLTAGE (V) 16 3483 G06 3483fb 4 LT3483 PIN FUNCTIONS (DFN/TSOT-23) FB (Pin 1/Pin 3): Feedback. Place resistor to negative output here. Set resistor value R1 = VOUT/10μA. D (Pin 7/Pin 5): Anode Terminal of Integrated Schottky Diode. Connect to negative terminal of transfer capacitor and external inductor L2 (flyback configuration) or to cathode of external Schottky diode (inverting charge pump configuration). GND (Pins 2, 3/Pin 2): Ground. For DFN package, tie both pin 2 and pin 3 together to ground. SW (Pin 4/Pin 1): Switch. Connect to external inductor L1 and positive terminal of transfer capacitor. SHDN (Pin 8/Pin 4): Shutdown. Connect to GND to turn device off. Connect to supply to turn device on. VIN (Pin 5/Pin 6): Input Supply. Must be locally bypassed with 1μF or greater. Exposed Pad (Pin 9/NA): GND. The exposed pad should be soldered to the PCB ground to achieve the rated thermal performance. NC (Pin 6/NA): No Connection. BLOCK DIAGRAM L1A VIN 6 R1 3 FB COUT 5 SW D 300ns DELAY 125k VOUT VOUT • CFLY 1 VIN 1.250V REFERENCE L1B • S Q R Q Q1 + D1 25mV + A3 A2 – + – A1 0.1Ω – 0.1Ω 20mV GND 2 OPTIONAL CHARGE PUMP CONFIGURATION. L1B REPLACED WITH: D2 D 3483 BD PIN NUMBERS CORRESPOND TO THE 6-PIN TSOT-23 PACKAGE R2 VOUT 3483fb 5 LT3483 OPERATION The LT3483 uses a constant off-time control scheme to provide high efficiency over a wide range of output currents. Operation can be best understood by referring to the Block Diagram. When the voltage at the FB pin is approximately 0V, comparator A3 disables most of the internal circuitry. Output current is then provided by external capacitor COUT, which slowly discharges until the voltage at the FB pin goes above the hysteresis point of A3. Typical hysteresis at the FB pin is 10mV. A3 then enables the internal circuitry, turns on power switch Q1, and the currents in external inductors L1A and L1B begin to ramp up. Once the switch current reaches 200mA, comparator A1 resets the latch, which turns off Q1 after about 80ns. Inductor current flows through the internal Schottky D1 to GND, charging the flying capacitor. Once the 300ns off-time has elapsed, and internal diode current drops below 250mA (as detected by comparator A2), Q1 turns on again and ramps up to 200mA. This switching action continues until the output capacitor charge is replenished (until the FB pin decreases to 0V), then A3 turns off the internal circuitry and the cycle repeats. The inverting charge pump topology replaces L1B with the series combination D2 and R2. APPLICATIONS INFORMATION CHOOSING A REGULATOR TOPOLOGY Inverting Charge Pump The inverting charge pump regulator combines an inductor-based step-up with an inverting charge pump. This configuration usually provides the best size, efficiency and output ripple and is applicable where the magnitude of VOUT is greater than VIN. Negative outputs to –38V can be produced with the LT3483 in this configuration. For cases where the magnitude of VOUT is less than or equal to VIN, use a 2-inductor or transformer configuration such as the inverting flyback. In the inverting charge pump configuration, a resistor is added in series with the Schottky diode between the negative output and the D pin of the LT3483. The purpose of this resistor is to smooth/reduce the current spike in the flying capacitor when the switch turns on. A 10Ω resistor works well for a Li+ to –8V application, and the impact to converter efficiency is less than 3%. The resistor values recommended in the applications circuits also limit the switch current during a short-circuit condition at the output. Inverting Flyback The inverting flyback regulator, shown in the –5V application circuit, uses a coupled inductor and is an excellent choice where the magnitude of the output is less than or equal to the supply voltage. The inverting flyback also performs well in a step-up/invert application, but it occupies more board space compared with the inverting charge pump. Also, the maximum |VOUT| using the flyback is less than can be obtained with the charge pump—it is reduced from 38V by the magnitudes of VIN and ringing at the switch node. Under a short-circuit condition at the output, a proprietary technique limits the switch current and prevents damage to the LT3483 even with supply voltage as high as 16V. As an option, a 0.47μF capacitor may be added between terminals D and SW of LT3483 to suppress ringing at SW. Inductor Selection Several recommended inductors that work well with the LT3483 are listed in Table 1, although there are many other manufacturers and devices that can be used. Consult each manufacturer for more detailed information and for their entire selection of related parts. Many different sizes and shapes are available. For inverting charge pump regulators with input and output voltages below 7V, a 4.7μH or 6.8μH inductor is usually the best choice. For flyback regulators or for inverting charge pump regulators where the input or output voltage is greater than 7V, a 10μH inductor is usually the best choice. A larger value inductor can be used to slightly increase the available output current, but limit 3483fb 6 LT3483 APPLICATIONS INFORMATION it to around twice the value recommended, as too large of an inductance will increase the output voltage ripple without providing much additional output current. to 4.7μF. The following formula is useful to estimate the output capacitor value needed: COUT = Table 1. Recommended Inductors PART MAX L IDC DCR HEIGHT (μH) (mA) (Ω) (mm) MANUFACTURER LQH2MCN4R7M02L LQH2MCN6R8M02L LQH2MCN100M02L 4.7 6.8 10 300 255 225 0.84 1.0 1.2 0.95 Murata www.murata.com SDQ12 Coupled Inductor 10 15 980 780 0.72 1.15 1.2 Cooper Electronics Tech www.cooperet.com 744876 Coupled Inductor 10 550 0.46 1.2 Würth Elektronik www.we-online.com where ISW = 0.25A and ΔVOUT = 30mV. The flying capacitor in the inverting charge pump configuration ranges from 0.1μF to 0.47μF. Multiply the value predicted by the above equation for COUT by 1/10 to determine the value needed for the flying capacitor. Table 2. Recommended Ceramic Capacitor Manufacturers MANUFACTURER URL Capacitor Selection The small size and low ESR of ceramic capacitors make them ideal for LT3483 applications. Use of X5R and X7R types is recommended because they retain their capacitance over wider voltage and temperature ranges than other dielectric types. Always verify the proper voltage rating. Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for more detailed information on their entire selection of ceramic capacitors. A 4.7μF ceramic bypass capacitor on the VIN pin is recommended where the distance to the power supply or battery could be more than a couple inches. Otherwise, a 1μF is adequate. A capacitor in parallel with feedback resistor R1 is recommended to reduce the output voltage ripple. Use a 5pF capacitor for the inverting charge pump, and a 22pF value for the inverting flyback or other dual inductor configurations. Output voltage ripple can be reduced to 20mV in some cases using this capacitor in combination with an appropriately selected output capacitor. The output capacitor is selected based on desired output voltage ripple. For low output voltage ripple in the inverting flyback configuration, use a 4.7μF to 10μF capacitor. The inverting charge pump utilizes values ranging from 0.22μF L •ISW 2 –VOUT • ΔVOUT AVX www.avxcorp.com Kemet www.kemet.com Murata www.murata.com Taiyo Yuden www.tyuden.com Setting the Output Voltage The output voltage is programmed using one feedback resistor according to the following formula: R1= – VOUT 10μA Inrush Current When VIN is increased from ground to operating voltage, an inrush current will flow through the input inductor and integrated Schottky diode to charge the flying capacitor. Conditions that increase inrush current include a larger, more abrupt voltage step at VIN, a larger flying capacitor, and an inductor with a low saturation current. While the internal diode is designed to handle such events, the inrush current should not be allowed to exceed 1.5A. For circuits that use flying capacitors within the recommended range and have input voltages less than 5V, inrush current remains low, posing no hazard to the device. In cases where there are large steps at VIN, inrush current should be measured to ensure operation within the limits of the device. 3483fb 7 LT3483 APPLICATIONS INFORMATION Board Layout Considerations and area of all traces connected to the SW and D pins. In particular, it is desirable to minimize the trace length to and from the flying capacitor, since current in this capacitor switches directions within a cycle. Always use a ground plane under the switching regulator to minimize interplane coupling. As with all switching regulators, careful attention must be given to the PCB board layout and component placement. Proper layout of the high frequency switching path is essential. The voltage signals of the SW and D pins have sharp rising and falling edges. Minimize the length Suggested Layout (DFN) for Inverting Charge Pump VOUT R1 A COUT SHDN 8 1 2 GND K 7 9 3 6 4 5 VIN CIN CFLY L1 3483 AI02 Suggested Layout (SOT-23) for Inverting Charge Pump + GND CIN L1 CFLY VIN 1 6 2 5 3 4 COUT R1 SHDN VOUT 3483 AI01 3483fb 8 LT3483 TYPICAL APPLICATION 3.6V to –8V DC/DC Converter Low Profile, Small Footprint C2 0.22μF L1 10μH VIN 3.6V D1 10Ω SW VIN C1 4.7μF D LT3483 5pF SHDN FB GND R1 806k C1: MURATA GRM219R61A475KE34B C2: TAIYO YUDEN LMK107BJ224 C3: MURATA GRM219R61C225KA88B D1: PHILIPS PMEG2005EB L1: MURATA LQH2MCN100K02L VOUT –8V 25mA C3 2.2μF 3483 TA04a Switching Waveform VOUT 20mV/DIV ISW 100mA/DIV 2μs/DIV 3483 TA04b 3483fb 9 LT3483 PACKAGE DESCRIPTION DC Package 8-Lead Plastic DFN (2mm × 2mm) (Reference LTC DWG # 05-08-1719 Rev Ø) 0.70 ±0.05 2.55 ±0.05 1.15 ±0.05 0.64 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.45 BSC 1.37 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED R = 0.05 TYP 2.00 ±0.10 (4 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) R = 0.115 TYP 5 8 0.40 ± 0.10 0.64 ± 0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.25 × 45° CHAMFER (DC8) DFN 0106 REVØ 4 0.200 REF 1 0.23 ± 0.05 0.45 BSC 0.75 ±0.05 1.37 ±0.10 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 3483fb 10 LT3483 PACKAGE DESCRIPTION S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636 Rev B) 0.62 MAX 2.90 BSC (NOTE 4) 0.95 REF 1.22 REF 3.85 MAX 2.62 REF 1.4 MIN 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 – 0.45 6 PLCS (NOTE 3) 0.95 BSC 0.80 – 0.90 0.20 BSC 0.01 – 0.10 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) 1.90 BSC NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193 S6 TSOT-23 0302 REV B 3483fb 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. 11 LT3483 TYPICAL APPLICATIONS 3.6V to –22V DC/DC Converter VIN 3.6V 75 C2 0.1μF L1 10μH 3.6V to –22V Converter Efficiency and Power Loss 1000 D1 EFFICIENCY D VIN C1 4.7μF VOUT –22V 8mA LT3483 R1 2.2M 5pF SHDN FB GND C3 1μF EFFICIENCY (%) SW 70 100 65 10 POWER LOSS 60 C1: TAIYO YUDEN LMK316BJ475MD C2: TAIYO YUDEN TMK107BJ104 (X5R) C3: TAIYO YUDEN TMK316BJ105MD D1: PHILIPS PMEG3002AEB L1: MURATA LQH2MCN100K02L POWER LOSS (mW) RS 30Ω 1 3483 TA02a 55 0.1 1 0.1 10 LOAD CURRENT (mA) 3483 TA02b –5V DC/DC Converter L1A 10μH • 75 L1B 10μH 10Ω • 70 SW VIN C1 4.7μF VOUT –5V D LT3483 22pF 511k SHDN FB GND C2 10μF EFFICIENCY (%) VIN 1nF – 5V Efficiency VIN = 5V 65 VIN = 12V 60 C1: TAIYO YUDEN EMK316BJ475ML C2: TAIYO YUDEN JMK316BJ106ML L1A, L1B: WURTH 744876100 3483 TA03a 55 0.1 1 10 LOAD CURRENT (mA) 100 3483 TA03b RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1617/LT1617-1 350mA/100mA (ISW) High Efficiency Micropower Inverting DC/DC Converter VIN: 1.2V to 15V, VOUT(MAX) = –34V, IQ = 20μA, ISD < 1μA ThinSOT Package LT1931/LT1931A 1A (ISW), 1.2MHz/2.2MHz, High Efficiency Micropower Inverting DC/DC Converter VIN: 2.6V to 16V, VOUT(MAX) = –34V, IQ = 5.8mA, ISD < 1μA ThinSOT Package LT1945 Dual Output, Boost/Inverter, 350mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter VIN: 1.2V to 15V, VOUT(MAX) = ±34V, IQ = 40μA, ISD < 1μA, MS10 Package LT3463 Dual Output, Boost/Inverter, 250mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter with Integrated Schottky Diodes VIN: 2.3V to 15V, VOUT(MAX) = ±40V, IQ = 40μA, ISD < 1μA DFN Package LT3464 85mA (ISW), High Efficiency Step-Up DC/DC Converter with Integrated Schottky and PNP Disconnect VIN: 2.3V to 10V, VOUT(MAX) = 34V, IQ = 25μA, ISD < 1μA ThinSOT Package LT3472 Boost (350mA) and Inverting (400mA) DC/DC Converter for CCD Bias with Integrated Schottkys VIN: 2.3V to 15V, VOUT(MAX) = ±40V, IQ = 2.8mA, ISD < 1μA DFN Package 3483fb 12 Linear Technology Corporation LT 0508 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2004