LT3483 Inverting Micropower DC/DC Converter with Schottky in ThinSOT Package U FEATURES DESCRIPTIO ■ 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. ■ ■ ■ ■ ■ ■ ■ ■ ■ 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 Package U APPLICATIO S ■ ■ ■ ■ LCD Bias Handheld Computers Battery Backup Digital Cameras OLED Bias The LT3483 is available in the low profile (1mm) SOT-23 (ThinSOTTM) package. , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. Patent pending. U ■ TYPICAL APPLICATIO Efficiency and Power Loss 3.6V to –8V DC/DC Converter 75 VIN 3.6V 0.22µF 10µH 4.7µF D LT3483 SHDN FB GND 5pF 806k 2.2µF EFFICIENCY (%) VIN VOUT –8V 25mA 100 65 10 POWER LOSS 60 POWER LOSS (mW) SW EFFICIENCY 70 10Ω 1000 VIN = 3.6V 1 3483 TA01a 55 0.1 1 10 LOAD CURRENT (mA) 0.1 100 3483 TA01b 3483f 1 LT3483 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) VIN Voltage ............................................................. 16V SW Voltage ............................................................. 40V D Voltage .............................................................. –40V FB Voltage ............................................................. 2.5V SHDN Voltage ......................................................... 16V Operating Ambient Temperature Range (Note 2) .................................................. – 40°C to 85°C Junction Temperature .......................................... 125°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300°C ORDER PART NUMBER TOP VIEW LT3483ES6 6 VIN SW 1 GND 2 5D FB 3 4 SHDN S6 PACKAGE 6-LEAD PLASTIC TSOT-23 S6 PART MARKING TJMAX = 125°C, θJA = 256°C/W IN FREE AIR θJA = 120°C/W ON BOARD OVER GROUND PLANE LTBKX Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VIN = 3.6V, VSHDN = 3.6V unless otherwise specified. PARAMETER CONDITIONS MIN VIN Operating Range TYP MAX 16 V 2 2.4 V mV 2.5 VIN Undervoltage Lockout FB Falling ● 0 5 12 FB Output Current (Note 3) FB = VFB – 5mV ● –10.15 –10 –9.75 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 FB Comparator Trip Voltage to GND (VFB) 10 Switch Off-Time 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 50 µA %/V SHDN Input High Voltage 230 mA mV 1 µA 4 µA 0.64 V 0.4 V 10 µA 1.5 SHDN Pin Current Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC3483E is guaranteed to meet 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. ns 200 SHDN Input Low Voltage µA 0.07 300 Switch Current Limit µA mV 1 40 UNITS V 6 Note 3: Current flows out of the pin. 3483f 2 LT3483 U W TYPICAL PERFOR A CE CHARACTERISTICS VFB Current VFB Voltage Switch Off Time 12 10.2 400 350 VFB VOLTAGE (mV) VFB CURRENT (µA) 10.0 SWITCH OFF TIME (ns) 9 10.1 6 3 9.9 300 250 200 150 100 50 9.8 –50 –20 40 10 TEMPERATURE (°C) 70 0 –50 100 –20 40 10 TEMPERATURE (°C) 70 Switch Current Limit Quiescent Current 190 180 70 100 SHDN Pin Bias Current 10 SHDN PIN BIAS CURRENT (µA) QUIESCENT CURRENT (µA) SWITCH CURRENT LIMIT (mA) 220 200 10 40 TEMPERATURE (°C) 3483 G03 50 230 210 –20 3483 G02 3483 G01 170 –50 0 –50 100 40 30 20 10 TA = 25°C 8 6 4 2 NOT SWITCHING VFB = –0.05V –20 10 40 TEMPERATURE (°C) 70 100 0 –50 –20 40 10 TEMPERATURE (°C) 3483 G04 70 100 3483 G05 0 0 8 4 12 SHDN PIN VOLTAGE (V) 16 3483 G06 U U U PI FU CTIO S SW: Switch. Connect to external inductor L1 and positive terminal of transfer capacitor. GND: Ground. FB: Feedback. Place resistor to negative output here. Set resistor value R1 = VOUT/10µA. SHDN: Shutdown. Connect to GND to turn device off. Connect to supply to turn device on. D: 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). VIN: Input Supply. Must be locally bypassed with 1µF or greater. 3483f 3 LT3483 W BLOCK DIAGRA 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 3483 BD OPTIONAL CHARGE PUMP CONFIGURATION. L1B REPLACED WITH: D2 D R2 VOUT U OPERATIO 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. 3483f 4 LT3483 U W U U APPLICATIO S I FOR ATIO CHOOSING A REGULATOR TOPOLOGY Inductor Selection Inverting Charge Pump 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 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. 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. Table 1. Recommended Inductors L PART (µH) LQH2MCN4R7M02L 4.7 LQH2MCN6R8M02L 6.8 LQH2MCN100M02L 10 SDQ12 10 Coupled 15 Inductor 744876 10 Coupled Inductor MAX IDC (mA) 300 255 225 980 780 DCR (Ω) 0.84 1.0 1.2 0.72 1.15 550 0.46 HEIGHT (mm) MANUFACTURER 0.95 Murata www.murata.com 1.2 1.2 Cooper Electronics Tech www.cooperet.com Würth Elektronik www.we-online.com 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. 3483f 5 LT3483 U W U U APPLICATIO S I FOR ATIO 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 to 4.7µF. The following formula is useful to estimate the output capacitor value needed: COUT L • ISW2 = – VOUT • ∆VOUT where ISW = 0.25A and ∆VOUT = 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 URL AVX www.avxcorp.com Kemet www.kemet.com Murata www.murata.com Taiyo Yuden www.tyuden.com 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. Board Layout Considerations 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 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. Suggested Layout (SOT-23) for Inverting Charge Pump + MANUFACTURER 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. GND CIN L1 Setting the Output Voltage CFLY VIN The output voltage is programmed using one feedback resistor according to the following formula: V R1 = – OUT 10µA 6 2 5 3 4 COUT R1 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. 1 SHDN VOUT 3483 AI01 3483f 6 LT3483 U TYPICAL APPLICATIO 3.6V to –8V DC/DC Converter Low Profile, Small Footprint VIN 3.6V Switching Waveform C2 0.22µF L1 10µH D1 10Ω SW VIN C1 4.7µF D LT3483 R1 806k 5pF VOUT –8V 25mA C3 2.2µF VOUT 20mV/DIV ISW 100mA/DIV SHDN FB GND 2µs/DIV C1: MURATA GRM219R61A475KE34B C2: TAIYO YUDEN LMK107BJ224 C3: MURATA GRM219R61C225KA88B D1: PHILIPS PMEG2005EB L1: MURATA LQH2MCN100K02L 3483 TA04b 3483 TA04a U PACKAGE DESCRIPTIO S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 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 NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 0.09 – 0.20 (NOTE 3) 1.90 BSC S6 TSOT-23 0302 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 3483f 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 LT3483 U TYPICAL APPLICATIO S 3.6V to –22V DC/DC Converter C2 0.1µF VIN 3.6V 75 EFFICIENCY 70 VOUT –22V 8mA D VIN LT3483 R1 2.2M 5pF C3 1µF SHDN FB GND 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 SW C1 4.7µF 1000 D1 EFFICIENCY (%) L1 10µH 3.6V to –22V Converter Efficiency and Power Loss 1 3483 TA02a 55 0.1 0.1 10 1 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 C2 10µF SHDN FB GND 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 3483f 8 Linear Technology Corporation LT/TP 1004 1K • PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2004