TYPICAL APPLICATIO. LT3483 Inverting Micropower DC/DC Converter with Schottky in ThinSOT Package FEATURES DESCRIPTIO APPLICATIO S

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1 Inverting Micropower DC/DC Converter with Schottky in ThinSOT Package FEATRES Internal 4V Schottky Diode One Resistor Feedback (Other Resistor Inside) Internal 4V, ma Power Switch Generates Regulated Negative Outputs to 38V Low Quiescent Current: 4µA in Active Mode <µa in Shutdown Mode Low V CESAT Switch: mv at 5mA Wide Input Range:.5V to V ses Small Surface Mount Components Output Short-Circuit Protected Available in a -Lead SOT-3 Package APPLICATIO S LCD Bias Handheld Computers Battery Backup Digital Cameras OLED Bias 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 4mm. The device features a quiescent current of only 4µA at no load, which further reduces to.µa 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 µa feedback current enables one resistor feedback and virtually eliminates feedback loading of the output. The 4V switch enables voltage outputs up to 38V to be generated without the use of costly transformers. The s low 3ns off-time permits the use of tiny low profile inductors and capacitors to minimize footprint and cost in space-conscious portable applications. The is available in the low profile (mm) SOT-3 (ThinSOT TM ) package., LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. Patent pending. TYPICAL APPLICATIO 3.V to 8V DC/DC Converter Efficiency and Power Loss 3.V 4.7µF µh.µf D SHDN FB 5pF Ω 8k.µF 8V 5mA EFFICIENCY (%) = 3.V EFFICIENCY POWER LOSS POWER LOSS (mw) 3483 TAa 55. LOAD CRRENT (ma) 3483 TAb.

2 ABSOLTE AXI RATI GS W W W (Note ) Voltage... V Voltage... 4V D Voltage... 4V FB Voltage....5V SHDN Voltage... V Operating Ambient Temperature Range (Note )... 4 C to 85 C Junction Temperature... 5 C Storage Temperature Range... 5 C to 5 C Lead Temperature (Soldering, sec)... 3 C W PACKAGE/ORDER I FOR ATIO FB 3 TOP VIEW S PACKAGE -LEAD PLASTIC TSOT-3 5 D 4 SHDN T JMAX = 5 C, θ JA = 5 C/W IN FREE AIR θ JA = C/W ON BOARD OVER GROND PLANE ORDER PART NMBER ES S PART MARKING 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 T A = 5 C. = 3.V, V SHDN = 3.V unless otherwise specified. PARAMETER CONDITIONS MIN TYP MAX NITS Operating Range.5 V ndervoltage Lockout.4 V FB Comparator Trip Voltage to (V FB ) FB Falling 5 mv FB Output Current (Note 3) FB = V FB 5mV µa FB Comparator Hysteresis FB Rising mv Quiescent Current in Shutdown V SHDN = µa Quiescent Current (Not Switching) FB =.5V 4 5 µa I FB Line Regulation.5V V.7 %/V Switch Off-Time 3 ns Switch Current Limit 7 3 ma Switch V CESAT I = 5mA to mv Switch Leakage Current = 4V µa Rectifier Leakage Current D = 4V 4 µa Rectifier Forward Drop I D = 5mA to.4 V SHDN Input Low Voltage.4 V SHDN Input High Voltage.5 V SHDN Pin Current µa Note : Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note : The LTC3483E is guaranteed to meet specifications from C to 7 C. Specifications over the 4 C to 85 C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Current flows out of the pin.

3 TYPICAL PERFOR A CE CHARACTERISTICS W. V FB Current V FB Voltage 4 Switch Off Time 35 V FB CRRENT (µa) V FB VOLTAGE (mv) 9 3 ITCH OFF TIME (ns) TEMPERATRE ( C) TEMPERATRE ( C) TEMPERATRE ( C) 3483 G 3483 G 3483 G3 3 Switch Current Limit Quiescent Current SHDN Pin Bias Current 5 TA = 5 C ITCH CRRENT LIMIT (ma) TEMPERATRE ( C) QIESCENT CRRENT (µa) 4 3 NOT ITCHING V FB =.5V TEMPERATRE ( C) SHDN PIN BIAS CRRENT (µa) SHDN PIN VOLTAGE (V) 3483 G G G PI F CTIO S : Switch. Connect to external inductor L and positive terminal of transfer capacitor. : Ground. FB: Feedback. Place resistor to negative output here. Set resistor value R = /µa. SHDN: Shutdown. Connect to 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 L (flyback configuration) or to cathode of external Schottky diode (inverting charge pump configuration). : Input Supply. Must be locally bypassed with µf or greater. 3

4 + BLOCK DIAGRA W LA C FLY LB C OT 5.5V REFERENCE 3ns DELAY D 5k S Q R 3 FB + A3 R Q A mv Q D 5mV.Ω.Ω + A OPTIONAL CHARGE PMP CONFIGRATION. LB REPLACED WITH: D R D 3483 BD OPERATIO The 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 V, comparator A3 disables most of the internal circuitry. Output current is then provided by external capacitor C OT, which slowly discharges until the voltage at the FB pin goes above the hysteresis point of A3. Typical hysteresis at the FB pin is mv. A3 then enables the internal circuitry, turns on power switch Q, and the currents in external inductors LA and LB begin to ramp up. Once the switch current reaches ma, comparator A resets the latch, which turns off Q after about 8ns. Inductor current flows through the internal Schottky D to, charging the flying capacitor. Once the 3ns off-time has elapsed, and internal diode current drops below 5mA (as detected by comparator A), Q turns on again and ramps up to ma. This switching action continues until the output capacitor charge is replenished (until the FB pin decreases to V), then A3 turns off the internal circuitry and the cycle repeats. The inverting charge pump topology replaces LB with the series combination D and R. 4

5 APPLICATIO S I FOR ATIO W CHOOSING A REGLATOR 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 is greater than. Negative outputs to 38V can be produced with the in this configuration. For cases where the magnitude of is less than or equal to, use a -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. The purpose of this resistor is to smooth/reduce the current spike in the flying capacitor when the switch turns on. A Ω 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 using the flyback is less than can be obtained with the charge pump it is reduced from 38V by the magnitudes of and ringing at the switch node. nder a short-circuit condition at the output, a proprietary technique limits the switch current and prevents damage to the even with supply voltage as high as V. As an option, a.47µf capacitor may be added between terminals D and of to suppress ringing at. Inductor Selection Several recommended inductors that work well with the are listed in Table, 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.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 µh 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. Table. Recommended Inductors MAX L I DC DCR HEIGHT PART (µh) (ma) (Ω) (mm) MANFACTRER LQHMCN4R7ML Murata LQHMCNR8ML LQHMCNML 5. SDQ Cooper Electronics Coupled Tech Inductor Würth Elektronik Coupled Inductor Capacitor Selection The small size and low ESR of ceramic capacitors make them ideal for applications. se 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 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 pin is recommended where the distance to the power supply or battery could be more than a couple inches. Otherwise, a µf is adequate. 5

6 APPLICATIO S I FOR ATIO W A capacitor in parallel with feedback resistor R is recommended to reduce the output voltage ripple. se a 5pF capacitor for the inverting charge pump, and a pf value for the inverting flyback or other dual inductor configurations. Output voltage ripple can be reduced to mv 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 µf capacitor. The inverting charge pump utilizes values ranging from.µf to 4.7µF. The following formula is useful to estimate the output capacitor value needed: C OT L I = V V OT OT where I =.5A and = 3mV. The flying capacitor in the inverting charge pump configuration ranges from.µf to.47µf. Multiply the value predicted by the above equation for C OT by / to determine the value needed for the flying capacitor. Table. Recommended Ceramic Capacitor Manufacturers MANFACTRER RL AVX Kemet Murata Taiyo Yuden Setting the Output Voltage The output voltage is programmed using one feedback resistor according to the following formula: VOT R= µ A Conditions that increase inrush current include a larger, more abrupt voltage step at, 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.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, 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 and D pins have sharp rising and falling edges. Minimize the length and area of all traces connected to the 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-3) for Inverting Charge Pump C OT C FLY 3 C IN + L 5 4 Inrush Current R When 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 AI SHDN

7 TYPICAL APPLICATIO 3.V to 8V DC/DC Converter Low Profile, Small Footprint 3.V C 4.7µF L µh C.µF D SHDN FB D 5pF Ω R 8k 8V 5mA C3.µF mv/div I ma/div Switching Waveform C: MRATA GRM9RA475KE34B C: TAIYO YDEN LMK7BJ4 C3: MRATA GRM9RC5KA88B D: PHILIPS PMEG5EB L: MRATA LQHMCNKL 3483 TA4a µs/div 3483 TA4b PACKAGE DESCRIPTIO S Package -Lead Plastic TSOT-3 (Reference LTC DWG # 5-8-3). MAX.95 REF.9 BSC (NOTE 4). REF 3.85 MAX. REF.4 MIN.8 BSC.5.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOT PER IPC CALCLATOR.95 BSC.3.45 PLCS (NOTE 3).8.9. BSC DATM A. MAX REF NOTE:. DIMENSIONS ARE IN MILLIMETERS. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLSIVE OF PLATING.9..9 BSC (NOTE 3) S TSOT DIMENSIONS ARE EXCLSIVE OF MOLD FLASH AND METAL BRR 5. MOLD FLASH SHALL NOT EXCEED.54mm. JEDEC PACKAGE REFERENCE IS MO-93 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

8 TYPICAL APPLICATIO S 3.V to V DC/DC Converter 3.V to V Converter Efficiency and Power Loss 3.V C 4.7µF L µh C.µF D SHDN FB D 5pF R S 3Ω R.M V 8mA C3 µf EFFICIENCY (%) EFFICIENCY POWER LOSS POWER LOSS (mw) C: TAIYO YDEN LMK3BJ475MD C: TAIYO YDEN TMK7BJ4 (X5R) C3: TAIYO YDEN TMK3BJ5MD D: PHILIPS PMEG3AEB L: MRATA LQHMCNKL 3483 TAa 55. LOAD CRRENT (ma) TAb 5V DC/DC Converter 5V Efficiency C 4.7µF LA µh nf Ω D SHDN FB LB µh pf 5k C µf 5V EFFICIENCY (%) = 5V = V C: TAIYO YDEN EMK3BJ475ML C: TAIYO YDEN JMK3BJML LA, LB: WRTH TA3a 55. LOAD CRRENT (ma) 3483 TA3b RELATED PARTS PART NMBER DESCRIPTION COMMENTS LT7/LT7-35mA/mA (I ) High Efficiency :.V to 5V, (MAX) = 34V, I Q = µa, I SD < µa Micropower Inverting DC/DC Converter ThinSOT Package LT93/LT93A A (I ),.MHz/.MHz, High Efficiency :.V to V, (MAX) = 34V, I Q = 5.8mA, I SD < µa Micropower Inverting DC/DC Converter ThinSOT Package LT945 Dual Output, Boost/Inverter, 35mA (I ), Constant :.V to 5V, (MAX) = ±34V, I Q = 4µA, I SD < µa, Off-Time, High Efficiency Step-p DC/DC Converter MS Package LT343 Dual Output, Boost/Inverter, 5mA (I ), Constant :.3V to 5V, (MAX) = ±4V, I Q = 4µA, I SD < µa Off-Time, High Efficiency Step-p DC/DC Converter DFN Package with Integrated Schottky Diodes LT344 85mA (I ), High Efficiency Step-p DC/DC Converter :.3V to V, (MAX) = 34V, I Q = 5µA, I SD < µa with Integrated Schottky and PNP Disconnect ThinSOT Package LT347 Boost (35mA) and Inverting (4mA) DC/DC Converter :.3V to 5V, (MAX) = ±4V, I Q =.8mA, I SD < µa for CCD Bias with Integrated Schottkys DFN Package 8 Linear Technology Corporation 3 McCarthy Blvd., Milpitas, CA (48) 43-9 FAX: (48) LT/TP 4 K PRINTED IN THE SA LINEAR TECHNOLOGY CORPORATION 4