LT1615/LT1615-1 Micropower Step-Up DC/DC Converters in ThinSOT U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ The LT®1615/LT1615-1 are micropower step-up DC/DC converters in a 5-lead low profile (1mm) ThinSOT package. The LT1615 is designed for higher power systems with a 350mA current limit and an input voltage range of 1.2V to 15V, whereas the LT1615-1 is intended for lower power and single-cell applications with a 100mA current limit and an extended input voltage range of 1V to 15V. Otherwise, the two devices are functionally equivalent. Both devices feature a quiescent current of only 20µA at no load, which further reduces to 0.5µA in shutdown. A current limited, fixed off-time control scheme conserves operating current, resulting in high efficiency over a broad range of load current. The 36V switch allows high voltage outputs up to 34V to be easily generated in a simple boost topology without the use of costly transformers. The LT1615’s low off-time of 400ns permits the use of tiny, low profile inductors and capacitors to minimize footprint and cost in space-conscious portable applications. Low Quiescent Current: 20µA in Active Mode <1µA in Shutdown Mode Operates with VIN as Low as 1V Low VCESAT Switch: 250mV at 300mA Uses Small Surface Mount Components High Output Voltage: Up to 34V Low Profile (1mm) ThinSOTTM Package U APPLICATIO S ■ ■ ■ ■ LCD Bias Handheld Computers Battery Backup Digital Cameras , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. U TYPICAL APPLICATIO 1-Cell Li-Ion to 20V Converter for LCD Bias Efficiency 85 L1 10µH VIN 2.5V TO 4.2V D1 80 20V 12mA VIN = 4.2V VIN SW R1 2M C2 1µF LT1615 FB SHDN C1 4.7µF GND C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN TMK316BJ105 D1: MOTOROLA MBR0530 L1: MURATA LQH3C100K24 R2 130k EFFICIENCY (%) 75 VIN = 2.5V 70 VIN = 3.3V 65 60 1615/-1 TA01 55 50 0.1 0.3 1 3 10 LOAD CURRENT (mA) 30 1615/-1 TA01a sn16151 16151fas 1 LT1615/LT1615-1 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) VIN, SHDN Voltage ................................................... 15V SW Voltage .............................................................. 36V FB Voltage .................................................................VIN Current into FB Pin ................................................. 1mA Junction Temperature ........................................... 125°C Operating Temperature Range (Note 2) .. – 40°C to 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C ORDER PART NUMBER LT1615ES5 LT1615ES5-1 LT1615IS5 LT1615IS5-1 TOP VIEW SW 1 5 VIN GND 2 FB 3 4 SHDN S5 PACKAGE 5-LEAD PLASTIC SOT-23 S5 PART MARKING TJMAX = 125°C, θJA = 256°C/W LTIZ LTKH LTXZ LTBHT 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. VIN = 1.2V, VSHDN = 1.2V unless otherwise noted. PARAMETER CONDITIONS Minimum Input Voltage LT1615-1 LT1615 Quiescent Current Not Switching VSHDN = 0V FB Comparator Trip Point MIN ● 1.205 FB Comparator Hysteresis TYP MAX UNITS 1.0 1.2 V V 20 30 1 µA µA 1.23 1.255 V 8 mV Output Voltage Line Regulation 1.2V < VIN < 12V FB Pin Bias Current (Note 3) VFB = 1.23V Switch Off Time VFB > 1V VFB < 0.6V 400 1.5 Switch VCESAT ISW = 70mA (LT1615-1) ISW = 300mA (LT1615) 85 250 120 350 mV mV Switch Current Limit LT1615-1 LT1615 100 350 125 400 mA mA SHDN Pin Current VSHDN = 1.2V VSHDN = 5V 2 8 3 12 µA µA SHDN Input Voltage High ● 75 300 0.05 0.1 %/V 30 80 nA 0.9 V SHDN Input Voltage Low Switch Leakage Current ns µs Switch Off, VSW = 5V Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT1615E and LT1615E-1 are 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, 0.01 0.25 V 5 µA characterization and correlation with statistical process controls. The LT1615I/LT1615I-1 is guaranteed to meet performance specifications over the –40°C to 85°C operating temperature range. Note 3: Bias current flows into the FB pin. sn16151 16151fas 2 LT1615/LT1615-1 U W TYPICAL PERFOR A CE CHARACTERISTICS Switch Saturation Voltage (VCESAT) Feedback Pin Voltage and Bias Current 0.60 Quiescent Current 1.25 50 25 40 23 VFB = 1.23V NOT SWITCHING FEEDBACK VOLTAGE (V) 1.24 0.45 ISWITCH = 500mA 0.40 0.35 0.30 ISWITCH = 300mA 0.25 0.20 VOLTAGE 1.23 30 CURRENT 1.22 20 1.21 10 BIAS CURRENT (nA) SWITCH VOLTAGE (V) 0.50 QUIESCENT CURRENT (µA) 0.55 21 VIN = 12V 19 VIN = 1.2V 17 0.15 –25 0 25 50 TEMPERATURE (°C) 75 1.20 –50 100 –25 0 25 50 TEMPERATURE (°C) 1615/-1 G01 400 PEAK CURRENT (mA) VIN = 1.2V VIN = 12V 350 250 –50 75 300 VIN = 1.2V LT1615 250 200 150 LT1615-1 100 25 VIN = 12V VIN = 12V 100 VIN = 1.2V 300 0 25 50 TEMPERATURE (°C) Shutdown Pin Current 350 500 450 –25 1615/-1 G03 Switch Current Limit 550 400 15 –50 0 100 1615/-1 G02 Switch Off Time SWITCH OFF TIME (ns) 75 SHUTDOWN PIN CURRENT (µA) 0.10 –50 20 15 25°C 10 100°C 5 50 –25 0 25 50 TEMPERATURE (°C) 75 100 0 –50 0 –25 0 25 50 TEMPERATURE (°C) 1615/-1 G04 75 100 1615/-1 G05 0 5 10 SHUTDOWN PIN VOLTAGE (V) 15 1615/-1 G03 U U U PI FU CTIO S SW (Pin 1): Switch Pin. This is the collector of the internal NPN power switch. Minimize the metal trace area connected to this pin to minimize EMI. GND (Pin 2): Ground. Tie this pin directly to the local ground plane. SHDN (Pin 4): Shutdown Pin. Tie this pin to 0.9V or higher to enable the device. Tie below 0.25V to turn off the device. VIN (Pin 5): Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible. FB (Pin 3): Feedback Pin. Set the output voltage by selecting values for R1 and R2 (see Figure 1): V R1 = R2 OUT − 1 1.23 sn16151 16151fas 3 LT1615/LT1615-1 W BLOCK DIAGRA D1 L1 VOUT VIN C1 5 VIN R5 40k 4 SHDN 1 C2 SW R6 40k + A1 ENABLE VOUT – R1 (EXTERNAL) R2 (EXTERNAL) FB 3 Q1 Q2 X10 400ns ONE-SHOT Q3 DRIVER R3 30k RESET + R4 140k 0.12Ω A2 – 42mV* 2 GND 1615/-1 BD * 12mV FOR LT1615-1 Figure 1. LT1615 Block Diagram U OPERATIO The LT1615 uses a constant off-time control scheme to provide high efficiencies over a wide range of output current. Operation can be best understood by referring to the block diagram in Figure 1. Q1 and Q2 along with R3 and R4 form a bandgap reference used to regulate the output voltage. When the voltage at the FB pin is slightly above 1.23V, comparator A1 disables most of the internal circuitry. Output current is then provided by capacitor C2, which slowly discharges until the voltage at the FB pin drops below the lower hysteresis point of A1 (typical hysteresis at the FB pin is 8mV). A1 then enables the internal circuitry, turns on power switch Q3, and the current in inductor L1 begins ramping up. Once the switch current reaches 350mA, comparator A2 resets the oneshot, which turns off Q3 for 400ns. L1 then delivers current to the output through diode D1 as the inductor current ramps down. Q3 turns on again and the inductor current ramps back up to 350mA, then A2 resets the oneshot, again allowing L1 to deliver current to the output. This switching action continues until the output voltage is charged up (until the FB pin reaches 1.23V), then A1 turns off the internal circuitry and the cycle repeats. The LT1615 contains additional circuitry to provide protection during start-up and under short-circuit conditions. When the FB pin voltage is less than approximately 600mV, the switch off-time is increased to 1.5µs and the current limit is reduced to around 250mA (70% of its normal value). This reduces the average inductor current and helps minimize the power dissipation in the LT1615 power switch and in the external inductor and diode. The LT1615-1 operates in the same manner, except the switch current is limited to 100mA (the A2 reference voltage is 12mV instead of 42mV). sn16151 16151fas 4 LT1615/LT1615-1 U U W U APPLICATIO S I FOR ATIO Choosing an Inductor Several recommended inductors that work well with the LT1615 and LT1615-1 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. Use the equations and recommendations in the next few sections to find the correct inductance value for your design. Table 1. Recommended Inductors PART VALUE (µH) MAX DCR (Ω) VENDOR LQH3C4R7 LQH3C100 LQH3C220 4.7 10 22 0.26 0.30 0.92 Murata (814) 237-1431 www.murata.com CD43-4R7 CD43-100 CDRH4D18-4R7 CDRH4D18-100 4.7 10 4.7 10 0.11 0.18 0.16 0.20 Sumida (847) 956-0666 www.sumida.com DO1608-472 DO1608-103 DO1608-223 4.7 10 22 0.09 0.16 0.37 Coilcraft (847) 639-6400 www.coilcraft.com VIN value in the above equation. For most systems with output voltages below 7V, a 4.7µH inductor is the best choice, even though the equation above might specify a smaller value. This is due to the inductor current overshoot that occurs when very small inductor values are used (see Current Limit Overshoot section). For higher output voltages, the formula above will give large inductance values. For a 2V to 20V converter (typical LCD Bias application), a 21µH inductor is called for with the above equation, but a 10µH inductor could be used without excessive reduction in maximum output current. Inductor Selection—SEPIC Regulator The formula below calculates the approximate inductor value to be used for a SEPIC regulator using the LT1615. As for the boost inductor selection, a larger or smaller value can be used. V +V L = 2 OUT D ILIM tOFF Inductor Selection—Boost Regulator The formula below calculates the appropriate inductor value to be used for a boost regulator using the LT1615 or LT1615-1 (or at least provides a good starting point). This value provides a good tradeoff in inductor size and system performance. Pick a standard inductor close to this value. A larger value can be used to slightly increase the available output current, but limit it to around twice the value calculated below, as too large of an inductance will increase the output voltage ripple without providing much additional output current. A smaller value can be used (especially for systems with output voltages greater than 12V) to give a smaller physical size. Inductance can be calculated as: L= VOUT − VIN(MIN) + VD ILIM tOFF where VD = 0.4V (Schottky diode voltage), ILIM = 350mA or 100mA, and tOFF = 400ns; for designs with varying VIN such as battery powered applications, use the minimum Current Limit Overshoot For the constant off-time control scheme of the LT1615, the power switch is turned off only after the 350mA (or 100mA) current limit is reached. There is a 100ns delay between the time when the current limit is reached and when the switch actually turns off. During this delay, the inductor current exceeds the current limit by a small amount. The peak inductor current can be calculated by: VIN(MAX) − VSAT IPEAK = ILIM + 100ns L Where VSAT = 0.25V (switch saturation voltage). The current overshoot will be most evident for systems with high input voltages and for systems where smaller inductor values are used. This overshoot can be beneficial as it helps increase the amount of available output current for smaller inductor values. This will be the peak current seen by the inductor (and the diode) during normal operation. For designs using small inductance values (especially at sn16151 16151fas 5 LT1615/LT1615-1 U W U U APPLICATIO S I FOR ATIO input voltages greater than 5V), the current limit overshoot can be quite high. Although it is internally current limited to 350mA, the power switch of the LT1615 can handle larger currents without problem, but the overall efficiency will suffer. Best results will be obtained when IPEAK is kept below 700mA for the LT1615 and below 400mA for the LT1615-1. Capacitor Selection Low ESR (Equivalent Series Resistance) capacitors should be used at the output to minimize the output ripple voltage. Multilayer ceramic capacitors are the best choice, as they have a very low ESR and are available in very small packages. Their small size makes them a good companion to the LT1615’s SOT-23 package. Solid tantalum capacitors (like the AVX TPS, Sprague 593D families) or OS-CON capacitors can be used, but they will occupy more board area than a ceramic and will have a higher ESR. Always use a capacitor with a sufficient voltage rating. Ceramic capacitors also make a good choice for the input decoupling capacitor, which should be placed as close as possible to the LT1615. A 4.7µF input capacitor is sufficient for most applications. Table 2 shows a list of several capacitor manufacturers. Consult the manufacturers for more detailed information and for their entire selection of related parts. Diode Selection For most LT1615 applications, the Motorola MBR0520 surface mount Schottky diode (0.5A, 20V) is an ideal choice. Schottky diodes, with their low forward voltage drop and fast switching speed, are the best match for the LT1615. For higher output voltage applications the 30V MBR0530 can be used. Many different manufacturers make equivalent parts, but make sure that the component is rated to handle at least 0.35A. For LT1615-1 applications, a Philips BAT54 or Central Semiconductor CMDSH-3 works well. Lowering Output Voltage Ripple Using low ESR capacitors will help minimize the output ripple voltage, but proper selection of the inductor and the output capacitor also plays a big role. The LT1615 provides energy to the load in bursts by ramping up the inductor current, then delivering that current to the load. If too large of an inductor value or too small of a capacitor value is used, the output ripple voltage will increase because the capacitor will be slightly overcharged each burst cycle. To reduce the output ripple, increase the output capacitor value or add a 4.7pF feed-forward capacitor in the feedback network of the LT1615 (see the circuits in the Typical Applications section). Adding this small, inexpensive 4.7pF capacitor will greatly reduce the output voltage ripple. Table 2. Recommended Capacitors CAPACITOR TYPE VENDOR Ceramic Taiyo Yuden (408) 573-4150 www.t-yuden.com Ceramic AVX (803) 448-9411 www.avxcorp.com Ceramic Murata (714) 852-2001 www.murata.com sn16151 16151fas 6 LT1615/LT1615-1 U TYPICAL APPLICATIO S 2-Cell to 3.3V Converter Efficiency 2-Cell to 3.3V Boost Converter L1 4.7µH 90 D1 5 1 VIN SW 3.3V 60mA FB SHDN C2 22µF 3 GND C1 4.7µF VIN = 3V 80 1M LT1615 4 85 4.7pF EFFICIENCY (%) VIN 1.5V TO 3V 604k 2 75 VIN = 1.5V 70 65 60 C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN JMK325BJ226 L1: MURATA LQH3C4R7M24 D1: MOTOROLA MBR0520 (408) 573-4150 (408) 573-4150 (814) 237-1431 (800) 441-2447 1615/-1 TA03 55 50 0.1 1 10 LOAD CURRENT (mA) 100 1615/-1 TA03a 4-Cell to 5V SEPIC Converter 1-Cell Li-Ion to 3.3V SEPIC Converter C3 1µF L1 10µH VIN 2.5V TO 4.2V 5 1 VIN SW 3.3V 50mA LT1615 4 FB SHDN 1M C2 10µF 3 GND C1 4.7µF VIN 3V TO 6V 4.7pF L2 10µH (408) 573-4150 (408) 573-4150 (408) 573-4150 (814) 237-1431 (800) 441-2447 L1 22µH C1 4.7µF SW SHDN 1 VIN SW FB GND 1M C2 10µF 3 GND 324k 2 C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN JMK316BJ106 C3: TAIYO YUDEN JMK107BJ105 L1, L2: MURATA LQH3C100K24 D1: MOTOROLA MBR0520 1615/-1 TA07 35V 500µA (408) 573-4150 (408) 573-4150 (408) 573-4150 (814) 237-1431 (800) 441-2447 L1 22µH VIN 1V TO 1.5V 10M 1615/-1 TA07 (408) 573-4150 (408) 573-4150 (814) 237-1431 (800) 441-2447 4 C1 4.7µF 2 1615/-1 TA09 D1 5 1 VIN SW 3.3V 15mA 4.7pF 1M C2 10µF LT1615-1 C2 1µF 3 365k C1: TAIYO YUDEN EMK316BJ475 C2: TAIYO YUDEN GMK316BJ105 L1: MURATA LQH3C220K24 D1: MOTOROLA MBR0540 4.7pF L2 10µH FB D1 5 SHDN VIN 5V 40mA 1-Cell to 3.3V Boost Converter LT1615-1 4 1 C1 4.7µF 604k PIN Diode Driver VIN 1V TO 6V 5 D1 LT1615 4 2 C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN JMK316BJ106 C3: TAIYO YUDEN JMK107BJ105 L1, L2: MURATA LQH3C100K24 D1: MOTOROLA MBR0520 C3 1µF L1 10µH D1 FB SHDN 3 GND 604k 2 C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN JMK316BJ106 L1: MURATA LQH3C220K24 D1: CENTRAL SEMICONDUCTOR CMDSH-3 (408) 573-4150 (408) 573-4150 (814) 237-1431 (516) 435-1110 1615/-1 TA04 sn16151 16151fas 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 LT1615/LT1615-1 U TYPICAL APPLICATIO S ±20V Dual Output Converter with Output Disconnect D3 –20V 4mA C3 1µF D2 C4 1µF C5 1µF L1 10µH VIN 1.5V TO 5V 5 D1 20V 4mA 1 VIN 4.7pF SW D4 2M C2 1µF LT1615 4 FB SHDN 3 GND C1 4.7µF 130k 2 C1: TAIYO YUDEN LMK316BJ475 C2, C3, C4: TAIYO YUDEN TMK316BJ105 C5: TAIYO YUDEN LMK212BJ105 L1: MURATA LQH3C100K24 D1, D2, D3, D4: MOTOROLA MBR0530 (408) 573-4150 (408) 573-4150 (408) 573-4150 (814) 237-1431 (800) 441-2447 1615/-1 TA05 U PACKAGE DESCRIPTIO S5 Package 5-Lead Plastic SOT-23 (Reference LTC DWG # 05-08-1633) (Reference LTC DWG # 05-08-1635) 2.80 – 3.10 (.110 – .118) (NOTE 3) .20 (.008) A A2 DATUM ‘A’ L NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 2.60 – 3.00 1.50 – 1.75 (.102 – .118) (.059 – .069) (NOTE 3) 1.90 (.074) REF .09 – .20 (.004 – .008) (NOTE 2) 3. DRAWING NOT TO SCALE 4. DIMENSIONS ARE INCLUSIVE OF PLATING 5. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 6. MOLD FLASH SHALL NOT EXCEED .254mm 7. PACKAGE EIAJ REFERENCE IS: SC-74A (EIAJ) FOR ORIGINAL JEDEL MO-193 FOR THIN A1 A SOT-23 (Original) .90 – 1.45 (.035 – .057) SOT-23 (ThinSOT) 1.00 MAX (.039 MAX) A1 .00 – .15 (.00 – .006) .01 – .10 (.0004 – .004) A2 .90 – 1.30 (.035 – .051) .80 – .90 (.031 – .035) L .35 – .55 (.014 – .021) .30 – .50 REF (.012 – .019 REF) PIN ONE .95 (.037) REF .25 – .50 (.010 – .020) (5PLCS, NOTE 2) S5 SOT-23 0401 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1307 Single-Cell Micropower 600kHz PWM DC/DC Converter 3.3V at 75mA from One Cell, MSOP Package LT1316 Burst ModeTM Operation DC/DC with Programmable Current Limit 1.5V Minimum, Precise Control of Peak Current Limit LT1317 2-Cell Micropower DC/DC with Low-Battery Detector 3.3V at 200mA from Two Cells, 600kHz Fixed Frequency LT1610 Single-Cell Micropower DC/DC Converter 3V at 30mA from 1V, 1.7MHz Fixed Frequency LT1611 1.4MHz Inverting Switching Regulator in 5-Lead ThinSOT – 5V at 150mA from 5V Input, Tiny ThinSOT Package LT1613 1.4MHz Switching Regulator in 5-Lead ThinSOT 5V at 200mA from 3.3V Input, Tiny ThinSOT Package LT1617 Micropower Inverting DC/DC Converter in 5-Lead ThinSOT –15V at 12mA from 2.5V Input, Tiny ThinSOT Package Burst Mode is a trademark of Linear Technology Corporation sn16151 16151fas 8 Linear Technology Corporation 16151fa LT/TP 0601 1.5K REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 1998