LT3461/LT3461A 1.3MHz/3MHz Step-Up DC/DC Converters with Integrated Schottky in ThinSOT FEATURES DESCRIPTION Integrated Schottky Rectifier nn Fixed Frequency 1.3MHz/3MHz Operation nn High Output Voltage: Up to 38V nn Low V CESAT Switch: 260mV at 250mA nn 12V at 70mA from 5V Input nn 5V at 115mA from 3.3V Input nn Wide Input Range: 2.5V to 16V nn Uses Small Surface Mount Components nn Low Shutdown Current: <1A nn Soft-Start nn Low Profile (1mm) SOT-23 (ThinSOTTM) Package The LT(R)3461/LT3461A are general purpose fixed frequency current mode step-up DC/DC converters. Both devices feature an integrated Schottky and a low VCESAT switch allowing a small converter footprint and lower parts cost. The LT3461 switches at 1.3MHz while the LT3461A switches at 3MHz. These high switching frequencies enable the use of tiny, low cost and low height capacitors and inductors. The constant switching frequency results in predictable output noise that is easy to filter, and the inductor based topology ensures an input free from switching noise typically present with charge pump solutions. The high voltage switch in the LT3461/LT3461A is rated at 40V making the device ideal for boost converters up to 38V. nn APPLICATIONS The LT3461/LT3461A are available in a low profile (1mm) SOT-23 package. Digital Cameras nn CCD Bias Supply nn XDSL Power Supply nn TFT-LCD Bias Supply nn Local 5V or 12V Supply nn Medical Diagnostic Equipment nn Battery Backup nn L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and ThinSOT is a trademark of Linear Technology Corporation. TYPICAL APPLICATION 5V to 12V, 70mA Step-Up DC/DC Converter Efficiency 85 L1 10H C1 1F OFF ON 1 SW 5 VIN VOUT LT3461A 4 3 SHDN FB GND 2 80 6 261k 30.1k 15pF VOUT 12V 70mA C2 1F 3461 TA01a EFFICIENCY (%) VIN 5V VIN = 5V 75 VIN = 3.3V 70 65 60 0 20 60 40 LOAD CURRENT (mA) 80 3461 TAO1b 3461afa For more information www.linear.com/LT3461 1 LT3461/LT3461A ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW Input Voltage (VIN).....................................................16V VOUT, SW Voltage.......................................................40V FB Voltage....................................................................5V SHDN Voltage............................................................16V Operating Ambient Temperature Range (Note 2).....................-40C to 85C Maximum Junction Temperature........................... 125C Storage Temperature Range................... -65C to 150C Lead Temperature (Soldering, 10 sec).................... 300C SW 1 GND 2 FB 3 6 VIN 5 VOUT 4 SHDN S6 PACKAGE 6-LEAD PLASTIC TSOT-23 TJMAX = 125C, JA = 150C ON BOARD OVER GROUND PLANE, JC = 120C/W ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT3461AES6#PBF LT3461AES6#TRPBF LTAHG 8-Lead Plastic TSOT-23 -40C to 85C LT3461ES6#PBF LT3461ES6#TRPBF LTAEB 8-Lead Plastic TSOT-23 -40C to 85C Consult LTC Marketing for parts specified with wider operating temperature ranges. 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/. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. 3461afa 2 For more information www.linear.com/LT3461 LT3461/LT3461A ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C, VIN = 3V, VSHDN = 3V, unless otherwise noted. PARAMETER CONDITIONS MIN Minimum Operating Voltage TYP Feedback Voltage l Feedback Line Regulation 1.235 1.225 1.255 0.005 FB Pin Bias Current l FB = 1.3V, Not Switching SHDN = 0V UNITS V Maximum Operating Voltage Supply Current MAX 2.5 16 V 1.275 1.280 V V %/V 40 100 nA 2.8 0.1 3.6 0.5 mA A Switching Frequency (LT3461A) l 2.1 3.0 3.9 MHz Switching Frequency (LT3461) l 1.0 1.3 1.7 MHz Maximum Duty Cycle (LT3461A) l 82 Maximum Duty Cycle (LT3461) l Switch Current Limit % 92 300 % 420 600 mA 350 mV Switch VCESAT ISW = 250mA 260 Switch Leakage Current VSW = 5V 0.01 1 A Schottky Forward Voltage ISCHOTTKY = 250mA 800 1100 mV Schottky Reverse Leakage VOUT - SW = 40V 0.03 4 A 0.4 V 50 A SHDN Voltage High 1.5 V SHDN Voltage Low SHDN Pin Bias Current 35 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. Note 2: The LT3461E/LT3461AE is guaranteed to meet specifications from 0C to 70C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls. 3461afa For more information www.linear.com/LT3461 3 LT3461/LT3461A TYPICAL PERFORMANCE CHARACTERISTICS Oscillator Frequency (LT3461) Current Limit 1.6 480 FB Pin Voltage 1.28 TA = 25C 1.27 1.4 1.3 1.2 360 FB VOLTAGE (V) CURRENT LIMIT (mA) FREQUENCY (MHz) 1.5 240 1.25 1.24 120 1.1 1.23 1.0 -40 -20 40 20 60 0 TEMPERATURE (C) 80 0 10 100 20 30 40 50 60 70 DUTY CYCLE (%) 80 Oscillator Frequency (LT3461A) 480 420 3.0 2.7 2.4 TA = 25C 360 300 240 180 120 0 1.3 100 TA = 25C 280 60 80 100 80 SHDN Pin Current 320 SHDN PIN CURRENT (A) CURRENT LIMIT (mA) 3.6 3.3 40 20 60 0 TEMPERATURE (C) 3461a G03 Current Limit in Soft-Start Mode 3.9 2.1 -60 -40 -20 0 20 40 60 TEMPERATURE (C) 1.22 -40 -20 90 3461a G02 3461a G01 FREQUENCY (MHz) 1.26 240 200 160 120 80 40 1.5 1.7 2.1 1.9 SHDN PIN VOLTAGE (V) 2.3 0 4 0 8 12 3461a G06 3461a G05 3461a G04 Switching Waveform Circuit of Figure 4 16 SHDN PIN VOLTAGE (V) Load Transient Response Circuit of Figure 4 ILOAD VSW 5V/DIV 70mA 35mA VOUT 100mV/DIV VOUT 50mV/DIV ILOAD = 60mA 0.2s/DIV 3461a G08 50s/DIV 3461a G09 3461afa 4 For more information www.linear.com/LT3461 LT3461/LT3461A PIN FUNCTIONS SW (Pin 1): Switch Pin. Connect inductor here. Minimize trace at this pin to reduce EMI. SHDN (Pin 4): Shutdown Pin. Tie to 1.5V or higher to enable device; 0.4V or less to disable device. Also functions as soft-start. Use RC filter (47k, 47nF typ) as shown in Figure 1. GND (Pin 2): Ground Pin. Tie directly to local ground plane. VOUT (Pin 5): Output Pin. Connect to resistor divider. Put capacitor close to pin and close to GND plane. FB (Pin 3): Feedback Pin. Reference voltage is 1.255V. Connect resistor divider tap here. Minimize trace area at FB. Set VOUT according to VOUT = 1.255V (1 + R1/R2). VIN (Pin 6): Input Supply Pin. Must be locally bypassed. BLOCK DIAGRAM 1.255V REFERENCE VIN 6 - R1 (EXTERNAL) FB 3 FB CC R2 (EXTERNAL) R A2 RC SW DRIVER - A1 VOUT 1 COMPARATOR + + S Q 5 VOUT Q1 + 0.1 - SHUTDOWN RS (EXTERNAL) 4 SHDN CS (EXTERNAL) RS, CS OPTIONAL SOFT-START COMPONENTS RAMP GENERATOR 3MHz* OSCILLATOR GND 2 *LT3461 IS 1.3MHz 3461a F01 Figure 1. Block Diagram OPERATION Layout Hints The high speed operation of the LT3461/LT3461A demands careful attention to board layout. You will not get advertised performance with careless layout. Figure 2 shows the recommended component placement. C1 + GND L1 VIN R2 + The LT3461/LT3461A uses a constant frequency, current mode control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the block diagram in Figure 1. At the start of each oscillator cycle, the SR latch is set, which turns on the power switch Q1. A voltage proportional to the switch current is added to a stabilizing ramp and the resulting sum is fed into the positive terminal of the PWM comparator A2. When this voltage exceeds the level at the negative input of A2, the SR latch is reset turning off the power switch. The level at the negative input of A2 is set by the error amplifier A1, and is simply an amplified version of the difference between the feedback voltage and the reference voltage of 1.255V. In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier's output increases, more current is delivered to the output; if it decreases, less current is delivered. R1 C2 VOUT SHUTDOWN C3 3461a F02 Figure 2. Suggested Layout For more information www.linear.com/LT3461 3461afa 5 LT3461/LT3461A APPLICATIONS INFORMATION Inrush Current 160 VIN = 8V VIN = 12V 120 IOUT (mA) The LT3461 has a built-in Schottky diode. When supply voltage is applied to the VIN pin, the voltage difference between VIN and VOUT generates inrush current flowing from input through the inductor and the Schottky diode to charge the output capacitor. The maximum nonrepetitive surge current the Schottky diode in the LT3461 can sustain is 1.5A. The selection of inductor and capacitor value should ensure the peak of the inrush current to be below 1.5A. In addition, turn-on of the LT3461 should be delayed until the inrush current is less than the maximum current limit. The peak inrush current can be calculated as follows: VIN = 5V VIN >15V 80 40 0 6 14 22 30 38 VOUT (V) 3461 F03a Figure 3a. LT3461 Operating Region V - 0.6 * IP = IN exp - L L - 12 - 12 2 C C 160 VIN = 5V where L is the inductance, r is the resistance of the inductor and C is the output capacitance. Table 3 gives inrush peak currents for some component selections. Table 3. Inrush Peak Current VIN (V) L (H) C (F) IP (A) 5 4.7 1 1.1 5 10 1 0.9 Thermal Considerations Significant power dissipation can occur on the LT3461 and LT3461A, particularly at high input voltage. Device load, voltage drops in the power path components, and switching losses are the major contributors. It is important to measure device power dissipation in an application to ensure that the LT3461 does not exceed the absolute maximum operating junction temperature of 125C over the operating ambient temperature range. Generally, for supply voltages below 5V the integrated current limit function provides adequate protection for nonfault conditions. For supply voltages above 5V, Figures 3a and 3b show the recommended operating region of the LT3461 and LT3461A, respectively. These graphs are based on 250mW on-chip dissipation. Improvement of these numbers can be expected if the LT3461 is supplied from a separate low voltage rail. IOUT (mA) 120 VIN = 8V VIN = 12V VIN >15V 80 40 0 6 14 22 30 38 VOUT (V) 3461 F03b Figure 3b. LT3461A Operating Region Switching Frequency The key difference between the LT3461 and LT3461A is the faster switching frequency of the LT3461A. At 3MHz, the LT3461A switches at twice the rate of the LT3461. The higher switching frequency of the LT3461A allows physically smaller inductors and capacitors to be used in a given application, but with a slight decrease in efficiency and maximum output current when compared to the LT3461. Generally if efficiency and maximum output current are crucial, or a high output voltage is being generated, the LT3461 should be used. If application size and cost are more important, the LT3461A will be the better choice. 3461afa 6 For more information www.linear.com/LT3461 LT3461/LT3461A APPLICATIONS INFORMATION Inductor Selection The inductors used with the LT3461/LT3461A should havea saturation current rating of 0.3A or greater. If the device is used in an application where the input supply will be hot-plugged, then the saturation current rating should be equal to or greater than the peak inrush current. For the LT3461, an inductor value between 10H and 47H, depending upon output voltage, will usually be the best choice for most designs. For the LT3461A, inductor values between 4.7H and 15H inductor will suffice for most applications. For best loop stability results, the inductor value selected should provide a ripple current of 70mA or more. For a given VIN and VOUT the inductor value to use with LT3461A is estimated by the formula: L (in microhenries) = D * VIN * VOUT *1sec 1A * 1V VOUT +1V - VIN VOUT +1V Use twice this value for the LT3461. where D = they have a low ESR and maintain capacitance over wide voltage and temperature range. A 2.2F output capacitor is sufficient for most applications using the LT3461, while a 1F capacitor is sufficient for most applications using the LT3461A. High output voltages typically require less capacitance for loop stability. Always use a capacitor with sufficient voltage rating. Either ceramic or solid tantalum capacitors may be used for the input decoupling capacitor, which should be placed as close as possible to the LT3461/LT3461A. A 1F capacitor is sufficient for most applications. Phase Lead Capacitor A small value capacitor can be added across resistor R1 between the output and the FB pin to reduce output perturbation due to a load step and to improve transient response. This phase lead capacitor introduces a pole-zero pair to the feedback that boosts phase margin near the cross-over frequency. The following formula is useful to estimate the capacitor value needed: CPL = Capacitor Selection Low ESR capacitors should be used at the output to minimize the output voltage ripple. Multilayer ceramic capacitors using X5R/X7R dielectrics are preferred as 500k *1pF R2 For an application running 50A in the feedback divider, capacitor values from 10pF to 22pF work well. TYPICAL APPLICATIONS L1 10H VIN 5V C1 1F CONTROL SIGNAL 47k 47nF 1 SW 5 VIN VOUT LT3461A 4 3 SHDN FB GND 2 Input Current and Output Voltage 6 C1, C2: TAIYO YUDEN EMK212BJ105 L1: MURATA LQH32CN100K53 R1 261k R2 30.1k 15pF VOUT 12V 70mA C2 1F 3461a TA02a CONTROL SIGNAL 5V/DIV IIN 50mV/DIV VOUT 5V/DIV 1ms/DIV 3461 TA02b Figure 4. 5V to 12V with Soft-Start Circuit (LT3461A) 3461afa For more information www.linear.com/LT3461 7 LT3461/LT3461A TYPICAL APPLICATIONS 3.3V to 5V Step-Up Converter Efficiency 80 3.3V to 5V Step-Up Converter (LT3461A) L1 4.7H 75 1 SW 5 VIN VOUT LT3461A 4 3 SHDN FB GND 2 6 C1 1F OFF ON R1 45.3k 15pF EFFICIENCY (%) VIN 3.3V VOUT 5V 115mA C2 1F R2 15k C1, C2: TAIYO YUDEN X7R LMK212BJ105 L1: MURATA LQH32CN4R7M33 OR EQUIVALENT 70 65 3461a TA03a 60 0 30 60 90 LOAD CURRENT (mA) 120 3461a TA03b PACKAGE DESCRIPTION Please refer to http://www.linear.com/product/LT3461#packaging for the most recent package drawings. 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 2.80 BSC 1.4 MIN 3.85 MAX 2.62 REF 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) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 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 3461afa 8 For more information www.linear.com/LT3461 LT3461/LT3461A REVISION HISTORY (Revision history begins at Rev B) REV DATE DESCRIPTION A 01/16 Modified inrush current IP equation. PAGE NUMBER 6 3461afa 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. For more information www.linear.com/LT3461 9 LT3461/LT3461A TYPICAL APPLICATION Low Profile (1mm) 3.3V to 15V Step-Up Converter 3.3V to 15V Efficiency 75 L1 10H 1 SW 5 VIN VOUT LT3461A 4 3 SHDN FB GND 2 70 VOUT 15V 25mA 6 C1 1F OFF ON 332k 22pF EFFICIENCY (%) VIN 3.3V C2 2.2F 30.1k C1: TAIYO YUDEN LMK107BJ105KA C2: TAIYO YUDEN EMK316BJ225KD (X5R) L1: MURATA LQH2MCN100K02 65 60 55 3461a TA04a 50 0 5 5V to 36V Step-Up Converter (LT3461) OFF ON 30 3461a TA04b 5V to 36V Efficiency 75 280k VOUT 36V 18mA 22pF C2 0.47F 50V 10k C1: TAIYO YUDEN X7R LMK212BJ105 C2: MURATA GRM42-6X7R474K50 L1: MURATA LQH32CN470 70 EFFICIENCY (%) C1 1F 1 SW 6 5 VIN VOUT LT3461 4 3 SHDN FB GND 2 25 80 L1 47H VIN 5V 10 15 20 LOAD CURRENT (mA) 65 60 55 3461 TA05a 50 0 2 4 6 8 10 12 14 16 18 LOAD CURRENT (mA) 3.3V to 5V Dual Output Converter C3 1F L1 4.7H VIN 3.3V 1 SW 5 VIN VOUT LT3461A 4 3 SHDN FB GND 2 3461 TA05b VOUT 5V 100mA 6 C1 1F OFF ON 45.3k 15pF C2 1F 15k D1 C1, C2, C3, C4: TAIYO YUDEN JMK107BJ105 D1, D2: PHILIPS PMEG2005EB L1: MURATA LQH2MCN4R7M02 D2 C4 1F 10 -5V 15mA 3461 TA06 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1615/LT1615-1 300mA/80mA (ISW) Constant Off-Time, High Efficiency Step-Up DC/DC Converter VIN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 20A, ISD <1A, ThinSOT Package LT1944/LT1944-1 Dual Output 350mA/100mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter VIN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 20A, ISD <1A, MS Package LTC3400/LTC3400B 600mA (ISW), 1.2MHz, Synchronous Step-Up DC/DC Converter VIN: 0.85V to 5V, VOUT(MAX) = 5V, IQ = 19A/300A, ISD <1A, ThinSOT Package LT3460 0.32A (ISW), 1.3MHz, High Efficiency Step-Up DC/DC Converter VIN: 2.5V to 16V, VOUT(MAX) = 36V, IQ = 2mA, ISD <1A, SC70, ThinSOT Packages LT3465/LT3465A Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED Boost Regulator with Integrated Schottky Diode VIN: 2.7V to 16V, VOUT(MAX) = 34V, IQ = 1.9mA, ISD <1A, ThinSOT Package 3461afa 10 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LT3461 (408) 432-1900 FAX: (408) 434-0507 www.linear.com/LT3461 LT 0116 REV A * PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2003