LT3460 1.3MHz Step-Up DC/DC Converter in SC70 and ThinSOT U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ 1.3MHz Switching Frequency High Output Voltage: Up to 36V 300mA Integrated Switch 12V at 70mA from 5V Input 5V at 60mA from 3.3V Input Wide Input Range: 2.5V to 16V Uses Small Surface Mount Components Low Shutdown Current: <1µA Low Profile (1mm) SC70 and SOT-23 (ThinSOTTM) Packages U APPLICATIO S ■ ■ ■ ■ ■ ■ The high voltage switch in the LT3460 is rated at 38V, making the device ideal for boost converters up to 36V. The LT3460 can generate 12V at up to 70mA from a 5V supply. The LT3460 is available in SC70 and SOT-23 packages. , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation Digital Cameras CCD Bias Supply XDSL Power Supply TFT-LCD Bias Supply Local 5V or 12V Supply Medical Diagnostic Equipment Battery Backup U ■ The LT®3460 is a general purpose step-up DC/DC converter. The LT3460 switches at 1.3MHz, allowing the use of tiny, low cost and low height capacitors and inductors. The constant frequency results in low, predictable output noise that is easy to filter. TYPICAL APPLICATIO Efficiency 90 5V to 12V, 70mA Step-Up DC/DC Converter 22µH VIN 5V 4.7µF VIN VOUT 12V 70mA SW 130k 22pF EFFICIENCY (%) 85 80 75 70 65 LT3460 OFF ON SHDN 60 FB GND 1µF 15k 0 20 40 60 LOAD CURRENT (mA) 80 3460 F01a Switching Waveforms 3460 F01 VSW 5V/DIV IL 100mA/DIV 0.2µs/DIV 3460 F01b 3460f 1 LT3460 U W W W ABSOLUTE AXI U RATI GS (Note 1) Input Voltage (VIN) .................................................. 16V SW Voltage .............................................................. 38V FB Voltage ................................................................. 5V SHDN Voltage .......................................................... 16V Operating Ambient Temperature Range (Note 2) .................. – 40°C to 85°C Maximum Junction Temperature .......................... 125°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C U W U PACKAGE/ORDER I FOR ATIO ORDER PART NUMBER TOP VIEW ORDER PART NUMBER TOP VIEW SW 1 5 VIN LT3460ES5 GND 2 FB 3 4 SHDN SW 1 6 VIN GND 2 5 GND FB 3 S5 PACKAGE 5-LEAD PLASTIC TSOT-23 S5 PART MARKING TJMAX = 125°C, θJA = 256°C/W IN FREE AIR θJA = 120°C ON BOARD OVER GROUND PLANE LTB1 LT3460ESC6 4 SHDN SC6 PART MARKING SC6 PACKAGE 6-LEAD PLASTIC SC70 LAAF TJMAX = 125°C, θJA = 400°C/W IN FREE AIR θJA = 270°C/W ON BOARD OVER GROUND PLANE 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 = 3V, VSHDN = 3V, unless otherwise noted. PARAMETER CONDITIONS MIN Minimum Operating Voltage TYP UNITS 2.5 V Maximum Operating Voltage Feedback Voltage ● Feedback Line Regulation MAX 1.235 1.225 2.5V < VIN < 16V FB Pin Bias Current V 1.275 1.280 V V 0.015 ● 5 Supply Current SHDN = 0V Switching Frequency 1.255 16 1.0 %/V 25 80 nA 2.0 0.1 3.0 0.5 mA µA 1.3 1.7 MHz Maximum Duty Cycle 85 90 Switch Current Limit 300 420 600 mA 320 450 mV 0.01 1 µA Switch VCESAT ISW = 250mA Switch Leakage Current VSW = 5V SHDN Voltage High 1.5 V SHDN Voltage Low SHDN Pin Bias Current Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. % 0.4 40 V µA Note 2: The LT3460E 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. 3460f 2 LT3460 U W TYPICAL PERFOR A CE CHARACTERISTICS Quiescent Current SHDN Pin Bias Current Switching Frequency 2.5 1.4 400 1.2 350 25°C 1.5 1.0 0.5 0 1.0 0.8 0.6 0.4 0.2 0 –50 15 10 5 SHDN = 16V 300 250 200 150 100 50 –25 VIN (V) 50 25 0 TEMPERATURE (°C) 3460 G01 0 –50 100 75 SHDN = 3V –25 50 25 0 TEMPERATURE (°C) 3460 G02 Feedback Bias Current 75 100 3460 G03 Feedback Voltage 30 1.260 25 1.255 20 VFB (V) FEEDBACK BIAS CURRENT (nA) 0 15 1.250 10 1.245 5 0 –50 –25 50 25 0 TEMPERATURE (°C) 75 1.240 –50 100 –25 50 25 0 TEMPERATURE (°C) 75 3460 G04 Current Limit vs Duty Cycle 400 350 450 400 IC = 250mA 350 300 250 IC = 200mA 200 150 100 IC = 100mA 300 250 200 150 100 50 0 –50 100 3460 G05 Switch Saturation Voltage (VCESAT) VCESAT (mV) IQ (mA) 100°C CURRENT LIMIT (mA) 2.0 SHDN PIN BIAS CURRENT (µA) SWITCHING FREQUENCY (MHz) –50°C 50 0 –25 50 25 0 TEMPERATURE (°C) 75 100 3460 G06 0 0.2 0.6 0.4 DUTY CYCLE 0.8 1.0 3460 G07 3460f 3 LT3460 U U U PI FU CTIO S (ThinSOT/SC70 Packages) SW (Pin 1/Pin 1): Switch Pin. Connect inductor/diode here. Minimize trace at this pin to reduce EMI. SHDN (Pin 4/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/Pins 2 and 5): Ground Pin. Tie directly to local ground plane. VIN (Pin 5/Pin 6): Input Supply Pin. Must be locally bypassed. FB (Pin 3/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). W BLOCK DIAGRA VIN (PIN 6 SC70 PACKAGE) 5 1.255V REFERENCE COMPARATOR + – A1 VOUT – A2 RC 3 FB R2 (EXTERNAL) SW R Q Q1 S + R1 (EXTERNAL) FB 1 DRIVER CC + ∑ 0.1Ω – SHUTDOWN RS (EXTERNAL) 4 SHDN RAMP GENERATOR CS (EXTERNAL) RS, CS OPTIONAL SOFT-START COMPONENTS 1.3MHz OSCILLATOR 2 GND (PINS 2 AND 5 SC70 PACKAGE) 3460 BD Figure 1. Block Diagram U OPERATIO The LT3460 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. 3460f 4 LT3460 U OPERATIO Feedback Loop Compensation is about 70kHz. The LT3460 has an internal feedback compensation network as shown in Figure 1 (RC and CC). However, because the small signal characteristics of a boost converter change with operation conditions, the internal compensation network cannot satisfy all applications. A properly designed external feed forward capacitor from VOUT to FB (CF in Figure 2) will correct the loop compensation for most applications. The feedback loop gain T(s) = K3 • GP(s) • GC(s). If it crosses over 0dB far before fZ, the phase margin will be small. Figure 3 is the Bode plot of the feedback loop gain measured from the converter shown in Figure 2 without the feedforward capacitor CF. The result agrees with the previous discussion: Phase margin of about 20° is insufficient. 60 VIN 5V 5 1 VIN SW R2 130k CF 22pF VOUT 12V 70mA LT3460 OFF ON 4 SHDN FB 3 GND 2 R1 15k C1: TAIYO YUDEN X5R JMK212BJ475KG C2: TAIYO YUDEN X5R EMK316BJ105 D1: CENTRAL SEMICONDUCTOR CMDSH2-3 L1: MURATA LQH32CN-220 OR EQUIVALENT C2 1µF 90 50 45 GAIN 40 0 30 –45 20 –90 PHASE 10 –135 0 –180 –10 –225 –20 –270 –30 –315 1 10 100 FREQUENCY (kHz) Figure 2. 5V to 12V Step-Up Converter The LT3460 uses peak current mode control. The current feedback makes the inductor very similar to a current source in the medium frequency range. The power stage transfer function in the medium frequency range can be approximated as: GP(s ) = K1 , s • C2 where C2 is the output capacitance, and K1 is a constant based on the operating point of the converter. In continuous current mode, K1 increases as the duty cycle decreases. The internal compensation network RC, CC can be approximated as follows in medium frequency range: GC(s ) = K2 • s • RC • CC + 1 s • CC The zero fZ = 1 2 • π • RC • CC –360 1000 –40 3460 F02 PHASE (DEG) C1 4.7µF D1 GAIN (dB) L1 22µH 3460 F03 Figure 3 In order to improve the phase margin, a feed-forward capacitor CF in Figure 2 can be used. Without the feed-forward capacitor, the transfer function from VOUT to FB is: FB R1 = VOUT R1 + R2 With the feed-forward capacitor CF, the transfer function becomes: FB R1 s • R2 • CF + 1 • = VOUT R1 + R2 s • R1 • R2 • C + 1 F R1 + R2 The feed-forward capacitor CF generates a zero and a pole. The zero always appears before the pole. The frequency distance between the zero and the pole is determined only by the ratio between VOUT and FB. To give maximum phase 3460f 5 LT3460 U OPERATIO margin, CF should be chosen so that the midpoint frequency between the zero and the pole is at the cross over frequency. With CF = 20pF, the feedback loop Bode plot is reshaped as shown in Figure 4. The phase margin is about 60°. 90 60 45 GAIN 40 0 30 –45 –90 20 PHASE 10 –135 0 –180 –10 –225 –20 –270 –30 –315 10 100 FREQUENCY (kHz) The high speed operation of the LT3460 demands careful attention to board layout. You will not get advertised performance with careless layout. Figure 5 shows the recommended component placement. 3460 F04 Figure 4. L1 D1 For most of the applications of LT3460, the output capacitor ESR zero is at very high frequency and can be ignored. If a low frequency ESR zero exists, for example, when a high-ESR Tantalum capacitor is used at the output, the phase margin may be enough even without a feed-forward capacitor. In these cases, the feed-forward capacitor should not be added because it may cause the feedback loop to not have enough attenuation at the switching frequency. Layout Hints –360 1000 –40 1 PHASE (DEG) GAIN (dB) 50 The feed-forward capacitor increases the gain at high frequency. The feedback loop therefore needs to have enough attenuation at the switching frequency to reject the switching noise. Additional internal compensation components have taken this into consideration. C1 L1 D1 C1 + + VOUT VIN VOUT VIN + + C2 C2 SHUTDOWN R2 GND SHUTDOWN R2 R1 CF GND (SOT-23 PACKAGE) R1 CF (SC70 PACKAGE) 3460 F05 Figure 5. Suggested Layout 3460f 6 LT3460 U TYPICAL APPLICATIO S Efficiency 5V to 12V Step-Up Converter 90 VIN 5V D1 5 C1 4.7µF VOUT 12V 70mA 1 VIN 130k SW 85 22pF EFFICIENCY (%) L1 22µH LT3460 SHDN 4 SHDN 3 FB C2 1µF 15k GND 2 C1: TAIYO YUDEN X5R JMK212BJ475 C2: TAIYO YUDEN X5R EMK212BJ105 D1: CENTRAL SEMICONDUCTOR CMDSH2-3 L1: MURATA LQH32CN-220 OR EQUIVALENT 80 75 70 65 60 3460 TA01 0 20 40 60 LOAD CURRENT (mA) 80 3460 TA01a Load Step Response VOUT 100mV/DIV 58mA ILOAD 34mA 100µs/DIV 3460 TA01b Input Current and Output Voltage 5V to 12V with Soft-Start Circuit L1 22µH VIN 5V C1 4.7µF D1 VOUT 12V 70mA CONTROL SIGNAL VIN 47k SW SHDN 47nF 130k FB GND C1: TAIYO YUDEN X5R JMK212BJ475 C2: TAIYO YUDEN X5R EMK212BJ105 D1: CENTRAL SEMICONDUCTOR CMDSH2-3 L1: MURATA LQH32CN-220 OR EQUIVALENT 22pF C2 1µF 16V LT3460 IIN 100mA/DIV 15k VO 5V/DIV CONTROL SIGNAL 2V/DIV 3460 TA02 500µs/DIV 3460 TA02b 3460f 7 LT3460 U TYPICAL APPLICATIO S 3.3V to 12V Step-Up Converter C1 4.7µF VIN D1 VOUT 12V 40mA 130k SW 22pF C2 1µF 16V LT3460 SHDN FB 80 EFFICIENCY (%) L1 22µH VIN 3.3V Efficiency 85 15k GND 75 70 65 60 C1: TAIYO YUDEN X5R JMK212BJ475 C2: TAIYO YUDEN X5R EMK212BJ105 D1: CENTRAL SEMICONDUCTOR CMDSH2-3 L1: MURATA LQH32CN-220 OR EQUIVALENT 3460 TA03 55 0 20 30 10 LOAD CURRENT (mA) 40 3460 TA03a Li-Ion to 5V Step-Up Converter D1 VOUT 5V 88 VIN = 4.2V 86 VIN SW 39.2k C2 4.7µF 6.3V LT3460 4.7µF SHDN FB GND 50pF 13k EFFICIENCY (%) + C1 90 L1 10µH VIN 2.7V TO 4.2V Efficiency 84 VIN = 3.6V 82 VIN = 3V 80 VIN = 2.7V 78 76 74 C1: TAIYO YUDEN X5R JMK212BJ475 C2: TAIYO YUDEN X5R JMK212BJ475 D1: PHILIPS PMEG2010 L1: MURATA LQH32CN-100 OR EQUIVALENT 3460 TA07 72 70 0 50 200 150 100 LOAD CURRENT (mA) 250 3460 TA07a 3460f 8 LT3460 U TYPICAL APPLICATIO S 12V to 36V Step-Up Converter L1 47µH VIN 12V C1 1µF 16V D1 Load Step Response VOUT 36V 4mA D2 VIN 278k SW C2 0.22µF 50V LT3460 SHDN VOUT 100mV/DIV 22pF FB 10k GND ILOAD C1: TAIYO YUDEN X5R EMK212BJ105 C2: TAIYO YUDEN X7R UMK212BJ224 D1, D2: CENTRAL SEMICONDUCTOR CMOD4448 L1: TAIYO YUDEN LB2012 4mA 2mA 3460 TA04 100µs/DIV 3460 TA04a 5V to 36V Step-Up Converter L1 47µH VIN 5V C1 1µF 6.3V D1 Load Step Response VOUT 36V 4mA D2 VIN SW 278k C2 0.22µF 50V LT3460 SHDN FB GND VOUT 100mV/DIV 22pF 10k ILOAD C1: TAIYO YUDEN X5R JMK107BJ105 C2: TAIYO YUDEN X7R UMK212BJ224 D1, D2: CENTRAL SEMICONDUCTOR CMOD4448 L1: TAIYO YUDEN LB2012 3460 TA05 4mA 2mA 100µs/DIV 3460 TA05a 3460f 9 LT3460 U PACKAGE DESCRIPTIO S5 Package 5-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1635) 0.62 MAX 0.95 REF 2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 3.85 MAX 2.62 REF 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 – 0.45 TYP 5 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 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 1.90 BSC S5 TSOT-23 0302 3460f 10 LT3460 U PACKAGE DESCRIPTIO SC6 Package 6-Lead Plastic SC70 (Reference LTC DWG # 05-08-1638) 0.47 MAX 0.65 REF 1.80 – 2.20 (NOTE 4) 1.16 REF 0.96 MIN 3.26 MAX 2.1 REF INDEX AREA (NOTE 6) 1.80 – 2.40 1.15 – 1.35 (NOTE 4) PIN 1 RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.65 BSC 0.15 – 0.30 6 PLCS (NOTE 3) 0.10 – 0.40 0.80 – 1.00 0.00 – 0.10 REF 1.00 MAX 0.10 – 0.30 0.10 – 0.18 (NOTE 3) SC6 SC70 0802 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. DETAILS OF THE PIN 1 INDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE INDEX AREA 7. EIAJ PACKAGE REFERENCE IS EIAJ SC-70 3460f 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 LT3460 U TYPICAL APPLICATIO S 5V to 5V SEPIC VIN 3V TO 10V C1 1µF VIN C3 0.22µF SW D1 VOUT 5V 50mA L2 22µH 30k 50pF LT3460 SHDN C2 1µF FB VIN = 6.5V 75 VIN = 4V EFFICIENCY (%) L1 22µH Efficiency 80 VIN = 5V 70 65 60 10k GND 55 C1, C2: TAIYO YUDEN X5R LMK107BJ105 C3: TAIYO YUDEN X7R LMK107BJ224 D1: ON SEMICONDUCTOR MBR0520 L1, L2: MURATA LQH32CN-220 OR EQUIVALENT 3460 TA06 50 0 100 50 LOAD CURRENT (mA) 150 3460 TA06a RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1613 550mA (ISW), 1.4MHz, High Efficiency Step-Up DC/DC Converter VIN: 0.9V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD <1µA, ThinSOT Package 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 = 20µA, ISD <1µA, 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 = 20µA, ISD <1µA, MS Package LT1945 Dual Output, Pos/Neg, 350mA (ISW), Constant Off-Time, High Efficiency Step-Up DC/DC Converter VIN: 1.2V to 15V, VOUT(MAX) = ±34V, IQ = 20µA, ISD <1µA, MS Package LT1961 1.5A (ISW), 1.25MHz, High Efficiency Step-Up DC/DC Converter VIN: 3V to 25V, VOUT(MAX) = 35V, IQ = 0.9mA, ISD <6µA, MS8E Package LTC3400/LTC3400B 600mA (ISW), 1.2MHz, Synchronous Step-Up DC/DC Converter VIN: 0.85V to 5V, VOUT(MAX) = 5V, IQ = 19µA/300µA, ISD <1µA, ThinSOT Package LTC3401/LTC3402 1A/2A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter VIN: 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38µA, ISD <1µA, MS Package LT3461/LT3461A 0.3A (ISW), 1.3MHz/3MHz, High Efficiency Step-Up DC/DC Converter with Integrated Schottky VIN: 2.5V to 16V, VOUT(MAX) = 38V, IQ = 2.8mA, ISD <1µA, SC70, ThinSOT Packages LT3464 0.08A (ISW), High Efficiency Step-Up DC/DC Converter with Integrated Schottky, Output Disconnect VIN: 2.3V to 10V, VOUT(MAX) = 34V, IQ = 25µA, ISD <1µA, ThinSOT Package 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) = 30V, IQ = 1.9mA, ISD <1µA, ThinSOT Package 3460f 12 Linear Technology Corporation LT/TP 0204 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2003