LT3489

FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ LT3489 2MHz Boost DC/DC Converter with 2.5A Switch and Soft-Start DESCRIPTIO The LT®3489 is a fixed frequency step-up DC/DC converter containing an internal 2.5A, 40V switch. The LT3489 is ideal for large TFT-LCD panel power supplies. The LT3489 switches at 2MHz, allowing the use of tiny, low profile inductors and low value ceramic capacitors. Loop compensation can be either internal or external, giving the user flexibility in setting loop compensation and allowing optimized transient response with low ESR ceramic output capacitors. Soft-start is controlled with an external capacitor, which determines the input current ramp rate during start-up. The 8-lead MS8E package and high switching frequency ensure a low profile overall solution less than 1.1mm high. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. 2.5A, 0.12Ω, 40V Internal Switch 2MHz Switching Frequency Integrated Soft-Start Function VIN Range: 2.6V to 16V Adjustable Output from VIN to 40V Low VCESAT Switch: 110mV at 1A (Typical) 8V at 610mA from a 3.3V Input Internal or External Loop Compensation Small 8-Lead MS8E APPLICATIO S ■ ■ ■ ■ TFT-LCD Bias Supplies GPS Receivers DSL Modems Local Power Supply TYPICAL APPLICATIO Low Profile, Triple Output TFT Supply (8V, –8V, 23V) VON 23V 10mA 0.1µF 0.1µF 0.1µF 90 85 80 EFFICIENCY (%) 75 70 65 60 VIN 3.3V VIN OFF ON SHDN SS 4.7µF 100nF 2.2µH AVDD 8V 610mA SW 28.7k + LT3489 FB GND 5.23k 37.4k 220pF 0.1µF 2µF VOFF –8V 20mA 20µF 2µF COMP VC 3489 TA01 U U U Efficiency 55 V LOAD = 10mA ON VOFF LOAD = 20mA 50 100 200 300 400 500 600 0 AVDD LOAD CURRENT (mA) 700 3489 TA01b 3489f 1 LT3489 ABSOLUTE (Note 1) AXI U RATI GS PACKAGE/ORDER I FOR ATIO TOP VIEW VC FB SHDN GND 1 2 3 4 8 7 6 5 SS COMP VIN SW VIN Voltage ................................................................16V SW Voltage ................................................ –0.4V to 40V FB, VC, COMP, SS Voltages .........................................6V SHDN Voltage ...........................................................16V Current Into FB Pin ................................................±1mA Maximum 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 MS8E PACKAGE 8-LEAD PLASTIC MSOP TJMAX = 125°C, θJA = 40°C/W, θJC = 10°C/W EXPOSED PAD (PIN 9) IS GND (MUST BE SOLDERED TO PCB) ORDER PART NUMBER LT3489EMS8E MS8E PART MARKING LTBYF Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS PARAMETER Minimum Operating Voltage Maximum Operating Voltage Feedback Voltage CONDITIONS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3V, VSHDN = VIN unless otherwise noted. (Note 2) MIN TYP 2.4 1.22 1.21 1.235 100 100 80 VSHDN = 2.5V, Not Switching VSHDN = 0V, VIN = 3V 2.6V ≤ VIN ≤ 16V ● ● MAX 2.6 16 1.26 1.26 250 UNITS V V V V nA μmhos V/V ● FB Pin Bias Current Error Amp Transconductance Error Amp Voltage Gain Quiescent Current Quiescent Current in Shutdown Reference Line Regulation Switching Frequency Maximum Switch Duty Cycle Switch Current Limit Switch VCESAT Switch Leakage Current SHDN Pin Current VFB = 1.25V (Note 3) ΔI = 10μA ● 2 0 0.01 1.8 85 2.5 2 90 3.5 0.23 0.01 100 20 2 0.3 1.5 10 4 1 0.05 2.2 5 1 (Note 4) ISW = 2A VSW = 5V VSHDN = 5V VSHDN = 1.4V VSHDN = 0V VSS = 0.5V ● SHDN Pin Threshold Soft-Start Charging Current 2 20 5 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 LT3489E is 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, characterization and correlation with statistical process controls. Note 3: Current flows out of the FB pin. Note 4: Current limit guaranteed by design and/or correlation to static test. Current limit is independent of duty cycle and is guaranteed by design. 3489f 2 U mA μA % MHz % A V μA μA μA μA V μA W U U WW W LT3489 TYPICAL PERFOR A CE CHARACTERISTICS Feedback Pin Voltage 1.27 1.26 FEEDBACK VOLTAGE (V) 1.25 1.24 1.23 1.22 1.21 –50 –25 OSCILLATOR FREQUENCY (MHz) 2.4 CURRENT LIMIT (A) 50 25 75 0 TEMPERATURE (˚C) Switch VCE(SAT) Voltage 600 500 QUIESCENT CURRENT (mA) 400 300 200 100 0 1 0.5 1.0 1.5 2.0 SWITCH CURRENT (A) –50°C 25°C 125°C 2.5 3489 G04 VCE(SAT) (mV) UW 100 3489 G01 TA = 25°C unless otherwise noted. Oscillator Frequency 4.0 3.5 2.2 3.0 2.5 2.0 1.5 1.0 0.5 125 1.6 –50 –25 75 0 25 50 TEMPERATURE (°C) 100 125 Current Limit 2.0 1.8 0 –50 –25 0 50 25 TEMPERATURE (°C) 75 100 3489 03 3489 G02 Quiescent Current 4.0 3.5 3.0 2.5 2.0 1.5 1.0 –50 –25 IL 1A/DIV VOUT 100mV/DIV AC COUPLED VSW 10V/DIV Switching Waveform for the Cover Page Circuit 50 25 75 0 TEMPERATURE (˚C) 100 125 VIN = 3.3V 200ns/DIV AVDD = 8V ILOAD, AVDD = 400mA VON = 23V, 10mA VOFF = –8V, 20mA 3489 G06 3489 G05 3489f 3 LT3489 PI FU CTIO S VC (Pin 1): Error Amplifier Output Pin. Tie external compensation network to this pin, or use the internal compensation network by shorting the VC pin to the COMP pin. FB (Pin 2): Feedback Pin. Reference voltage is 1.235V. Connect resistive divider tap here. Minimize the trace area at FB. Set VOUT according to VOUT = 1.235 • (1 + R1/R2). SHDN (Pin 3): Shutdown Pin. Tie to 2V or more to enable device. Ground to shut down. Do not float this pin. GND (Pin 4): Ground. Tie directly to local ground plane. SW (Pin 5): Switch Pin. This is the collector of the internal NPN power switch. Minimize the metal trace area connected to this pin to minimize EMI. VIN (Pin 6): Input Supply Pin. Must be locally bypassed. COMP (Pin 7): Internal Compensation Pin. Provides an internal compensation network. Tie directly to the VC pin for internal compensation. Tie to GND if not in use. SS (Pin 8): Soft-Start Pin. Place a soft-start capacitor here. Upon start-up, 10μA of current charges the capacitor to 1.8V. Use a larger capacitor for slower start-up. Leave floating if not in use. Exposed Pad (Pin 9): Ground. Must be soldered to PCB. BLOCK DIAGRA VIN 6 SS 8 VOUT R1 (EXTERNAL) FB R2 (EXTERNAL) 1.235V REFERENCE + + – A1 Σ – RAMP GENERATOR 4 2MHz OSCILLATOR SHUTDOWN 3 SHDN 2 FB Figure 1. Block Diagram 4 + – W U U U VC 1 COMP 7 100k 125pF SW 5 COMPARATOR DRIVER A2 R S Q Q1 + 0.01Ω 9 GND 3489 F01 GND 3489f LT3489 OPERATIO The LT3489 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. Please refer to Figure 1 for the following description of the part’s operation. At the start of the oscillator cycle, the SR latch is set, turning on the power switch, Q1. The switch current flows through the internal current sense resistor generating a voltage. This voltage 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 (VC pin) is set by the error amplifier (gm) and is simply an amplified version of the difference between the feedback voltage and the reference voltage of 1.235V. In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. U A soft-start function is provided to enable a clean start-up for the LT3489. When the part is brought out of shutdown, 10µA of current is sourced out of the SS pin. By connecting an external capacitor to the SS pin, the rate of voltage rise on the pin can be set. Typical values for the soft-start capacitor range from 10nF to 200nF. The SS pin indirectly limits the rate of rise on the VC pin, which in turn limits the peak switch current. Current limit is not shown in Figure 1. The switch current is constantly monitored and not allowed to exceed the nominal value of 2.5A. If the switch current reaches 2.5A, the SR latch is reset regardless of the output of comparator A2. This current limit helps protect the power switch as well as the external components connected to the LT3489. 3489f 5 LT3489 APPLICATIO S I FOR ATIO Inductor Selection Several inductors that work well with the LT3489 are listed in Table 1. This table is not exclusive; there are many other manufacturers and inductors that can be used. Consult each manufacturer for more detailed information and for their entire selection of related parts, as many different sizes and shapes are available. Ferrite core inductors should be used to obtain the best efficiency, as core losses at 2MHz are much lower for ferrite cores than for the cheaper powdered-iron ones. Choose an inductor that can handle at least 2.5A without saturating, and ensure that the inductor has a low DCR (copper wire resistance) to minimize I2R power losses. A 2.2μH to 5μH inductor will be the best choice for most LT3489 designs. Note that in some applications, the current handling requirements of the inductor can be lower, such as in the SEPIC topology where each inductor only carries one-half of the total switch current. The inductors shown in Table 1 were chosen for small size. For better efficiency, use similar valued inductors with a larger volume. Table 1. Recommended Inductors PART SD25-2R2 SD25-3R3 SD25-4R7 A916CY-2R7M A916CY-3R3M A916CY-4R7M LQH55DN2R2M03 LQH55DN3R3M03 LQH55DN4R7M03 L (μH) 2.2 3.3 4.7 2.7 3.3 4.7 2.2 3.3 4.7 TYPICAL DCR (mΩ) 31 38 47 18.3 21.4 26.3 29 36 41 SIZE L × W × H (mm) 5.45 × 5.45 × 2.7 VENDOR CooperBussmann (888) 414-2645 www.cooperet.com Toko www.toko.com Murata (770) 436-1300 www.murata.com Table 2. Ceramic Capacitor Manufacturers Taiyo Yuden AVX Murata (408) 573-4150 www.t-yuden.com (843) 448-9411 www.avxcorp.com (770) 436-1300 www.murata.com 6 U Capacitor Selection Low ESR (equivalent series resistance) capacitors should be used at the output to minimize the output ripple voltage. Multilayer ceramic capacitors are an excellent choice, as they have an extremely low ESR and are available in very small packages. X5R or X7R dielectrics are preferred, as these materials retain the capacitance over wide voltage and temperature ranges. A 4.7µF to 20µF output capacitor is sufficient for most applications, but systems with very low output currents may need only a 1µF or 2.2µF output capacitor. Solid tantalum 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 LT3489. A 2.2μF to 4.7μF input capacitor is sufficient for most applications. Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for detailed information on their entire selection of ceramic parts. 6 × 6 × 3.5 5.7 × 5 × 4.7 3489f W U U LT3489 APPLICATIO S I FOR ATIO Diode Selection Schottky diodes, with their low forward voltage drop and fast switching speed, are ideal for LT3489 applications. Table 3 lists several Schottky diodes that work well with the LT3489. The diode’s average current rating must exceed the average output current. The diode’s maximum reverse voltage must exceed the output voltage. The diode conducts current only when the power switch is turned off (typically less than 50% duty cycle), so a 3A diode is sufficient for most designs. The companies below also offer Schottky diodes with high voltage and current ratings. Table 3. Suggested Diodes MANUFACTURER MAXIMUM PART NUMBER CURRENT (A) UPS340 UPS315 B220 B230 B240 B320 B330 B340 SBM340 3 3 2 2 2 3 3 3 3 MAXIMUM REVERSE VOLTAGE (V) 40 15 20 30 40 20 30 40 40 MANUFACTURER Microsemi www.microsemi.com Diodes, Inc www.diodes.com Frequency Compensation To compensate the feedback loop of the LT3489, a series resistor-capacitor network should be connected from the COMP pin to GND. For most applications, a capacitor in the range of 220pF to 680pF will suffice. A good starting value for the compensation capacitor, CC, is 470pF. The compensation resistor, RC, is usually in the range of 20k to 100k. A thorough analysis of the switching regulator control loop is not within the scope of this data sheet and will not be presented here, but values of 20k and 680pF will be a good choice for many designs. R1 U Setting Output Voltage To set the output voltage, select the values of R1 and R2 (see Figure 1) according to the following equation: ⎛V ⎞ R1= R2 • ⎜ OUT − 1⎟ ⎝ 1.235V ⎠ A good range for R2 is from 5k to 30k. Board Layout The high speed operation of the LT3489 demands careful attention to board layout. For high-current switching regulators like the LT3489, the board layout must have good thermal performance. Vias located underneath the part should be connected to an internal ground plane to improve heat transfer from the LT3489 to the PCB board. You will not get advertised performance with careless layout. Thermal and noise consideration must be taken into account. Figure 2 shows the recommended component placement for a boost converter. GROUND PLANE CSS C1 CC RC 1 2 R2 SHUTDOWN LT3489 3 4 MULTIPLE VIAs GND C2 VOUT 6 5 8 7 L1 W U U + VIN 3489 F02 Figure 2. Recommended Component Placement for Boost Converter. Note Direct High Current Paths Using Wide PC Traces. Minimize Trace Area at Pin 1 (VC) and Pin 2 (FB). Use Multiple Vias to Tie Pin 4 Copper to Ground Plane. Use Vias at One Location Only to Avoid Introducing Switching Currents Into the Ground Plane 3489f 7 LT3489 TYPICAL APPLICATIO S 8V Output Boost Converter VIN 3.3V TO 5V 3 8 L1 2.2µH 6 VIN SHDN SS LT3489 FB GND 4 R2 5.23k 2 5 SW D1 VOUT 650mA, VIN = 3.3V 1.1A, VIN = 5V R1 28.7k C2 20µF OFF ON + C1 4.7µF CSS 100nF C1: AVX 08056D475KAT C2: 2 × 10µF, TAIYO YUDEN LMK3168BJ106ML D1: DIODES INC. DFLS220L L1: COOPER BUSSMANN SD25-2R2 *EXPOSED PAD MUST ALSO BE GROUNDED Efficiency 90 85 80 EFFICIENCY (%) 75 70 65 60 55 50 VIN = 3.3V VIN = 5V 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 LOAD CURRENT (A) 3489 TA09 8 U 7 COMP VC 1 RC 35.7k CC 330pF 3489 TA02 Transient Response VOUT 100mV/DIV AC COUPLED IL1 1A/DIV 400mA IOUT 200mA VIN = 3.3V 50µs/DIV 3489 G10 3489f LT3489 TYPICAL APPLICATIO S 12V Output Boost Converter VIN 3.3V TO 5V 3 1 L1 3.3µH 6 VIN SHDN LT3489 VC SS CSS 100nF 8 7 FB COMP GND 4 2 R2 9.76k 5 SW D1 VOUT 12V 625mA, VIN = 5V 410mA, VIN = 3.3V R1 84.5k C2 10µF Efficiency 90 85 80 EFFICIENCY (%) 75 70 65 60 55 50 45 40 0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) VIN = 3.3V VIN = 5V 0.6 0.7 300mA IOUT 100mA IL1 1A/DIV VOUT 500mV/DIV AC COUPLED U OFF ON C1 4.7µF RC 16.5k CC 680pF C1: Taiyo Yuden JMK212BJ475MG, 4.7µF, 6.3V C2: Taiyo Yuden GMK316BJ106ML, 10µF, 35V D1: Diodes, Inc. DFLS220 L1: Toko A916CY-3R3M (Type D63CB) 3489 TA03 Transient Response VIN = 3.3V 50µs/DIV 3489 TA06 3489 TA05 3489f 9 LT3489 TYPICAL APPLICATIO U D2 D3 D4 D5 VON 23V 10mA C5 0.1µF L1 2.2µH 6 VIN SHDN SS LT3489 FB GND* 4 R3 5.23k 2 5 SW D1 10mA R2 28.7k C2 20µF C4 2µF C6 0.1µF C7 0.1µF AVDD 8V 610mA OFF ON 3 8 C1 4.7µF CSS 100nF 7 COMP VC 1 37.4k 220pF C1 TO C8: X5R OR X7R C1: AVX 08056D475KAT C2: 2 × 10µF, TAIYO YUDEN LMK316BJ106ML C3: 2 × 10µF, 10V C4: 2 × 1µF, AVX08053D105KAT C5, C6, C7: 0.1µF, 10V C8: 0.1µF, 16V D1: DIODES INC. DFLS220L D2 TO D7: ZETEX BAT54S OR EQUIVALENT L1: COOPER BUSSMANN SD25-2R2 * EXPOSED PAD MUST ALSO BE GROUNDED C8 0.1µF D7 C3 2µF D6 VOFF –8V 20mA 3489 TA04 VIN 3.3V + Effciency 90 85 80 EFFICIENCY (%) 75 70 65 60 55 V LOAD = 10mA ON VOFF LOAD = 20mA 50 100 200 300 400 500 600 0 AVDD LOAD CURRENT (mA) 400mA ILOAD 200mA IL1 1A/DIV AVDD 100mV/DIV AC COUPLED Transient Response AVDD 5V/DIV VON 20V/DIV VOFF 5V/DIV Start-Up Waveforms IIN 0.5A/DIV 5µs/DIV 3489 TA07 5ms/DIV 3489 TA08 700 3489 TA01b 3489f 10 LT3489 PACKAGE DESCRIPTIO U MS8E Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1662) BOTTOM VIEW OF EXPOSED PAD OPTION 1 2.06 ± 0.102 (.081 ± .004) 1.83 ± 0.102 (.072 ± .004) 2.794 ± 0.102 (.110 ± .004) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 2.083 ± 0.102 3.20 – 3.45 (.082 ± .004) (.126 – .136) 8 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.42 ± 0.038 (.0165 ± .0015) TYP 0.65 (.0256) BSC 8 7 65 0.52 (.0205) REF RECOMMENDED SOLDER PAD LAYOUT DETAIL “A” 0° – 6° TYP 1 0.53 ± 0.152 (.021 ± .006) DETAIL “A” 0.18 (.007) SEATING PLANE 0.22 – 0.38 (.009 – .015) TYP 0.127 ± 0.076 (.005 ± .003) MSOP (MS8E) 0603 0.254 (.010) GAUGE PLANE 4.90 ± 0.152 (.193 ± .006) 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 23 4 0.86 (.034) REF 1.10 (.043) MAX NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 0.65 (.0256) BSC 3489f 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 LT3489 RELATED PARTS PART NUMBER LT1613 LT1615/LT1615-1 LT1618 LT1930/LT1930A LT1935 LT1946/LT1946A LT1961 LT3436 LT3464 LT3467/LT3467A LT3477 LT3479 DESCRIPTION 550mA (ISW), 1.4MHz, High Efficiency Step-Up DC/DC Converter 300mA/80mA (ISW), High Efficiency Step-Up DC/DC Converters 1.5A (ISW), 1.25MHz, High Efficiency Step-Up DC/DC Converter 1A (ISW), 1.2MHz/2.2MHz, High Efficiency Step-Up DC/DC Converters 2A (ISW), 1.2MHz/2.7MHz, High Efficiency Step-Up DC/DC Converter 1.5A (ISW), 1.2MHz, High Efficiency Step-Up DC/DC Converters 1.5A (ISW), 1.25MHz, High Efficiency Step-Up DC/DC Converter 3A (ISW), 1MHz, 34V Step-Up DC/DC Converter COMMENTS VIN: 0.9V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD =