LTC3427EDC

LTC3427 500mA, 1.25MHz Synchronous Step-Up DC/DC Converter in 2mm × 2mm DFN Package FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO High Efficiency: Up to 94% 3.3V at 200mA from Two Alkaline Cells 5V at 200mA from a Single Li-Ion Cell Inrush Current Limiting and Soft-Start Output Disconnect in Shutdown 1.8V to 5V VIN Range 1.8V to 5.25V VOUT Range 1.25MHz Fixed Frequency, Low Noise PWM Internal Synchronous Rectifier Logic Controlled Shutdown ( VOUT PMOS LDO MODE 90 1.23 –45 –30 –15 0 15 30 45 60 TEMPERATURE (°C) 75 90 40 1.5 2.5 3.5 VIN (V) 4.5 3427 G08 3427 G06 3427 G07 SW Pin Anti-Ringing Operation INDUCTOR CURRENT 50mA/DIV SW 2V/DIV 3427 G10 VIN = 1.8V VOUT = 3.3V COUT = 4.7µF L = 4.7µH 0 15 30 45 60 TEMPERATURE (°C) 75 200ns/DIV 90 3427 G09 VIN Supply Current (No Load) 0.45 TA = 25°C VIN = VOUT = VFB 0.40 0.35 0.30 1.5 2.5 3.5 VIN (V) 4.5 5.5 3427 G12 3427 G11 3427fa LTC3427 PI FU CTIO S SW (Pin 1): Switch Pin for the Inductor Connection. Minimize trace length between SW and the inductor. For discontinuous inductor current, an internal 200Ω impedance is connected from SW to VIN to eliminate high frequency ringing, reducing EMI radiation. GND (Pin 2): Signal and Power Ground. Provide a short, direct PCB path between GND and the (–) side of the input and output capacitor(s). VIN (Pin 3): Input Supply Voltage. Connect VIN to the input supply and decouple with a 2.2µF or larger ceramic capacitor as close to VIN as possible. SHDN (Pin 4): Shutdown Input. Less than 350mV on SHDN shuts down the LTC3427. Placing 1V or more on SHDN enables the LTC3427. FB (Pin 5): Feedback Input to the Error Amplifier. Connect resistor divider tap to this pin. Referring to the Block Diagram, VOUT can be adjusted from 1.8V to 5.25V by: BLOCK DIAGRA VIN 1.8V TO 5V + CIN 2.2µF SLOPE COMPENSATION 7 EXPOSED PAD –+– W U U U ⎛ R1⎞ VOUT = 1.24V • ⎜ 1+ ⎟ ⎝ R2 ⎠ VOUT (Pin 6): Output Voltage Sense Input and Drain of the Internal Synchronous Rectifier MOSFET. Driver bias is derived from VOUT. PCB trace length from VOUT to the output filter capacitor(s) should be as short and wide as possible. Exposed Pad (Pin 7): Ground for the LTC3427. This pin must be soldered to the PCB ground plane for electrical connection and rated thermal performance. L1 4.7µH OPTIONAL 4 SHDN 3 VIN VIN 1 SW BULK CONTROL SIGNALS ANTIRING VOUT 6 VOUT 1.8V TO 5.25V SHUTDOWN AND VBIAS SHDN PWM LOGIC AND DRIVERS CURRENT SENSE + IZERO COMP – 1.24V PWM COMP REFERENCE 1V GAIN ERROR AMPLIFIER R1 THERMAL SHUTDOWN + – START-UP SOFT-START FB 5 R2 COUT 4.7µF ILIM REF Σ + + 1.24V OSCILLATOR GND 2 3427 BD 3427fa 5 LTC3427 OPERATIO Shutdown LOW NOISE FIXED FREQUENCY OPERATION The LTC3427 is shut down by pulling the SHDN pin below 0.35V, and activated by pulling the SHDN pin above 1V. Note that SHDN can be driven above VIN or VOUT as long as it is limited to less than the absolute maximum rating. Soft-Start The LTC3427 provides soft-start by ramping the peak inductor current from zero to its peak value of 500mA. The soft-start time is typically 2ms. A soft-start cycle is reinitiated in the event of a commanded shutdown or a thermal shutdown. Oscillator The frequency of operation is set by an internal oscillator to 1.25MHz for the LTC3427. Error Amplifier The error amplifier is a transconductance type with its positive input internally connected to the 1.24V reference and the negative input connected to FB. Internal clamps limit the minimum and maximum error amplifier output voltage for improved large-signal transient response. Power converter control loop compensation is provided internally by the error amplifier. A voltage divider from VOUT to ground programs the output voltage via FB from 1.8V to 5.25V. ⎛ R1⎞ VOUT = 1.24V • ⎜ 1+ ⎟ ⎝ R2 ⎠ The error amplifier also provides a soft-start feature internal to the device. Current Sensing Lossless current sensing converts the peak current signal of the N-channel MOSFET switch into a voltage that is summed with the internal slope compensation. The summed signal is compared to the error amplifier output to provide a peak current control command for the PWM. Peak switch current is limited to 500mA minimum, independent 6 U (Refer to Block Diagram) of input or output voltage. The current signal is blanked for approximately 25ns to enhance noise rejection. Current Limit The current limit circuitry shuts off the internal N-channel MOSFET switch when the current limit threshold is reached. The current limit comparator delay to output is typically 40ns. Zero Current Comparator The zero current comparator monitors the inductor current to the output and shuts off the synchronous rectifier once this current reduces to approximately 20mA. Anti-Ringing Control The anti-ringing control connects a resistor across the inductor to damp the ringing on the SW pin in discontinuous conduction mode. The LCSW ringing (L = Inductor, CSW = capacitance on the SW pin) is low energy, but can cause EMI radiation. Output Disconnect and Inrush Limiting The LTC3427 provides true output disconnect by eliminating body diode conduction of the internal P-channel MOSFET rectifier. This allows VOUT to go to zero volts during shutdown without drawing any current from the input source. It also provides inrush current limiting at turn-on, minimizing surge currents seen by the input supply. Note that to obtain the advantages of output disconnect, there must not be any external Schottky diode connected between SW and VOUT. Thermal Shutdown If the die temperature reaches approximately 145 °C, the part will go into thermal shutdown. All switches will be turned off. The device will be enabled and initiate a softstart sequence when the die temperature drops by approximately 10°C. Note: Due to the high frequency operation of the LTC3427, board layout is extremely critical to minimize transients due to stray inductance. Keep the output filter capacitor as close as possible to the VOUT pin and use very low ESR/ ESL ceramic capacitors tied to a good ground plane. 3427fa LTC3427 APPLICATIO S I FOR ATIO SW 1 GND 2 + VIN VIN 3 Figure 1. Recommended Component Placement for a Single Layer Board. Traces Carrying High Current are Direct (GND, SW, VIN, VOUT). Trace Area at FB is Kept Low. Lead Length to Battery Should be Kept Short. VIN and VOUT Ceramic Capacitors Should be as Close to the LTC3427 as Possible. A Multilayer Board with a Separate Ground Plane is Ideal, but not Absolutely Necessary COMPONENT SELECTION Inductor Selection The LTC3427 can utilize small surface mount and chip inductors due to its fast 1.25MHz switching frequency. A minimum inductance value of 3.3µH is necessary for 3.6V and lower voltage applications and a 4.7µH for output voltages greater than 3.6V. Larger values of inductance will allow greater output current capability by reducing the inductor ripple current. Increasing the inductance above 10µH will increase size while providing little improvement in output current capability. The approximate output current capability of the LTC3427 vs Inductance value is given below in Equation 1 and illustrated graphically in Figure 2. V •D ⎞ ⎛ IOUT(MAX ) = n • ⎜ IP – IN ⎟ • (1 – D) ⎝ f • L • 2⎠ where: n = estimated efficiency IP = peak current limit value (0.5A min) VIN = input (battery) voltage D = steady-state duty ratio = (VOUT – VIN)/VOUT f = switching frequency (1.25MHz typical) L = inductance value U LTC3427 6 VOUT 5 FB MINIMIZE TRACE ON FB 4 SHDN MULTIPLE VIAS TO GROUND PLANE 3427 F01 W UU The inductor current ripple is typically set for 20% to 40% of the maximum inductor current (IP). High frequency ferrite core inductor materials reduce frequency dependent power losses compared to cheaper powdered iron types, improving efficiency. The inductor should have low ESR (series resistance of the windings) to reduce the I2R power losses, and must be able to handle the peak inductor current without saturating. Molded chokes and some chip inductors usually do not have enough core to support the peak inductor currents of greater than 500mA seen on the LTC3427. To minimize radiated noise, use a toroid, pot core or shielded bobbin inductor. See Table 1 for suggested suppliers. Output and Input Capacitor Selection Low ESR (equivalent series resistance) capacitors should be used to minimize the output voltage ripple. Multilayer ceramic capacitors are an excellent choice as they have extremely low ESR and are available in small footprints. A 2.2µF to 10µF output capacitor is sufficient for most applications. Larger values up to 22µF may be used to obtain extremely low output voltage ripple and improve transient response. An additional phase lead capacitor may be required with output capacitors larger than 10µF to maintain acceptable phase margin. X5R and X7R dielectric materials are preferred for their ability to maintain capacitance over wide voltage and temperature ranges. 3427fa (1) 7 LTC3427 APPLICATIO S I FOR ATIO Table 1. Inductor Vendor Information SUPPLIER Murata Sumida Coilcraft CoEv Magnetics TDK TOKO Wurth 0.280 0.260 0.240 1.8V TO 3V 3.1V TO 5V 1.8V TO 3.3V PHONE USA: (814) 237-1431 (800) 831-9172 USA: (847) 956-0666 Japan: 81-3-3607-5111 (847) 639-6400 (800) 227-7040 (847) 803-6100 (847) 297-0070 (201) 785-8800 OUTPUT CURRENT (A) 0.220 0.200 0.180 0.160 0.140 0.120 0.100 3 5 7 9 11 13 15 17 19 21 23 INDUCTANCE (µH) 3427 F02 1.8V TO 3.6V 1.8V TO 5V Figure 2. Maximum Output Current vs Inductance Based on 90% Efficiency Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the battery. It follows that ceramic capacitors are also a good choice for input decoupling and should be located as close as possible to the device. A 2.2µF input capacitor is sufficient for virtually any application. Larger values may be used without limitations. Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers directly for detailed information on their entire selection of ceramic capacitors. 8 U FAX USA: (814) 238-0490 USA: (847) 956-0702 Japan: 81-3-3607-5144 (847) 639-1469 (650) 361-2508 (847) 803-6296 (847) 669-7864 (201) 785-8810 WEBSITE www.murata.com www.sumida.com www.coilcraft.com www.circuitprotection.com/magnetics.asp www.component.tdk.com www.toko.com www.we-online.com W UU Table 2. Capacitor Vendor Information SUPPLIER PHONE AVX Sanyo TDK Murata (803) 448-9411 (619) 661-6322 (847) 803-6100 USA: (814) 237-1431 (800) 831-9172 (408) 573-4150 FAX (803) 448-1943 (619) 661-1055 (847) 803-629 USA: (814) 238-0490 (408) 573-4159 WEBSITE www.avxcorp.com www.sanyovideo.com www.component. tdk.com www.murata.com Taiyo Yuden www.t-yuden.com Thermal Considerations To deliver the power that the LTC3427 is capable of, it is imperative that a good thermal path be provided to dissipate the heat generated within the package. This can be accomplished by taking advantage of the large thermal pad on the underside of the LTC3427. It is recommended that multiple vias in the printed circuit board be used to conduct heat away from the LTC3427 and into the copper plane with as much area as possible. In the event that the junction temperature gets too high, the LTC3427 will go into thermal shutdown and all switching will stop until the internal temperature drops at which point a soft-start cycle will be initiated. 3427fa LTC3427 APPLICATIO S I FOR ATIO VIN > VOUT Operation The LTC3427 will maintain voltage regulation when the input voltage is above the output voltage. This is achieved by terminating the switching of the synchronous P-channel MOSFET and applying VIN statically on its gate. This will ensure the volt • seconds across the inductor reverse during the time current is flowing to the output. Since this mode will dissipate more power in the LTC3427, the maximum output current is limited in order to maintain an acceptable junction temperature and is given by: IOUT(MAX ) = 125 – TA 85 • ⎡( VIN + 1.5) – VOUT ⎤ ⎣ ⎦ where TA = ambient temperature. For example at VIN = 4.5V, VOUT = 3.3V, and TA = 85°C, the maximum output current is 145mA. U Short-Circuit Protection The LTC3427 output disconnect feature allows output short circuit while maintaining a maximum internally set current limit. However, the LTC3427 also incorporates internal features such as current limit foldback and thermal shutdown for protection from an excessive overload or short circuit. During a prolonged short circuit the current limit folds back to a typical value of approximately 400mA should VOUT drop below 950mV. This 400mA current limit remains in effect until VOUT exceeds approximately 1V, at which time the nominally internally set current limit is restored. 3427fa W UU 9 LTC3427 TYPICAL APPLICATIO S VIN 1.8V TO 3.2V 2-CELL ALKALINE L1 4.7µH + CIN 2.2µF VIN LTC3427 OFF ON SHDN VOUT 1000k GND FB 604k SW EFFICIENCY (%) CIN: TAIYO YUDEN X5R JMK212BJ225MD COUT: TAIYO YUDEN X5R JMK212BJ475MD L1: TDK RLF7030T-4R7M3R4 Figure 3. 2-Cell Alkaline to 3.3V Synchronous Boost Converter VIN 1.8V TO 3.2V 2-CELL ALKALINE + CIN 2.2µF VIN LTC3427 OFF ON SHDN VOUT 1000k GND FB 332k SW VOUT 5V 150mA COUT 4.7µF EFFICIENCY (%) CIN: TAIYO YUDEN X5R JMK212BJ225MD COUT: TAIYO YUDEN X5R JMK212BJ475MD L1: TDK RLF7030T-4R7M3R4 Figure 4. 2-Cell Alkaline to 5V Synchronous Boost Converter with Output Disconnect Li-Ion to 5V Synchronous Boost Converter VIN 3.1V TO 4.2V Li-Ion L1 4.7µH 100 95 90 + VIN LTC3427 OFF ON SHDN SW VOUT 5V 250mA COUT 4.7µF 332k EFFICIENCY (%) CIN 2.2µF CIN: TAIYO YUDEN X5R JMK212BJ225MD COUT: TAIYO YUDEN X5R JMK212BJ475MD L1: TDK RLF7030T-4R7M3R4 GND 10 U 2-Cell to 3.3V Efficiency 100 95 90 VOUT 3.3V 200mA COUT 4.7µF VIN = 3.1V VIN = 2.4V VIN = 1.8V 85 80 75 70 65 60 3427 F03a 55 50 1 10 100 LOAD CURRENT (mA) 1000 3427 G01 L1 4.7µH 2-Cell to 5V Efficiency 100 95 90 85 80 75 70 65 60 3427 F04a VIN = 3.2V VIN = 2.4V VIN = 1.8V 55 50 1 10 100 LOAD CURRENT (mA) 1000 3427 G03 Li-Ion to 5V Efficiency VIN = 4.2V VIN = 3.6V 85 80 75 70 65 60 55 VIN = 3.1V VOUT 1000k FB 3427 TA02a 50 1 10 100 LOAD CURRENT (mA) 1000 3427 G02 3427fa LTC3427 PACKAGE DESCRIPTIO 2.50 ± 0.05 1.15 ± 0.05 0.61 ± 0.05 (2 SIDES) PACKAGE OUTLINE RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP 0.56 ± 0.05 (2 SIDES) 2.00 ± 0.10 (4 SIDES) PIN 1 CHAMFER OF EXPOSED PAD 3 0.200 REF 0.75 ± 0.05 1 (DC6) DFN 1103 PIN 1 BAR TOP MARK (SEE NOTE 6) 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. U DC Package 6-Lead Plastic DFN (2mm × 2mm) (Reference LTC DWG # 05-08-1703) 0.675 ± 0.05 0.25 ± 0.05 0.50 BSC 1.42 ± 0.05 (2 SIDES) 0.38 ± 0.05 4 6 0.25 ± 0.05 0.50 BSC 1.37 ± 0.05 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WCCD-2) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 3427fa 11 LTC3427 RELATED PARTS PART NUMBER LT®1613 LT1615 LT1618 LT1930/LT1930A LTC3400/LTC3400B LTC3401 LTC3402 LTC3421 LTC3422 LTC3423/LTC3424 LTC3426 LTC3428 LTC3429 LTC3458 LTC3458L LTC3459 LTC3525-3.3 LTC3525-5 DESCRIPTION 800mA ISW, 1.4MHz, Step-Up DC/DC Converter 350mA ISW, Micropower, Step-Up DC/DC Converter 1.5A ISW, 1.4MHz, Constant Current/Constant Voltage Step-Up DC/DC Converter 1A ISW, 1.2MHz/2.2MHZ, Step-Up DC/DC Converters 600mA ISW, 1.2MHz, Synchronous Step-Up DC/DC Converters 1A ISW, 3MHz, Synchronous Step-Up DC/DC Converter 2A ISW, 3MHz, Synchronous Step-Up DC/DC Converter 3A ISW, 3MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect 1.5A ISW, 3MHz Synchronous Step-Up DC/DC Converter with Output Disconnect 1A/2A ISW, 3MHz, Synchronous Step-Up DC/DC Converter 2A ISW, 1.2MHz, Step-Up DC/DC Converter 500mA ISW, 1.25MHz/2.5MHz, Synchronous Step-Up DC/DC Converters with Output Disconnect 600mA ISW, 500kHz, Synchronous Step-Up DC/DC Converter with Output Disconnect and Soft-Start 1.4A ISW, 1.5MHz, Synchronous Step-Up DC/DC Converter/Output Disconnect/Burst Mode Operation 1.7A ISW, 1.5MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect, Automatic Burst Mode® Operation 70mA ISW, 10V Micropower Synchronous Boost Converter/Output Disconnect/Burst Mode Operation 400mA Micropower Synchronous Step-Up DC/DC Converter with Output Disconnect COMMENTS VIN: 1.1V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD < 1µA, 5-Lead SOT-23 Package VIN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 20µA, ISD < 1µA, ThinSOTTM Package VIN: 1.6V to 18V, VOUT(MAX) = 35V, IQ = 1.8mA, ISD < 1µA, DFN, MSOP Packages VIN: 2.6V to 16V, VOUT(MAX) = 34V, IQ = 4.2mA/5.5mA, ISD < 1µA, ThinSOT Package 92% Efficiency VIN: 0.85V to 5V, VOUT(MAX) = 5V, IQ = 19µA/300µA, ISD < 1µA, ThinSOT Package 97% Efficiency VIN: 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38µA, ISD < 1µA, 10-Lead MS Package 97% Efficiency VIN: 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38µA, ISD < 1µA, 10-Lead MS Package 95% Efficiency VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12µA, ISD < 1µA, QFN24 Package 95% Efficiency VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 25µA, ISD < 1µA, 3mm × 3mm DFN Package 95% Efficiency VIN: 0.5V to 5.5V, VOUT(MAX) = 5.5V, IQ = 38µA, ISD < 1µA, 10-Lead MS Package 92% Efficiency VIN: 1.6V to 4.3V, VOUT(MAX) = 5V, ISD < 1µA, SOT-23 Package 92% Efficiency VIN: 1.8V to 5V, VOUT(MAX) = 5.25V, ISD < 1µA, 2mm × 2mm DFN Package 96% Efficiency VIN: 0.5V to 4.4V, VOUT(MAX) = 5V, IQ = 20µA/300µA, ISD < 1µA, ThinSOT Package 93% Efficiency VIN: 1.5V to 6V, VOUT(MAX) = 7.5V, IQ = 15µA, ISD < 1µA, DFN12 Package 94% Efficiency VOUT(MAX) = 6V, IQ = 12µA, DFN12 Package VIN: 1.5V to 5.5V, VOUT(MAX) = 10V, IQ = 10µA, ISD < 1µA, ThinSOT Package 95% Efficiency VIN: 1V to 4.5V, VOUT(MAX) = 3.3V or 5V, IQ = 7µA, ISD < 1µA, SC-70 Package ThinSOT is a trademark of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. 3427fa 12 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● LT 0406 REV A • PRINTED IN THE USA www.linear.com © LINEAR TECHNOLOGY CORPORATION 2005