LM3355 Regulated 50mA Buck-Boost Switched Capacitor DC/DC Converter General Description Features The LM3355 is a CMOS switched capacitor DC/DC converter that produces a regulated output voltage by automatically stepping up (boost) or stepping down (buck) the input voltage. It accepts an input voltage between 2.5V and 5.5V. The LM3355 is available with a standard output voltage of 4.1V (ideal for white LED applications). If other output voltage options between 1.8V and 4.1V are desired for other applications, please contact your National Semiconductor representative. The LM3355’s proprietary buck-boost architecture enables up to 50 mA of load current at an average efficiency greater than 75%. Typical operating current is only 375 µA and the typical shutdown current is only 2.3 µA. The LM3355 is available in a 10-pin MSOP package. This package has a maximum height of only 1.1 mm. The high efficiency of the LM3355, low operating and shutdown currents, small package size, and the small size of the overall solution make this device ideal for battery powered, portable, and hand-held applications. See the LM3352 for up to 200mA of output current. n Regulated VOUT with ± 3% accuracy n Standard output voltage of 4.1V n Custom output voltages available from 1.8V to 4.1V in 100 mV increments n 2.5V to 5.5V input voltage n Up to 50 mA output current n > 75% average efficiency n Uses few, low-cost external components n Very small solution size n 375 µA typical operating current n 2.3 µA typical shutdown current n 1 MHz switching frequency (typical) n Architecture and control methods provide high load current and good efficiency n MSOP-10 package n Over-temperature protection Applications n White LED display backlights n 1-cell Lilon battery-operated equipment including PDAs, hand-held PCs, cellular phones n Flat panel displays n Hand-held instruments n NiCd, NiMH, or alkaline battery powered systems Typical Operating Circuit DS200219-1 © 2001 National Semiconductor Corporation DS200219 www.national.com LM3355 Regulated 50 mA Buck-Boost Switched Capacitor DC/DC Converter December 2001 LM3355 Connection Diagram DS200219-2 Top View MSOP-10 Pin Package See NS Package Number MUB10A Ordering Information NSC Package Drawing Supplied As LM3355MMX-4.1 Order Number Package Type MSOP-10 MUB10A 3.5k Units, Tape and Reel LM3355MM-4.1 MSOP-10 MUB10A 1k Units, Tape and Reel Pin Description www.national.com Pin Number Name 1 VIN Input Supply Voltage Function 2 C1− Negative Terminal for C1 3 C1+ Positive Terminal for C1 4 GND Ground 5 GND Ground 6 CFIL Filter Capacitor, a 1µF capacitor is recommended. 7 SD Shutdown, active low 8 VOUT Regulated Output Voltage 9 C2− Negative Terminal for C2 10 C2+ Positive Terminal for C2 2 ESD Rating (Note 3) Human Body Model Machine Model If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. All Pins Power Dissipation (TA = 25˚C) (Note 2) TJMAX (Note 2) θJA (Note 2) Storage Temperature Lead Temperature (Soldering, 5 sec.) 1.5 kV 100V Operating Ratings −0.5V to 5.6V Input Voltage (VIN) Output Voltage (VOUT) Ambient Temperature (TA) (Note 2) Junction Temperature (T J) (Note 2) Internally Limited 150˚C 250˚C/W −65˚C to +150˚C 260˚C 2.5V to 5.5V 1.8V to 4.1V −40˚C to +85˚C −40˚C to +125˚C Electrical Characteristics Limits in standard typeface are for TA = 25˚C, and limits in boldface type apply over the full operating temperature range of −40˚C ≤ TA ≤ 85˚C. Unless otherwise specified: C1 = C2 = 0.33 µF; CIN = 10 µF; COUT = 10 µF; CFIL = 1 µF; VIN = 3.5V. Parameter Conditions Min (Note 5) Typ (Note 4) Max (Note 5) Units LM3355-4.1 Output Voltage (V OUT) Efficiency Output Voltage Ripple (Peak-to-Peak) VIN = 3.5V; I 4.038 4.1 4.162 2.6V < VIN < 5.5V; 1 mA < ILOAD < 50 mA 3.977/3.936 4.1 4.223/4.264 2.5V < VIN < 5.5V; 1 mA < ILOAD < 40 mA 3.977/3.936 4.1 4.223/4.264 LOAD = 50 mA ILOAD = 10 mA 80 ILOAD= 50 mA 75 ILOAD = 50 mA C OUT = 10 µF ceramic 75 V % mVP-P LM3355-ALL OUTPUT VOLTAGE VERSIONS Operating Quiescent Current Measured at Pin VIN; I LOAD = 0A (Note 6) 375 475 µA Shutdown Quiescent Current SD Pin at 0V (Note 7) 2.3 5 µA 1.40 MHz 0.2 VIN V Switching Frequency 0.60 SD Input Threshold Low 2.5V < VIN < 5.5V SD Input Threshold High 2.5V < VIN < 5.5V SD Input Current Measured at SD Pin; SD Pin = VIN = 5.5V 1 0.8 VIN V 0.3 µA Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur. Operating Ratings are conditions for which the device is intended to be functional, but device parameter specifications may not be guaranteed. For guaranteed specifications and test conditions, see “Electrical Characteristics”. Note 2: As long as TA ≤ +85˚C, all electrical characteristics hold true and the junction temperature should remain below +125˚C. Note 3: The Human Body Model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. The Machine Model is a 200 pF capacitor discharged directly into each pin. Note 4: Typical numbers are at 25˚C and represent the most likely norm. Note 5: All limits guaranteed at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits are 100% tested or guaranteed through statistical analysis. All limits at temperature extremes are guaranteed by correlation using standard Statistical Quality Control methods (SQC). All limits are used to calculate Average Outgoing Quality Level (AOQL). Note 6: The VOUT pin is forced to 200 mV above the typical VOUT. This is to insure that the internal switches are off. Note 7: The output capacitor COUT is fully discharged before measurement. 3 www.national.com LM3355 Absolute Maximum Ratings (Note 1) LM3355 Typical Performance Characteristics Unless otherwise specified TA = 25˚C. VOUT vs. VIN VOUT vs. VIN DS200219-4 Efficiency vs. VIN DS200219-5 Load Transient Response DS200219-14 DS200219-20 Operating Quiescent Current vs. VIN Switching Frequency vs. VIN DS200219-23 DS200219-24 www.national.com 4 Unless otherwise specified TA = 25˚C. (Continued) Maximum VOUT Ripple vs. COUT Maximum VOUT Ripple vs. COUT LM3355 Typical Performance Characteristics DS200219-30 DS200219-32 Applications Information DS200219-3 FIGURE 1. Block Diagram gain signal is sent to the phase generator which then sends the appropriate timing and configuration signals to the switch array. This dual loop provides regulation over a wide range of loads efficiently. Since efficiency is automatically optimized, the curves for VOUT vs. VIN and Efficiency vs. VIN in the Typical Performance Characteristics section exhibit small variations. The reason is that as input voltage or output load changes, the digital control loops are making decisions on how to optimize efficiency. As the switch array is reconfigured, small variations in output voltage and efficiency result. In all cases where these small variations are observed, the part is operating correctly; minimizing output voltage changes and optimizing efficiency. Operating Principle The LM3355 is designed to provide a step-up/step-down voltage regulation in battery powered systems. It combines switched capacitor circuitry, reference, comparator, and shutdown logic in a single 10-pin MSOP package. The LM3355 can provide a regulated voltage between 1.8V and 4.1V from an input voltage between 2.5V and 5.5V. It can supply a load current up to 50 mA. As shown in Figure 1, the LM3355 employs two feedback loops to provide regulation in the most efficient manner possible. The first loop is from VOUT through the comparator COMP, the AND gate G1, the phase generator, and the switch array. The comparator’s output is high when VOUT is less than the reference VREF. Regulation is provided by gating the clock to the switch array. In this manner, charge is transferred to the output only when needed. The second loop controls the gain configuration of the switch array. This loop consists of the comparator, the digital control block, the phase generator, and the switch array. The digital control block computes the most efficient gain from a set of five gains based on inputs from the A/D and the comparator. The Charge Pump Capacitor Selection A 0.33 µF ceramic capacitor is suggested for C1 and C2. To ensure proper operation over temperature variations, an X7R dielectric material is recommended. 5 www.national.com LM3355 choice for low ripple, high frequency applications. However, the temperature stability of the ceramics is bad, except for the X7R and X5R dielectric types. High capacitance values ( > 1 µF) are achievable from companies such as Taiyo-yuden which are suitable for use with regulators. Ceramics are taller and larger than the tantalums of the same capacitance value. Filter Capacitor Selection a) CAPACITOR TECHNOLOGIES The three major technologies of capacitors that can be used as filter capacitors for LM3355 are: i) tantalum, ii) ceramic and iii) polymer electrolytic technologies. i) Tantalum Tantalum capacitors are widely used in switching regulators. Tantalum capacitors have the highest CV rating of any technology; as a result, high values of capacitance can be obtained in relatively small package sizes. It is also possible to obtain high value tantalum capacitors in very low profile ( < 1.2 mm) packages. This makes the tantalums attractive for low-profile, small size applications. Tantalums also possess very good temperature stability; i.e., the change in the capacitance value, and impedance over temperature is relatively small. However, the tantalum capacitors have relatively high ESR values which can lead to higher voltage ripple and their frequency stability (variation over frequency) is not very good, especially at high frequencies ( > 1 MHz). iii) Polymer Electrolytic Polymer electrolytic is a third suitable technology. Polymer capacitors provide some of the best features of both the ceramic and the tantalum technologies. They provide very low ESR values while still achieving high capacitance values. However, their ESR is still higher than the ceramics, and their capacitance value is lower than the tantalums of the same size. Polymers offer good frequency stability (comparable to ceramics) and good temperature stability (comparable to tantalums). The Aluminum Polymer Electrolytics offered by Cornell-Dubilier and Panasonic, and the POSCAPs offered by Sanyo fall under this category. Table 1 compares the features of the three capacitor technologies. ii) Ceramic Ceramic capacitors have the lowest ESR of the three technologies and their frequency stability is exceptionally good. These characteristics make the ceramics an attractive TABLE 1. Comparison of Capacitor Technologies Ceramic Tantalum Polymer Electrolytic ESR Lowest High Low Relative Height Low for Small Values ( < 10 µF); Taller for Higher Values Lowest Low Relative Footprint Large Small Largest Temperature Stability X7R/X5R-Acceptable Good Good Frequency Stability Good Acceptable Good VOUT Ripple Magnitude @ < 50 mA Low High Low VOUT Ripple Magnitude @ > 100 mA Low Slightly Higher Low dv/dt of VOUT Ripple @ All Loads Lowest High Low ii) Input Capacitor (CIN) b) CAPACITOR SELECTION The input capacitor CIN directly affects the magnitude of the input ripple voltage, and to a lesser degree the VOUT ripple. A higher value CIN will give a lower VIN ripple. To optimize low input and output ripple as well as size a 10 µF polymer electrolytic or ceramic, or 15 µF tantalum capacitor is recommended. This will ensure low input ripple at 50 mA load current. If lower currents will be used or higher input ripple can be tolerated then a smaller capacitor may be used to reduce the overall size of the circuit. The lower ESR ceramics and polymer electrolytics achieve a lower VIN ripple than the higher ESR tantalums of the same value. Tantalums make a good choice for small size, very low profile applications. The ceramics and polymer electrolytics are a good choice for low ripple, low noise applications where size is less of a concern. The 10 µF polymer electrolytics are physically much larger than the 15 µF tantalums and 10 µF ceramics. i) Output Capacitor (COUT) The output capacitor COUT directly affects the magnitude of the output ripple voltage so COUT should be carefully selected. The graphs titled VOUT Ripple vs. COUT in the Typical Performance Characteristics section show how the ripple voltage magnitude is affected by the COUT value and the capacitor technology. These graphs are taken at the gain at which worst case ripple is observed. In general, the higher the value of COUT, the lower the output ripple magnitude. At lighter loads, the low ESR ceramics offer a much lower VOUT ripple than the higher ESR tantalums of the same value. At higher loads, the ceramics offer a slightly lower VOUT ripple magnitude than the tantalums of the same value. However, the dv/dt of the VOUT ripple with the ceramics and polymer electrolytics is much lower than the tantalums under all load conditions. The tantalums are suggested for very low profile, small size applications. The ceramics and polymer electrolytics are a good choice for low ripple, low noise applications where size is less of a concern. www.national.com 6 Of the different capacitor technologies, a sample of vendors that have been verified as suitable for use with the LM3355 are shown in Table 2. (Continued) iii) CFIL A 1 µF, X7R ceramic capacitor should be connected to pin CFIL. This capacitor provides the filtering needed for the internal supply rail of the LM3355. TABLE 2. Capacitor Vendor Information Manufacturer Ceramic Tel Fax Taiyo-yuden (408) 573-4150 (408) 573-4159 www.t-yuden.com Website AVX (803) 448-9411 (803) 448-1943 www.avxcorp.com Sprague/Vishay (207) 324-4140 (207) 324-7223 www.vishay.com Nichicon (847) 843-7500 (847) 843-2798 www.nichicon.com Cornell-Dubilier (ESRD) (508) 996-8561 (508) 996-3830 www.cornell-dubilier.com Sanyo (POSCAP) (619) 661-6322 (619) 661-1055 www.sanyovideo.com Tantalum Polymer Electrolytic pump action once the junction temperature exceeds the thermal trip point, and re-enables the charge pump when the junction temperature falls back to a safe operating point. Thermal Protection During output short circuit conditions, the LM3355 will draw high currents causing a rise in the junction temperature. On-chip thermal protection circuitry disables the charge Typical Application Circuits DS200219-33 FIGURE 2. Basic Buck/Boost Regulator DS200219-15 FIGURE 3. Low Output Noise and Ripple Buck/Boost Regulator 7 www.national.com LM3355 Filter Capacitor Selection LM3355 capacitors as close to the IC as possible and to keep the traces between the capacitors and the IC short and direct. Use of a ground plane is recommended. Layout Considerations Due to the 1 MHz typical switching frequency of the LM3355, careful board layout is a must. It is important to place the www.national.com 8 inches (millimeters) unless otherwise noted MSOP-10 Pin Package (MM) For Ordering, Refer to Ordering Information Table NS Package Number MUB10A LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. 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Tel: 81-3-5639-7560 Fax: 81-3-5639-7507 National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. LM3355 Regulated 50 mA Buck-Boost Switched Capacitor DC/DC Converter Physical Dimensions