LM3354MMX-3.7

LM3354-3.7 Regulated 90mA Buck-Boost Switched Capacitor DC/DC Converter November 2002 LM3354-3.7 Regulated 90mA Buck-Boost Switched Capacitor DC/DC Converter General Description The LM3354 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 LM3354 is also available with standard output voltages of 1.8V, 3.3V, 3.7V, 4.1V (ideal for white LED applications), and 5.0V. If other output voltage options between 1.8V and 5.0V are desired, please contact your National Semiconductor representative. The LM3354’s proprietary buck-boost architecture enables up to 90mA 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 LM3354 is available in a 10-pin MSOP package. This package has a maximum height of only 1.1 mm. The high efficiency of the LM3354, 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 or the LM3355 for up to 50mA of output current. Features n Regulated VOUT with ± 3% accuracy n Standard output voltages of 1.8V, 3.3V, 4.1V, and 5.0V also available n Custom output voltages available from 1.8V to 5.0V in 100 mV increments with volume order n 2.5V to 5.5V input voltage range n Up to 90mA 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 typical switching frequency 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 Li-Ion, NiCd, NiMH, or alkaline battery powered systems Typical Operating Circuit 20057301 © 2002 National Semiconductor Corporation DS200573 www.national.com LM3354-3.7 Connection Diagram 20057302 Top View MSOP-10 Pin Package See NS Package Number MM Ordering Information Order Number LM3354MMX-3.7 LM3354MM-3.7 Package Type MSOP-10 MSOP-10 NSC Package Drawing MUB10A MUB10A Supplied As 3.5k Units, Tape and Reel 1k Units, Tape and Reel Pin Description Pin Number 1 2 3 4 5 6 7 8 9 10 Name VIN C1− C1+ GND GND CFIL SD VOUT C2− C2+ Input Supply Voltage Negative Terminal for C1 Positive Terminal for C1 Ground Ground Filter Capacitor, a 1µF capacitor is recommended. Shutdown, active low Regulated Output Voltage Negative Terminal for C2 Positive Terminal for C2 Function www.national.com 2 LM3354-3.7 Absolute Maximum Ratings (Note 1) 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.) −0.5V to 5.6V Internally Limited 150˚C 250˚C/W −65˚C to +150˚C 260˚C ESD Rating (Note 3) Human Body Model Machine Model 1.5 kV 100V Operating Ratings Input Voltage (VIN) Output Voltage (VOUT) Ambient Temperature (TA) (Note 2) Junction Temperature (T J) (Note 2) 2.5V to 5.5V 1.8V to 5.0V −40˚C to +85˚C −40˚C to +120˚C Electrical Characteristics Limits in standard typeface are for TA = 25˚C, and limits in boldface type apply over the full operating temperature range. Unless otherwise specified: C1 = C2 = 0.33 µF; CIN = 10 µF; COUT = 10 µF; CFIL = 1 µF; VIN = 3.5V. Parameter LM3354-3.7 Output Voltage (V OUT) VIN = (2.7, 5.5) V IL = (1, 70) mA VIN = (2.8, 4.0) V IL = (1, 90) mA VIN = (4.3, 5.5) V IL = (1, 90) mA Efficiency Output Voltage Ripple (Peak-to-Peak) ILOAD = 15 mA ILOAD= 70 mA ILOAD = 50 mA C OUT = 10 µF ceramic 3.589/3.552 3.589/3.552 3.589/3.552 3.7 3.7 3.7 75 70 75 3.811/3.848 3.811/3.848 3.811/3.848 % V Conditions Min (Note 5) Typ (Note 4) Max (Note 5) Units mVP-P LM3354-ALL OUTPUT VOLTAGE VERSIONS Operating Quiescent Measured at Pin Current VIN; I LOAD = 0A (Note 6) Shutdown Quiescent SD Pin at 0V (Note Current 7) Switching Frequency SD Input Threshold Low SD Input Threshold High SD Input Current 2.5V < VIN < 5.5V 2.5V < VIN < 5.5V Measured at SD Pin; SD Pin = VIN = 5.5V 0.8 VIN 0.6 375 2.3 1 475 5 1.4 0.2 VIN µA µA MHz V 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 +120˚C except for the 5V output option. The 5V option requires that TA ≤ +60˚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). 3 www.national.com LM3354-3.7 Electrical Characteristics (Continued) 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. www.national.com 4 LM3354-3.7 Typical Performance Characteristics VOUT vs. VIN Unless otherwise specified TA = 25˚C. VOUT vs. VIN 20057341 20057342 Efficiency vs. VIN Load Transient Response 20057314 20057320 Operating Quiescent Current vs. VIN Switching Frequency vs. VIN 20057324 20057323 5 www.national.com LM3354-3.7 Typical Performance Characteristics Unless otherwise specified TA = 25˚C. Maximum VOUT Ripple vs. COUT (Continued) Maximum VOUT Ripple vs. COUT 20057332 20057330 www.national.com 6 LM3354-3.7 Applications Information 20057303 FIGURE 1. Block Diagram Operating Principle The LM3354 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 LM3354 can provide a regulated voltage between 1.8V and 5.0V from an input voltage between 2.5V and 5.5V. It can supply a load current up to 90 mA (refer to Electrical Characteristics). As shown in Figure 1, the LM3354 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 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. 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. Filter Capacitor Selection a) CAPACITOR TECHNOLOGIES The three major technologies of capacitors that can be used as filter capacitors for LM3354 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). 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 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. 7 www.national.com LM3354-3.7 Filter Capacitor Selection iii) Polymer Electrolytic (Continued) 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. TABLE 1. Comparison of Capacitor Technologies Ceramic ESR Relative Height Relative Footprint Temperature Stability Frequency Stability VOUT Ripple Magnitude @ < 50 mA VOUT Ripple Magnitude @ > 100 mA dv/dt of VOUT Ripple @ All Loads b) CAPACITOR SELECTION 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. ii) Input Capacitor (CIN) 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 Lowest Low for Small Values ( < 10 µF); Taller for Higher Values Large X7R/X5R-Acceptable Good Low Low Lowest High Lowest Small Good Acceptable High Slightly Higher High Tantalum Polymer Electrolytic Low Low Largest Good Good Low Low Low 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 90 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. 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 LM3354. Of the different capacitor technologies, a sample of vendors that have been verified as suitable for use with the LM3354 are shown in Table 2. TABLE 2. Capacitor Vendor Information Manufacturer Ceramic Taiyo-yuden AVX Sprague/Vishay Tantalum Nichicon Polymer Electrolytic Cornell-Dubilier (ESRD) Sanyo (POSCAP) (847) 843-7500 (508) 996-8561 (619) 661-6322 (847) 843-2798 (508) 996-3830 (619) 661-1055 www.nichicon.com www.cornell-dubilier.com www.sanyovideo.com Tel (408) 573-4150 (803) 448-9411 (207) 324-4140 Fax (408) 573-4159 (803) 448-1943 (207) 324-7223 Website www.t-yuden.com www.avxcorp.com www.vishay.com www.national.com 8 LM3354-3.7 Maximum Load Under Start-Up Due to the LM3354’s unique start-up sequence, it is not able to start up under all load conditions. Starting with 60 mA or less will allow the part to start correctly under any temperature or input voltage conditions. After the output is in regulation, any load up to the maximum as specified in the Electrical Characteristics may be applied. Using a Power On Reset circuit, such as the LP3470, is recommended if greater start up loads are expected. Under certain conditions the LM3354 can start up with greater load currents without the use of a Power On Reset Circuit. Thermal Protection During output short circuit conditions, the LM3354 will draw high currents causing a rise in the junction temperature. On-chip thermal protection circuitry disables the charge 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. Typical Application Circuits 20057333 FIGURE 2. Basic Buck/Boost Regulator 20057315 FIGURE 3. Low Output Noise and Ripple Buck/Boost Regulator 9 www.national.com LM3354-3.7 Typical Application Circuits (Continued) 20057340 FIGURE 4. White LED Driver Driving Light Emitting Diodes The LM3354 can be used to drive LED’s of nearly any color. The 4.1V option is ideal for driving the White LED’s required for the backlight of small color displays. Figure 4 shows the circuit used to power White LED’s. The LED current is set by the resistors RB by using the equation ILED = (4.1V − VF)/RB where VF is the typical forward voltage drop of the LED used. The brightness of the diodes may be controlled using the shutdown pin. A PWM signal on the shutdown pin may be used to adjust the brightness by varying the duty cycle. A signal between 60Hz and 200Hz may be used for best linearity. In this case the equivalent LED current is approxi- mately equal to the maximum current multiplied by the duty cycle. Using frequencies above 200Hz may cause less linear results as the charge and discharge time of the output capacitor becomes more significant. Layout Considerations Due to the 1 MHz typical switching frequency of the LM3354, careful board layout is a must. It is important to place the 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. Figure 5 shows a typical layout as used in the LM3354 evaluation board. 20057316 FIGURE 5. Typical Layout, Top View (magnification 1.5X) www.national.com 10 LM3354-3.7 Regulated 90mA Buck-Boost Switched Capacitor DC/DC Converter Physical Dimensions unless otherwise noted inches (millimeters) 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. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 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