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NATIONAL SEMICONDUCTOR LM2771 Manual

1. Leadless Leadframe Package LLP Note 5 The Human body model is a 100pF capacitor discharged through a 1 5kQ resistor into each pin The machine model is a 200pF capacitor discharged directly into each pin MIL STD 883 3015 7 Note 6 Maximum ambient temperature Ta Mmax is dependent on the maximum operating junction temperature Ty jax op 110 C the maximum power dissipation of the device in the application Pp jax and the junction to ambient thermal resistance of the part package in the application Oja as given by the following equation TA MAX TJ MAX OP E OJA X Pp MAX Note 7 Junction to ambient thermal resistance is highly application and board layout dependent In applications where high maximum power dissipation exists special care must be paid to thermal dissipation issues Note 8 Min and Max limits are guaranteed by design test or statistical analysis Typical numbers are not guaranteed but do represent the most likely norm Note 9 Cin Cour C1 Low ESR Surface Mount Ceramic Capacitors MLCCs used in setting electrical characteristics Note 10 Voyrt is set to 1 6V during this test Note 11 Open loop output resistance can be used to predict output voltage when under low Viy and high lour conditions Voyt falls out of regulation Vout Vin 2 Rot X lout Note 12 Maximum input current is equal to half the maximum output current for buck mode switched capacitor converters Note 13 There is a 350kQ pull down res
2. 2 7V to 5 5V Input Range Shutdown Disconnects Load from Vin 1 1MHz Switching Frequency No Inductors Small Solution Size Current Limit and Thermal Protection LLP 10 Package 8mm x 3mm x 0 8mm Applications m DSP Memory and Microprocessor Power Supplies Mobile Phones and Pagers Portable Electronic Devices LM2771 Efficiency vs March 2006 Low Dropout Linear Regulator LDO Efficiency 100 90 EFFICIENCY 3 5 INPUT VOLTAGE V 4 0 4 5 20183813 www national com J9BAUOD OG OG UMOG dajs 10 9ede p y mS YwosZ ddiy mo7 LZZZNT LM2771 Connection Diagram and Package Mark Information 10 Pin Non Pullback Leadless Frame Package LLP 10 National Semiconductor Package Number SDA10A Die Attach 3 Die Attach Pad GND Pad GND Top View Bottom View Package Marking Top View Note The actual physical placement of the package marking will vary from part to part The package marking placeholder XXXXX is a code for die traceability YYYYY identifies the device part number voltage option etc See the Order Information table below for the device ID codes DN 20183802 Pin Descriptions Pin Name Description 1 Input Voltage Recommended Vn operating range 3 0V to 5 5V 2 GND Ground 3 Output Voltage 4 No Connect 5 No Connect 6 Flying Capacitor 1 Negative Terminal 7 Flying Capacitor 1 Positive Terminal 8 No Connect 9 GND Ground 10 EN Enable Pin Logic Input Applying a logic H
3. 4 7uF T 25 C Capacitors are low ESR multi layer ceramic capacitors MLCC s Continued Load Step 15mA to 200mA 20183823 20183824 CH2 Voyt Scale 20mV Div AC Coupled CH2 Vout Scale 20mV Div AC Coupled CH4 lour Scale 200mA Div CH4 lour Scale 200mA Div Time scale 20us Div Time scale 10us Div Line Step 3 6V to 4 5V with Load 7 5Q 200mA Oscillator Frequency vs Input Voltage 1200 N IL 1150 gt O Z wW 1100 O ar u 1050 oc x 1000 fa P 950 20183822 900 CH1 Vin Scale 1V Div AC Coupled 3 0 3 5 4 0 4 5 5 0 5 5 CH2 Vout Scale 20mV Div AC Coupled INPUT VOLTAGE V Time scale 40us Div 20183825 Startup and Shutdown Behavior Load 60 250mA 20183816 CH1 Ven Scale 2V Div DC Coupled CH2 Voyt Scale 500mV Div DC Coupled Time scale 100us Div www national com 6 Operation Description OVERVIEW The LM2771 is a switched capacitor converter that produces a regulated low voltage output The core of the part is a highly efficient charge pump that utilizes fixed frequency pre regulation and Pulse Frequency Modulation to minimize ripple and power losses over wide input voltage and output current ranges A description of the principal operational characteristics of the LM2771 is detailed in the Circuit De scription and Efficiency Performance sections These sections refer to details in the Block Diagram CIRCUIT DESCRIPTION The core of the LM2771 is a two phase
4. rating will usually minimize DC bias effects Consult capaci tor manufacturers for information on capacitor DC bias char acteristics Capacitance characteristics can vary quite dramatically with different application conditions capacitor types and capaci tor manufacturers It is strongly recommended that the LM2771 circuit be thoroughly evaluated early in the design in process with the mass production capacitors of choice This will help ensure that any such variability in Capacitance does not negatively impact circuit performance The table below lists some leading ceramic capacitor manu facturers Contact Information Murata www murata com www component tdk com OUTPUT CAPACITOR AND OUTPUT VOLTAGE RIPPLE The output capacitor in the LM2771 circuit Cour directly impacts the magnitude of output voltage ripple Other promi nent factors also affecting output voltage ripple include input voltage output current and flying capacitance Due to the complexity of the regulation topology providing equations or models to approximate the magnitude of the ripple can not be easily accomplished But one important generalization can be made increasing decreasing the output capaci tance will result in a proportional decrease increase in output voltage ripple In typical high current applications a 4 7uF low ESR ce ramic output capacitor is recommended Different output Capacitance values can be used to reduce ripple shrink the s
5. 8790
6. A typ the LM2771 automatically switches to a low ripple Pulse Frequency Modulation PFM form of regulation In PFM mode the flying capacitor stays in the discharge phase until the output voltage drops below a predetermined trip point When this occurs the flying capacitor switches back to the charge phase After being charged the flying capacitor repeats the process of staying in the discharge phase and switching to the charge phase when necessary EFFICIENCY PERFORMANCE Charge pump efficiency is derived in the following two ideal equations supply current and other losses are neglected for simplicity lin G x lour E Vout X lout Vin X lin Vout G x Vin In the equations G represents the charge pump gain Effi ciency is at its highest as GxV approaches Vour Refer to the efficiency graph in the Typical Performance Character istics section for detailed efficiency data The transition between Pass mode and the gain of 12 is clearly distin guished by the sharp discontinuity in the efficiency curve SHUTDOWN The LM2771 is in shutdown mode when the voltage on the enable pin EN is logic low In shutdown the LM2771 draws virtually no supply current When in shutdown the output of the LM2771 is completely disconnected from the input The internal feedback resistors will pull the output voltage down to OV SOFT START The LM2771 employs soft start circuitry to prevent excessive input inrush currents during start
7. IGH voltage signal enables the part ee A logic LOW voltage signal places the the device in shutdown Order Information Output Voltages Order Number Package Mark ID Supplied as 1 5V LM2771SD XXXXX CZC2CX 1000 Units Tape and Reel YYYYY L2771 SDA10A 1 5V LM2771SDX XXXXX CZC2CX Non Pullback LLP 4500 Units Tape and Reel YYYYY L277 1 www national com 2 Absolute Maximum Ratings notes 1 2 If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office Operating Ratings notes 1 2 Input Voltage Range 2 7V to 5 5V OmA to 250mA 30 C to 110 C Distributors for availability and specifications Recommended Load Current Range Junction Temperature T Range Vin Pin Voltage 0 3V to 6 0V l l Ambient Temperature T Range 30 C to 85 C EN Pin Voltage 0 3V to Vin 0 3V Note 6 w 6 0V max Continuous Power Dissipation Note 3 Internally Limited Thermal Properties Junction Temperature Tj max 150 C Junction to Ambient Thermal 55 C W Storage Temperature Range 65 C to 150 C Resistance 6 LLP10 Package Maximum Lead Temperature 265 C Note 7 Note 4 ESD Rating Note 5 Human Body Model 2 0kV Machine Model 200V Electrical Characteristics Notes 2 8 Limits in standard typeface are for T 25 C Limits in boldface type apply over the full operating junction temperature range 30 C lt T lt 110 C Unless otherwise noted s
8. National Semiconductor LM2771 Low Ripple 250mA Switched Capacitor Step Down DC DC Converter General Description The LM2771 is a switched capacitor step down regulator that produces a 1 5V output without the use of an inductor It is capable of supplying loads up to 250mA The LM2771 operates with an input voltage from 2 7V to 5 5V and re quires only 3 low cost ceramic capacitors The LM2771 uses a regulated 0 5x charge pump to give power conversion efficiencies nearly twice as high as an LDO Pre regulated 1 1MHz fixed frequency switching re sults in very low ripple and noise on both the input and the output When output currents are low lt 30mA typ the part automatically switches to a low ripple PFM regulation mode to maintain high efficiency over the entire load range At input voltages below 3 5V Typ the charge pump goes into pass mode with efficiencies similar to an LDO The LM2771 is available in National s 10 pad Leadless Leadframe No Pullback Package LLP 10 Typical Application Circuit Vout 1 5V louT up to 250 mA VIN 3 0V to 5 5V LM2771 Capacitors 1 uF TDK C1005X5R1A105K 4 7 uF TDK C1608X5RO0J475K or equivalent 20183801 2006 National Semiconductor Corporation DS201838 Features Low Noise Fixed Frequency Operation 1 5V Output Voltage Li lon 3 6V to 1 5V with 81 Efficiency 1 7 Output Voltage Accuracy Very Low Output Ripple 8mV 250mA Output Currents up to 250mA
9. arized capacitors tantalum aluminum electrolytic etc must not be used for the flying capacitor as they could become reverse biased during LM2771 operation RECOMMENDED CAPACITOR CONFIGURATIONS The data in Table 1 can be used to assist in the selection of a capacitor configuration that best balances solution size and cost with the electrical requirements of the application As previously discussed input and output ripple voltages will vary with output current and input voltage The numbers provided show expected ripple voltage when Vin 3 6V and load currents are between 10mA and 200mA The table offers first look at approximate ripple levels and provides a comparison for the different capacitor configurations pre sented but is not intended to be a guarantee of perfor mance Application Information Continuea Layout Guidelines Proper board layout will help to ensure optimal performance TABLE 1 LM2771 Performance with Different of the LM2771 circuit The following guidelines are recom Capacitor Configurations Note 14 mended CAPACITOR TYPICAL TYPICAL e Place capacitors as close to the LM2771 as possible and CONFIGURATION INPUT OUTPUT preferably on the same side of the board as the IC Vin 3 6V RIPPLE RIPPLE e Use short wide traces to connect the external capacitors to the LM2771 to minimize trace resistance and induc tance e Use alow resistance connection between ground and the GND pin of the LM2771 Using wid
10. charge pump con trolled by an internally generated non overlapping clock The charge pump operates by using an external flying capacitor C1 to transfer charge from the input to the output At input voltages below 3 5V typ the LM2771 operates in a pass mode with the input current being equal to the load current At input voltages above 3 5V typ the part utilizes a gain of 12 resulting in an input current equal to half the load current The two phases of the switched capacitor switching cycle will be referred to as the charge phase and the discharge phase During the charge phase the flying capacitor is charged by the input supply After half of the switching cycle t 1 2xFsy the LM2771 switches to the discharge phase In this configuration the charge that was stored on the flying capacitor in the charge phase is transferred to the output The LM2771 uses fixed frequency pre regulation to regulate the output voltage to 1 5V during moderate to high load currents The input and output connections of the flying capacitor is made with internal MOS switches Pre regulation limits the gate drive of the MOS switch connected between the voltage input and the flying capacitor Control ling the on resistance of this switch limits the amount of charge transferred into and out of the flying capacitor during the charge and discharge phases and in turn helps to keep the output ripple very low When output currents are low lt 30m
11. e traces and or mul tiple vias to connect GND to a ground plane on the board is most advantageous Cin 0 47uF Cour 4 7pF C 1uF Cin 0 47pF Cour 3 3pF C 1yF Cin 0 47uF Cour 3 3pF C 0 33uF Note 14 Refer to the text in the Recommended Capacitor Configurations section for detailed information on the data in this table 9 www national com LZZcIN1 LM2771 Low Ripple 250mA Switched Capacitor Step Down DC DC Converter Physical DiMeNSIONS inches millimeters unless otherwise noted ae DIMENSIONS ARE IN MILLIMETERS DIMENSIONS IN FOR REFERENCE ONLY Fao aozas h l a RECOMMENDED LAND PATTERN 10X 0 6 PIN 1 INDEX AREA 3 0 1 E O E GID 10 fle 10X 0 40 1 10x aan 0 1 c A sO 8x 0 5 K 2x SDA10A Rev A SDA10A 10 Pin Non Pullback Leadless Leadframe Package 3 0mm x 3 0mm x 0 8mm 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 For the most current product information visit us at www national com 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 suppor
12. istor connected internally between the EN pin and GND Block Diagram LM2771 VIN SWITCH aig ARRAY GND C1 V PFM Current OUT Control Sense 1 1 MHz OSC EN EN Enable Shutdown Control Soft Start Ramp 20183803 www national com 4 Typical Performance Characteristics unless otherwise specified Vin 3 6V Cn C 1 0pF Cour 4 7UF Ta 25 C Capacitors are low ESR multi layer ceramic capacitors MLCC s Output Voltage vs Input Voltage 1 53 lour OMA ee a 1 52 EO ee d eee Ty 30 C T 25 C Ty 85 C 1 51 OUTPUT VOLTAGE V on O INPUT VOLTAGE V 20183812 Efficiency vs Input Voltage EFFICIENCY 0 3 0 3 5 4 0 4 5 5 0 5 5 INPUT VOLTAGE V 20183813 Input Voltage Ripple Load 602 250mA 20183815 CH1 Vin Cin 1pF Scale 50mV Div AC Coupled CH2 Vin Cin 10UF Scale 50mV Div AC Coupled Time scale 200ns Div OUTPUT VOLTAGE V EFFICIENCY Output Voltage vs Output Current 1 53 1 52 OUTPUT CURRENT mA 20183814 Efficiency vs Output Current i H i iin lll Ca Di Sini rl 0 0 1 1 100 1000 OUTPUT CURRENT mA 20183826 ae athe Ripple Load aaa E a OE IOE O OR OR i t 20183821 CH2 Vout Court 4 7HF Scale 20mV Div AC Coupled Time scale 200ns Div www national com LZZcIN1 LM2771 Typical Performance Characteristics uniess otherwise specified Vin 3 6V Cin C4 1 0UF Cour
13. olution size and or cut the cost of the solution But chang ing the output capacitor may also require changing the flying capacitor and or input capacitor to maintain good overall circuit performance Performance of the LM2771 with differ ent capacitor setups in discussed in the section Recom mended Capacitor Configurations High ESR in the output capacitor increases output voltage ripple If a ceramic capacitor is used at the output this is usually not a concern because the ESR of a ceramic capaci tor is typically very low and has only a minimal impact on ripple magnitudes If a different capacitor type with higher ESR is used tantalum for example the ESR could result in high ripple To eliminate this effect the net output ESR can be significantly reduced by placing a low ESR ceramic ca www national com pacitor in parallel with the primary output capacitor The low ESR of the ceramic capacitor will be in parallel with the higher ESR resulting in a low net ESR based on the prin ciples of parallel resistance reduction INPUT CAPACITOR AND INPUT VOLTAGE RIPPLE The input capacitor Cn is a reservoir of charge that aids a quick transfer of charge from the supply to the flying capaci tor during the charge phase of operation The input capacitor helps to keep the input voltage from drooping at the start of the charge phase when the flying capacitor is connected to the input It also filters noise on the input pin keeping this noi
14. pecifications apply to the LM2771 Typical Application Circuit pg 1 with Vin Vout 1 5V Output Voltage Regulation 3 0V lt Vin lt 5 5V 1 455 1 5 1 545 V oms onszoma dero era 3 0V lt Vn lt 5 5V 1 475 1 5 1 525 3 0V lt Vn lt 5 5V 1 445 1 5 1 545 rol osa D aa OMA lt lour lt 250MA Vout loyur Output Load Regulation Vout 1 5V Co f Cd o Vout Vin Output Line Regulation lo Quiescent Supply Current lour OMA 45 UA Note 10 Note 11 lo Output Current Limit Vin 5 5V 500 mA OV lt Vour lt 0 2V i S on o m Logic high Input Current V EN 1 8V Pf ey HA Note 13 Note 1 Absolute Maximum Ratings indicate limits beyond which damage to the component may occur Operating Ratings are conditions under which operation of the device is guaranteed Operating Ratings do not imply guaranteed performance limits For guaranteed performance limits and associated test conditions see the Electrical Characteristics tables Note 2 All voltages are with respect to the potential at the GND pins Note 3 Internal thermal shutdown circuitry protects the device from permanent damage Thermal shutdown engages at Tj 150 C typ and disengages at Ty 140 C typ 3 www national com LZZcIN1 LM2771 Electrical Characteristics Notes 2 8 Continued Note 4 For detailed information on soldering requirements and recommendations please refer to National Semiconductor s Application Note 1187 AN 1187
15. ries resistance ESR lt 15mQ typ Tantalum capacitors OS CON capacitors and alumi num electrolytic capacitors generally are not recommended for use with the LM2771 due to their high ESR as compared to ceramic capacitors For most applications ceramic capacitors with an X7R or X5R temperature characteristic are preferred for use with the LM2771 These capacitors have tight capacitance tolerance as good as 10 and hold their value over temperature X7R 15 over 55 C to 125 C X5R 15 over 55 C to 85 C Capacitors with a Y5V or Z5U temperature characteristic are generally not recommended for use with the LM2771 These types of capacitors typically have wide capacitance toler ance 80 20 and vary significantly over temperature Y5V 22 82 over 30 C to 85 C range Z5U 22 56 over 10 C to 85 C range Under some conditions a 1puF rated Y5V or Z5U capacitor could have a capacitance as low as 0 1uF Such detrimental deviation is likely to cause Y5V and Z5U capacitors to fail to meet the minimum capaci tance requirements of the LM2771 www national com LZZcIN1 LM2771 Application Information continued Net capacitance of a ceramic capacitor decreases with in creased DC bias This degradation can result in lower ca pacitance than expected on the input and or output resulting in higher ripple voltages and currents Using capacitors at DC bias voltages significantly below the capacitor voltage
16. se out of sensitive internal analog circuitry that is biased off the input line Much like the relationship between the output capacitance and output voltage ripple input capacitance has a dominant and first order effect on input ripple magnitude Increasing decreasing the input capacitance will result in a propor tional decrease increase in input voltage ripple Input volt age output current and flying capacitance also will affect input ripple levels to some degree In typical high current applications a 1uF low ESR ceramic Capacitor is recommended on the input Different input ca pacitance values can be used to reduce ripple shrink the solution size and or cut the cost of the solution But chang ing the input capacitor may also require changing the flying capacitor and or output capacitor to maintain good overall circuit performance Performance of the LM2771 with differ ent capacitor setups is discussed below in Recommended Capacitor Configurations FLYING CAPACITOR The flying capacitor C transfers charge from the input to the output Flying capacitance can impact both output cur rent capability and ripple magnitudes If flying capacitance is too small the LM2771 may not be able to regulate the output voltage when load currents are high On the other hand if the flying capacitance is too large the flying capacitor might overwhelm the input and output capacitors resulting in in creased input and output ripple Pol
17. t devices or systems are devices or systems 2 A critical component is any component of a life support which a are intended for surgical implant into the body or device or system whose failure to perform can be reasonably b support or sustain life and whose failure to perform when expected to cause the failure of the life support device or properly used in accordance with instructions for use system or to affect its safety or effectiveness provided in the labeling can be reasonably expected to result in a significant injury to the user BANNED SUBSTANCE COMPLIANCE National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products Stewardship Specification CSP 9 111C2 and the Banned Substances and Materials of Interest Specification CSP 9 111S2 and contain no Banned Substances as defined in CSP 9 111S2 Leadfree products are ROHS compliant National Semiconductor National Semiconductor National Semiconductor National Semiconductor Americas Customer Europe Customer Support Center Asia Pacific Customer Japan Customer Support Center Support Center Fax 49 0 180 530 85 86 Support Center Fax 81 3 5639 7507 Email new feedback nsc com Email europe support nsc com Email ap support nsc com Email jon feedback nsc com Tel 1 800 272 9959 Deutsch Tel 49 0 69 9508 6208 Tel 81 3 5639 7560 English Tel 44 0 870 24 0 2171 www national com Fran ais Tel 33 0 1 41 91
18. up At startup the output voltage gradually rises from OV to the nominal output volt age This occurs in 150us typ Soft start is engaged when the part is enabled including situations where voltage is established simultaneously on the V and EN pins THERMAL SHUTDOWN Protection from damage related to overheating is achieved with a thermal shutdown feature When the junction tem perature rises to 150 C typ the part switches into shut down mode The LM2771 disengages thermal shutdown when the junction temperature of the part is reduced to 140 C typ Due to the high efficiency of the LM2771 thermal shutdown and or thermal cycling should not be en countered when the part is operated within specified input voltage output current and ambient temperature operating ratings If thermal cycling is seen under these conditions the most likely cause is an inadequate PCB layout that does not allow heat to be sufficiently dissipated out of the LLP pack age CURRENT LIMIT PROTECTION The LM2771 charge pump contains current limit protection circuitry that protects the device during Vour fault conditions where excessive current is drawn Output current is limited to 500mA typ Application Information RECOMMENDED CAPACITOR TYPES The LM2771 requires 3 external capacitors for proper opera tion Surface mount multi layer ceramic capacitors are rec ommended These capacitors are small inexpensive and have very low equivalent se

NATIONAL SEMICONDUCTOR LM2771 Manual

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