LM2611 1.4MHz Converter LM2611 current mode, inverting switching

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LM2611 1.4MHz Converter LM2611 current mode, inverting switching

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LM2611 1.4MHz Converter
LM2611 1.4MHz Converter
LM2611 current mode, inverting switching regulator. Operating from supply, capable producing regulated negative output voltage -(36VIN(MAX)). LM2611 utilizes input output inductor, which enables voltage ripple current both input output. With switching frequency 1.4MHz, inductors output capacitor physically small cost. High efficiency achieved through RDS(ON) FET. LM2611 features shutdown pin, which activated when part needed lower save battery life. negative feedback (NFB) provides simple method setting output voltage, using just resistors. Cycle-by-cycle current limiting internal compensation further simplify LM2611. LM2611 available small SOT23-5 package. comes grades: Grade Current Limit RDS(ON) 1.2A Grade 0.9A
Features
1.4MHz switching frequency RDS(ON) DMOS 1mVp-p output ripple 300mA from input Better regulation than charge pump Uses tiny capacitors inductors Wide input range: 2.7V shutdown current: 5-lead SOT-23 package
Applications
Head Bias Digital camera bias bias GaAs bias Positive negative conversion
Typical Application Circuit
20018117
2005 National Semiconductor Corporation
DS200181
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LM2611
Connection Diagram
View
20018115
5-lead SOT-23 Package Package Number MF05A
Ordering Information
Order Number LM2611AMF LM2611AMFX LM2611BMF LM2611BMFX SOT23-5 MF05A Package Type Package Drawing Supplied Tape Reel Tape Reel Tape Reel Tape Reel Package S40A S40A S40B S40B
Description
Name SHDN Analog power ground. Negative feedback. Connect output external resistor divider output voltage. Shutdown control input. Device Ground Device shutdown. Analog power input. Filter high frequency noise with ceramic capacitor placed close pin. Function Drain internal switch. Connect node input inductor capacitor.
Block Diagram
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LM2611
Absolute Maximum Ratings (Note
Military/Aerospace specified devices required, please contact National Semiconductor Sales Office/ Distributors availability specifications. Voltage Voltage SHDN Voltage Maximum Junction Temperature Power Dissipation (Note Lead Temperature 14.5V 14.5V 125°C Internally Limited 300°C
Susceptibility (Note Human Body Model Machine Model 200V
Operating Conditions
Operating Junction Temperature Range Storage Temperature Supply Voltage -40°C +125°C -65°C +150°C 2.7V 256°C/W
Electrical Characteristics
Specifications standard type face 25°C those with boldface type apply over Temperature Range -40°C +85°C, unless otherwise specified. 5.0V unless otherwise specified. Symbol RDSON SHDNTH ISHDN INFB Parameter Input Voltage Switch Current Limit Switch Resistance Shutdown Threshold Shutdown Bias Current Negative Feedback Reference Bias Current Quiescent Current Grade Grade Grade Grade Device enabled Device disabled VSHDN VSHDN VNFB =-1.23V VSHDN Switching VSHDN Switching VSHDN %VOUT/ DMAX Reference Line Regulation Switching Frequency Maximum Duty Cycle Switch Leakage Switching 2.7V -1.205 -2.7 -1.23 -4.7 0.024 0.02 -1.255 -6.7 0.50 Conditions (Note 0.65 (Note (Note Units
Note Absolute maximum ratings limits beyond which damage device occur. Operating Ratings conditions which device intended functional, device parameter specifications guaranteed. guaranteed specifications test conditions, Electrical Characteristics. Note maximum allowable power dissipation function maximum junction temperature, TJ(MAX), junction-to-ambient thermal resistance, ambient temperature, Electrical Characteristics table thermal resistance various layouts. maximum allowable power dissipation ambient temperature calculated using: (MAX) (TJ(MAX) TA)/JA. Exceeding maximum allowable power dissipation will cause excessive temperature, regulator will into thermal shutdown. Note human body model capacitor discharged through 1.5k resistor into each pin. machine model 200pF capacitor discharged directly into each pin. Note limits guaranteed room temperature (standard typeface) temperature extremes (bold typeface). room temperature limits 100% tested guaranteed through statistical analysis. limits temperature extremes guaranteed correlation using standard Statistical Quality Control (SQC) methods. limits used calculate Average Outgoing Quality Level (AOQL). Note Typical numbers 25°C represent expected value parameter.
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LM2611
Typical Performance Characteristics
RDS(ON) RDS(ON) Ambient Temperature
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Switch Current Limit
Switch Current Limit Ambient Temperature
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Oscillator Frequency
Oscillator Frequency Ambient Temperature
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LM2611
Typical Performance Characteristics
VNFB 25°C, VOUT
(Continued) VNFB Ambient Temperature
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INFB 25°C, VOUT
INFB Ambient Temperature 3.5V, VOUT
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Ambient Temperature Load)
VSHUTDOWN Ambient Temperature
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LM2611
Operation
Converter
20018105
FIGURE Operating Cycles Converter LM2611 current mode, fixed frequency switching regulator with -1.23V reference that makes ideal converter. converter inverts input step step down absolute value. Using inductors both input output, converter produces very little input output current ripple. This significant advantage over other inverting topologies such buck-boost flyback. operating states converter shown Figure During first cycle, transistor switch closed diode open. charged source charged CCUK, while output current provided second cycle, charges CCUK discharges through load. applying volt-second balance either inductors, relationship VOUT duty cycle found
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FIGURE Voltage Current Waveforms Inductor Converter following sections review steady-state design LM2611 converter. Output Input Inductor Figure Figure show steady-state voltage current waveforms respectively. Referring Figure (a), when switch closed, applied across next cycle, switch opens diode becomes forward biased, VOUT applied across (the voltage across CCUK VOUT. voltage current waveforms inductor shown Figure During first cycle operation, when switch closed, applied across When switch opens, VOUT applied across
20018104
FIGURE Voltage Current Waveforms Inductor Converter
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LM2611
Operation
(Continued)
Input Capacitor input current waveform converter continuous triangular, shown Figure input inductor insures that input capacitor sees fairly ripple currents. However, input inductor gets smaller, input ripple goes current input capacitor given
following equations define values given Figure Figure IOUT
these equations choose correct core sizes inductors. design LM2611's internal compensation assumes equal thus recommended stay within this range. Switch Current Limit LM2611 incorporates separate current limit comparator, making current limit independent other variables. current limit comparator measures switch current versus reference that represents current limit. time switch current surpasses current limit, switch opens until next switching period. determine maximum load given conditions, both input output inductor currents must considered. switch current equal iL2, drawn Figure summary:
input capacitor should capable handling current. Although input capacitor critical converter, 10µF higher value good quality capacitor prevents impedance interactions with input supply. 0.1µF ceramic bypass capacitor also recommended (pin This capacitor must connected very close (within inches). Output Capacitor Like input current, output current also continuous, triangular, ripple (see Figure output capacitor must rated handle current:
ISW(PEAK) must less than current limit (1.2A typical), will also limited thermal resistivity LM2611's SOT23-5 package 265°C/W).
example, ICOUT(RMS) range from 30mA 180mA with 10µH L1,2 22µH, -10V VOUT -3.3V, 2.7V (VIN using separate power analog supplies, Split Supply Operation APPLICATIONS section). worst case conditions with L1,2, VOUT(MAX), VIN(MAX). Many capacitor technologies will provide this level current, ceramic capacitors ideally suited LM2611. Ceramic capacitors provide good combination capacitance equivalent series resistance (ESR) keep zero formed capacitance high frequencies. zero calculated
general rule thumb keep fESR 80kHz LM2611 designs. tantalum capacitors will usually rated least 180mA voltage rating above. However tantalum capacitor (even tantalum capacitor) much higher than ceramic capacitor could place fESR enough cause LM2611 unstable.
20018102
FIGURE Switch Current Waveform Converter. peak value equal average currents through average-to-peak current ripples through
Improving Transient Response/Compensation compensator LM2611 internal. However, zero-pole pair added open loop frequency response inserting feed forward capacitor, CFF, parallel feedback resistor (RFB1). Phase margin bandwidth improved with added zero-pole pair. This inturn will improve transient response step load change (see Figure Figure position zero-pole pair function feedback resistors capacitor value:
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LM2611
Operation
(Continued)
optimal position this zero-pole pair will vary with circuit parameters such IOUT, COUT, CCUK. most cases, value zero frequency between kHz. Notice pole position, dependant feedback resistors RFB1 RFB2, therefore also dependant output voltage. output voltage becomes closer -1.26V, pole moves towards zero, tending cancel out. absolute magnitude output voltage less than 3.3V, adding zero-pole pair will have much effect response.
20018122
LEVEL
FIGURE 130mA 400mA Transient Response circuit Figure with disconnected Hysteretic Mode output current decreases, there will come point when energy stored capacitor more than energy required load. excess energy absorbed output capacitor, causing output voltage increase regulation. LM2611 detects when this happens enters pulse skipping, hysteretic mode. hysteretic mode, output voltage ripple will increase, illustrated Figure Figure
20018120
LEVEL
FIGURE 130mA 400mA Transient Response circuit Figure with
20018121
FIGURE LM2611 mode very ripple
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LM2611
Operation
(Continued)
20018123
FIGURE loads, LM2611 enters pulse-skipping mode. output ripple slightly increases this mode. Thermal Shutdown junction temperature LM2611 exceeds 163°C, will enter thermal shutdown. thermal shutdown, part deactivates driver switch turns off. switch remains until junction temperature drops 155°C, which point part begins switching again. will typically take 10ms junction temperature drop from 163°C 155°C with switch off.
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LM2611
Application Circuits
Inverting Converter
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Efficiency Load Current
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FIGURE Maximum Output Current Output Voltage (Adjust RFB2 Different Output Voltage) When Input Voltage
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LM2611
Application Circuits
(Continued) Inverting Converter
Inverting Converter
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FIGURE Maximum Output Current Output Voltage (Adjust RFB2 Different Output Voltage) When Input Voltage
FIGURE Maximum Output Current Output Voltage (Adjust RFB2 Different Output Voltage) When Input Voltage
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LM2611
Application Circuits
(Continued)
20018114
FIGURE LM2611 Operating with Separate Power Biasing Supplies Split Supply Operation LM2611 operated with separate power bias supplies. circuit shown Figure power supply that regulated voltage derived from, current supply used bias LM2611. Conditions supplies are: 2.7V IVOUTI) input voltage increases, maximum output current capacbility increases. Using separate, higher voltage supply power conversion enables LM2611 provide higher output currents than would with single supply that limited voltage VIN(MAX). Shutdown/Soft Start soft start circuit used switching power supplies limit input inrush current upon start-up. Without soft-start circuit, inrush current several times steadystate load current, thus apply unnecessary stress input source. LM2611 does have soft-start circuitry, implementing circuit Figure will lower peak inrush current. SHDN coupled output through CSS. LM2611 toggled between shutdown states while output slowly decreases steadystate value. energy required reach steady-state spread over longer time input current spikes decrease (see Figure Figure 15).
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LM2611
Application Circuits
(Continued)
20018125
FIGURE LM2611 Soft Start Circuit
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FIGURE Start-Up Waveforms with Soft Start Circuit
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FIGURE Start-Up Waveforms without Soft Start Circuit
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LM2611
Application Circuits
(Continued)
High Duty Cycle/Load Current Operation circuit Figure used high duty cycles 0.5) high load currents. duty cycle will begin increase beyond input voltage drops below absolute
magnitude output voltage. RFB3 CFF2 added feedback network introduce frequency compensation (pole-zero pair) necessary stabilize circuit under combination high duty cycle high load currents.
20018129
FIGURE LM2611 High Current Schematic
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LM2611 1.4MHz Converter
Physical Dimensions
unless otherwise noted
inches (millimeters)
5-lead SOT-23 Package Package Number MF05A
National does assume responsibility circuitry described, circuit patent licenses implied National reserves right time without notice change said circuitry specifications. most current product information visit www.national.com. LIFE SUPPORT POLICY NATIONAL'S PRODUCTS AUTHORIZED CRITICAL COMPONENTS LIFE SUPPORT DEVICES SYSTEMS WITHOUT EXPRESS WRITTEN APPROVAL PRESIDENT GENERAL COUNSEL NATIONAL SEMICONDUCTOR CORPORATION. used herein: Life support devices systems devices systems which, intended surgical implant into body, support sustain life, whose failure perform when properly used accordance with instructions provided labeling, reasonably expected result significant injury user. BANNED SUBSTANCE COMPLIANCE National Semiconductor certifies that products packing materials meet provisions Customer Products Stewardship Specification (CSP-9-111C2) Banned Substances Materials Interest Specification (CSP-9-111S2) contain ``Banned Substances'' defined CSP-9-111S2.
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LM2611 1.4MHz Converter LM2611 current mode, inverting switching

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