LM2623 Ratio Adaptive Gated Oscillator Based, Boost Converter-Low Vin,

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LM2623 Ratio Adaptive Gated Oscillator Based, Boost Converter-Low Vin,

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LM2623 Ratio Adaptive Gated (RAG) Oscillator Based, Converter Vin, Ripple, General Purpose, High Efficiency, Boost
LM2623 Ratio Adaptive Gated Oscillator Based, Boost Converter-Low Vin, Ripple, General Purpose
LM2623 high efficiency, general purpose, step-up DC-DC switching regulator battery-powered input voltage systems. accepts input voltage between volts converts into regulated output voltage. LM2623 used generate volts using inductor almost positive voltage using transformer. internal N-Channel MOSFET power switch. Efficiencies achievable with LM2623. order adapt number applications, LM2623 allows designer vary output voltage, operating frequency (300kHz MHz) duty cycle (17% 90%) optimize part's performance. selected values fixed vary with battery voltage input output voltage ratio. Using these techniques according design guidelines improve efficiency reduce parts cost both. LM2623 gated oscillator uses very simple, on/off regulation mode produce good efficiency stable operation over wide operating range. normally regulates skipping switching cycles when reaches regulation limit (Pulse Frequency Modulation). some applications, with proper selection external feedback components, also regulate cycle cycle, similar Pulse Width Modulated parts. does this adjusting time between switching cycles, while maintaining continuous current through coil. This cycle cycle type results very ripple output voltage and/or minimum sized output capacitors, similar parts.This mode also typically maximizes efficiency.
Features
Good Efficiency Over Very Wide Load Range Very Output Voltage Ripple Small, Mini-SO-8 Package (Half Footprint Standard Package) 1.09 Package Height Switching Frequency Operating Voltage 1.1V Start-up Voltage 1.24V Adjustable Output Voltage Load Current 0.17 Internal MOSFET Regulator Efficiency Typical Operating Current (into supply) 2.5µA Guaranteed Supply Current Shutdown
Applications
Cameras, Pagers Cell Phones PDAs,Palmtop Computers, devices White Drive, Scanned LCDs Flash Memory Programming Hand-Held Instruments Cell Alkaline Systems Cell Lithium-ion Systems
Typical Application Circuit
20038801
2002 National Semiconductor Corporation
DS200388
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LM2623
Connection Diagram
Mini SO-8 (MM) Package
20038818
View
Ordering Information
Order Number LM2623MMX LM2623AMMX LM2623AMM LM2623MM Package Type Mini SO-8 Mini SO-8 Mini SO-8 Mini SO-8 Package Drawing MUA08A MUA08A MUA08A MUA08A Package Marking S46B S46A S46A S46B Supplied 3000 Units Tape Reel 3000 Units Tape Reel 1000 Units Tape Reel 1000 Units Tape Reel
Description
FREQ SGND BOOT Name PGND Power Ground Active-Low Shutdown Input Frequency Adjust. external resistor connected between this voltage source sets switching frequency LM2623. Output Voltage Feedback Signal Ground Power Supply Internal Circuitry Bootstrap Supply Gate Drive Internal MOSFET Power Switch Drain Internal MOSFET Power Switch Function
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LM2623
Absolute Maximum Ratings
(Note
Military/Aerospace specified devices required, please contact National Semiconductor Sales Office/ Distributors availability specifications. Voltage BOOT, VDD, Pins FREQ (Note TJmax (Note Storage Temperature Range Lead Temp. (Soldering, sec) -0.5 14.5V -0.5V 100µA 240°C/W 150°C -65°C +150°C 260°C
Power Dissipation =25°C) (Note Rating (Note
500mW
Operating Conditions (Note
Pins BOOT Ambient Temperature (TA) -40°C +85°C
Electrical Characteristics
Limits standard typeface 25°C, limits boldface type apply over full operating temperature range -40°C +85°C. Unless otherwise specified: VOUT 3.3V. Symbol VDD_ST VIN_OP VOUT_MAX Parameter Start-Up Supply Voltage 25°C Minimum Operating Supply Voltage (once started) Voltage Maximum Output Voltage Efficiency 3.6V; VOUT ILOAD 500mA 2.5V; VOUT 3.3V; ILOAD 200mA RDS_ON Switch Duty Cycle Operating Quiescent Current (Note Shutdown Quiescent Current (Note Switch Peak Current Limit Switch Peak Current Limit MOSFET Switch Resistance Voltage (Note Voltage High (Note 0.7VDD 1.3V; VDD, BOOT Pins 5.0V; 200mV LM2623A LM2623 0.17 Condition ILOAD (Note ILOAD 0.65 1.24 0.01 0.26 1.2028 1.2772 Units
Enable Section VEN_LO VEN_HI 0.15VDD
Note Absolute maximum ratings indicate limits beyond which damage device occur. Electrical specifications apply when operating device outside rated operating conditions. Note maximum power dissipation must derated elevated temperatures dictated Tjmax (maximum junction temperature), (junction ambient thermal resistance), (ambient temperature). maximum allowable power dissipation temperature Pdmax (Tjmax TA)/ number given Absolute Maximum Ratings, whichever lower. Note human body model capacitor discharged through resistor into each pin. (SW) rating Note tied Boot pins. Frequency tied through 121K resistor. VDD_ST when startu-up occurs. voltage (usually 10-50 start-up) Note This current into pin. Note This total current into pins VDD, BOOT, FREQ. Note When below VEN_LO, regulator shut down; when above VEN_HI, regulator operating.
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LM2623
Typical Performance Characteristics
Efficiency VOUT 5.0V Temperature
20038829
20038831
Frequency
Maximum Start Voltage Temperature
20038828
20038826
Typical RDS(ON) Temperature
Typical Current Limit Temperature
20038825
20038827
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LM2623
DETAILED DESCRIPTION
Operating Principle LM2623 designed provide step-up DC-DC voltage regulation battery-powered low-input voltage systems. combines step-up switching regulator, N-channel power MOSFET, built-in current limit, thermal limit, voltage reference single 8-pin MSOP package Figure switching DC-DC regulator boosts input voltage between regulated output voltage between 1.24V 14V. LM2623 starts from 1.1V input remains operational down below .8V. This device optimized cellular phones other applications requiring small size, profile, well quiescent current maximum battery life during stand-by shutdown. high-efficiency gated-oscillator topology offers output Additional features include built-in peak switch current limit, thermal protection circuitry.
20038814
FIGURE Functional Diagram Gated Oscilaltor Control Scheme on/off regulation mode LM2623, along with ultra-low quiescent current, results good efficiency over very wide load range. internal oscillator frequency programmed using external resistor constant vary with battery voltage. Adding capacitor program frequency allows designer adjust duty cycle optimize application. Adding resistor addition capacitor allows duty cycle dynamically compensate changes input/output voltage ratio. call this Ratio Adaptive Gated Oscillator circuit. Application Notes sample application circuits. Using correct components adjust oscillator allows part with ripple high efficiency over wide range loads input/output voltages.
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LM2623
DETAILED DESCRIPTION
(Continued)
20038815
FIGURE Typical Step-Up Regulator Waveforms Pulse Frequency Modulation (PFM) Pulse Frequency Modulation typically accomplished switching continuously until voltage limit reached skipping cycles after that just maintain This results somewhat hysteretic mode operation. coil stores more energy each cycle current ramps high levels. When voltage limit reached, system usually overshoots higher voltage than required, stored energy coil (see figure system will also undershoot somewhat when starts switching again because depleted stored energy coil needs store more energy reach equilibrium with load. Larger output capacitors smaller inductors reduce ripple these situations. frequency being filtered, however, basic switching frequency. lower frequency determined load, input/output voltage circuit parameters. This mode operation useful situations where load variation significant. Power managed computer systems, instance, vary from zero full load while system this usually preferred regulation mode such systems. Cycle Cycle When load doesn't vary over wide range (like zero full load), ratio adaptive circuit techniques used achieve cycle cycle regulation lower ripple smaller output capacitors). success here matching duty cycle circuit closely what required input output voltage ratio. This ratio then needs dynamically adjusted input voltage changes (usually caused batteries running down). chosen ratio should allow most energy each switching cycle delivered load only small amount stored. When regulation limit reached, overshoot will small system will settle equilibrium point where adjusts time each switching cycle meet current requirements load. time adjustment done exceeding regulation limit during each switching cycle waiting until voltage drops below limit again start next switching cycle. current coil never goes zero like frequently does hysteretic operating mode circuits with wide load variations duty cycles that aren't matched input/output voltage ratio. Optimizing duty cycle given input/output voltages conditions done using circuit values Application Notes. Voltage Start-Up LM2623 start-up from voltages volts. start-up, control circuitry switches N-channel MOSFET continuously until output reaches volts. After this output voltage reached, normal step-up regulator feedback gated oscillator control scheme take over. Once device regulation, operate down below input, since internal power boot-strapped from output using pin. Shut Down LM2623 features shutdown mode that reduces quiescent current less than guaranteed over temperature. This extends life battery battery powered applications. During shutdown, feedback control circuitry turned off. regulator's output voltage drops diode drop below input voltage. Entry into shutdown mode controlled active-low logic input (pinh- When logic input this pulled below .15Vdd, device goes into shutdown mode. logic input this should above .7Vdd device work normal stepup mode. Internal Current Limit Thermal Protection internal cycle-by-cycle current limit serves protection feature. This high enough (2.85A typical, approximately maximum) come into effect during normal operating conditions. internal thermal protection circuit disables MOSFET power switch when junction temperature (TJ) exceeds about 160°C. switch re-enabled when drops below approximately 135°C.
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LM2623
Design Procedure
Setting Output Voltage output voltage step-up regulator connecting feedback resistive divider made RF2. resistor values selected follows: /[(VOUT/ 1.24) value 100k suggested Rf2. Then, selected using above equation. Supply supply volts recommended LM2623. This voltage bootstrapped from much lower input voltage simply connecting Vout. also another voltage system battery voltage they right voltage range. event that supply voltage ripple voltage source (less than millivolts), advisable filter clean Excessive ripple reduce efficiency. Setting Switching Frequency switching frequency oscillator selected choosing external resistor (RFQ) connected between FREQ pins. graph titled ,,Switching FreTABLE Suggested Manufacturers List Inductors Coilcraft Tel: (800) 322-2645 Fax: (708) 639-1469 Coiltronics Tel: (407) 241-7876 Fax: (407) 241-9339 Pulse Engineering Tel: (619) 674-8100 Fax: (619) 674-8262 Capacitors Sprague/ Vishay Tel: (207) 324-4140 Fax: (207) 324-7223 Kemet Tel: (864) 963-6300 Fax: (864) 963-6521 Nichicon Tel: (847) 843-7500 Fax: (847) 843-2798 Diodes Motorola Tel: (800) 521-6274 Fax: (602) 244-6609 International Rectifier (IR) Tel: (310) 322-3331 Fax: (310) 322-3332 General Semiconductor Tel: (516) 847-3222 Fax: (516) 847-3150 quency RFQ" Typical Operating Characteristics section datasheet choosing value achieve desired switching frequency. high switching frequency allows very small surface mount inductors capacitors results very small solution size. switching frequency between 300kHz 2MHz recommended. Output Diode Selection Schottky diode should used output diode. forward current rating diode should higher than peak input current, reverse voltage rating must higher than output voltage. ordinary rectifier diodes, since slow switching speeds long recovery times cause efficiency load regulation suffer. Table shows list diode manufacturers.
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LM2623 Ratio Adaptive Gated (RAG) Oscillator Based, Converter Vin, Ripple, General Purpose, High Efficiency, Boost
Physical Dimensions
unless otherwise noted
inches (millimeters)
8-Lead Mini SO-8 (MM) Package Number MUA08A Order Numbers, refer table 'Ordering Information' section this document.
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.
National Semiconductor Corporation Americas Email: support@nsc.com National Semiconductor Europe Fax: 180-530 Email: europe.support@nsc.com Deutsch Tel: 9508 6208 English Tel: 2171 Tel: 8790
critical component component life support device system whose failure perform reasonably expected cause failure life support device system, affect safety effectiveness.
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National Semiconductor Japan Ltd. Tel: 81-3-5639-7560 Fax: 81-3-5639-7507
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National does assume responsibility circuitry described, circuit patent licenses implied National reserves right time without notice change said circuitry specifications.

LM2623 Ratio Adaptive Gated Oscillator Based, Boost Converter-Low Vin,

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