LM2621 Input Voltage, Step-Up DC-DC Converter LM2621 high efficie

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LM2621 Input Voltage, Step-Up DC-DC Converter LM2621 high efficie

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LM2621 Input Voltage, Step-Up DC-DC Converter
LM2621 Input Voltage, Step-Up DC-DC Converter
LM2621 high efficiency, step-up DC-DC switching regulator battery-powered input voltage systems. accepts input voltage between 1.2V converts into regulated output voltage. output voltage adjusted between 1.24V 14V. internal 0.17 N-Channel MOSFET power switch. Efficiencies achievable using LM2621. high switching frequency (adjustable 2MHz) LM2621 allows tiny surface mount inductors capacitors. Because unique constant-duty-cycle gated oscillator topology very high efficiencies realized over wide load range. supply current reduced 80µA because BiCMOS process technology. shutdown mode, supply current less than 2.5µA. LM2621 available Mini-SO-8 package. This package uses half board area standard 8-pin height just 1.09 1.09 Package Height Switching Frequency 1.2V Input Voltage 1.24V Adjustable Output Voltage Load Current 0.17 Internal MOSFET Regulator Efficiency Typical Operating Current 2.5µA Guaranteed Supply Current Shutdown
Applications
PDAs, Cellular Phones 2-Cell 3-Cell Battery-Operated Equipment PCMCIA Cards, Memory Cards Flash Memory Programming TFT/LCD Applications 3.3V 5.0V Conversion Devices Two-Way Pagers Palmtop Computers Hand-Held Instruments
Features
Small Mini-SO8 Package (Half Footprint Standard 8-Pin Package)
Typical Application Circuit
10093412
2005 National Semiconductor Corporation
DS100934
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LM2621
Connection Diagram
Mini SO-8 (MM) Package
10093418
View
Ordering Information
Order Number LM2621MMX LM2621MM Package Type Mini SO-8 Mini SO-8 Package Drawing MUA08A MUA08A Package Marking S06A S06A Supplied 3000 Units Tape Reel 1000 Units Tape Reel
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LM2621
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 (TA=25°C) (Note Rating (Note
500mW
Operating Conditions (Note
Pins BOOT Ambient Temperature (TA) 2.5V -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: VDD= VOUT= 3.3V. Symbol VIN_ST VIN_OP VOUT_MAX VHYST Parameter Minimum Start-Up Supply Voltage (Note Minimum Operating Supply Voltage (once started) Voltage Maximum Output Voltage Hysteresis Voltage (Note 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 MOSFET Switch Resistance Voltage (Note Voltage High (Note 0.7VDD 1.3V; VDD, BOOT Pins 5.0V; 200mV Condition ILOAD ILOAD 0.65 1.24 0.01 2.85 0.17 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 Output regulation, VOUT VOUT (NOMINAL) Note This hysteresis value internal comparator used gated-oscillator control scheme. 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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LM2621
Description
FREQ SGND BOOT Name PGND Power Ground Active-Low Shutdown Input Frequency Adjust. external resistor connected between this (VDD) sets switching frequency LM2621. Output Voltage Feedback Signal Ground Power Supply Internal Circuitry Bootstrap Supply Gate Drive Internal MOSFET Power Switch Drain Internal MOSFET Power Switch Function
Typical Performance Characteristics
Efficiency Load Current VOUT 5.0V Efficiency Load Current VOUT 3.3V
10093401
10093402
Temperature Temperature
10093403
10093404
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LM2621
Typical Performance Characteristics
Temperature
(Continued)
10093405
10093406
VIN_ST Load Current VOUT 3.3V
10093407
10093408
Switching Frequency
Peak Inductor Current Load Current
10093410 10093409
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LM2621
Typical Performance Characteristics
Maximum Load Current Input Voltage
(Continued)
10093411
Detailed Description
OPERATING PRINCIPLE LM2621 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 switching DC-DC regulator boosts input voltage between 1.2V regulated output voltage between 1.24V
14V. LM2621 starts from 1.1V input remains operational down 0.65V. 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.
10093414
FIGURE Functional Diagram
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LM2621
Detailed Description
(Continued)
GATED OSCILLATOR CONTROL SCHEME unique gated oscillator control scheme enables LM2621 have ultra-low quiescent current provides high efficiency over wide load range. switching frequency internal oscillator programmable using external resistor between MHz. This control scheme uses hysteresis window regulate output voltage. When output voltage below upper threshold window, LM2621 switches continuously with fixed duty cycle switching frequency selected user. During first part each switching cycle, internal N-channel MOSFET switch turned This causes current ramp inductor store energy. During second part each switching
cycle, MOSFET turned off. voltage across inductor reverses forces current through diode output filter capacitor load. Thus when LM2621 switches continuously, output voltage starts ramp When output voltage hits upper threshold window, LM2621 stops switching completely. This causes output voltage droop because energy stored output capacitor depleted load. When output voltage hits lower threshold hysteresis window, LM2621 starts switching continuously again causing output voltage ramp towards upper threshold. Figure shows switch voltage output voltage waveforms. Because this type control scheme, quiescent current inherently very low. light loads gated oscillator control scheme offers much higher efficiency compared conventional control scheme.
10093415
FIGURE Typical Step-Up Regulator Waveforms VOLTAGE START-UP LM2621 start-up from input voltages 1.1V. start-up, control circuitry switches N-channel MOSFET continuously duty cycle until output voltage reaches 2.5V. After this output voltage reached, normal step-up regulator feedback gated oscillator control scheme take over. Once device regulation operate down 0.65V input, since internal power boot-strapped from output using pin. SHUTDOWN LM2621 features shutdown mode that reduces quiescent current less than guaranteed 2.5µA 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 (Pin When logic input this pulled below 0.15VDD, device goes into shutdown mode. logic input this should above 0.7VDD device work normal step-up mode. OUTPUT VOLTAGE RIPPLE FREQUENCY major component output voltage ripple hysteresis used gated oscillator control scheme. frequency this voltage ripple proportional load current. frequency this ripple does necessitate larger inductors capacitors however, since size these components determined switching frequency oscillator which upto 2MHz using external resistor. 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 circuitry 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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LM2621
Design Procedure
SETTING OUTPUT VOLTAGE output voltage step-up regulator between 1.24V connecting feedback resistive divider made RF2. resistor values selected follows: /[(VOUT/ 1.24) value 150k suggested RF1. Then, selected using above equation. 39pF capacitor (CF1) connected across helps feeding back most ripple VOUT pin. This helps reduce peak-topeak output voltage ripple well improve efficiency step-up regulator, because hysteresis 30mV used gated oscillator control scheme. BOOTSTRAPPING When output voltage (VOUT) between 2.5V 5.0V bootstrapped operation suggested. This achieved connecting (Pin VOUT. However VOUT outside this range, should connected voltage source whose range between 2.5V This input voltage (VIN), VOUT stepped down using linear regulator, different voltage source available system. This referred non-bootstrapped operation. maximum acceptable voltage BOOT (Pin 10V. SETTING SWITCHING FREQUENCY switching frequency oscillator selected choosing external resistor (RFQ) connected between FREQ pins. graph titled ,,Switching Frequency 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.
INDUCTOR SELECTION LM2621's high switching frequency enables small surface mount inductor. 6.8µH shielded inductor suggested. inductor should have saturation current rating higher than peak current will experience during circuit operation (see graph titled ,,Peak Inductor Current Load Current" Typical Performance Characteristics section). Less than 100m suggested high efficiency. Open-core inductors cause flux linkage with circuit components interfere with normal operation circuit. They should avoided. high efficiency, choose inductor with high frequency core material, such ferrite, reduce core losses. minimize radiated noise, toroid, core shielded core inductor. inductor should connected close possible. Table list inductor manufacturers. OUTPUT DIODE SELECTION Schottky diode should used output diode. forward current rating diode should higher than load 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. INPUT OUTPUT FILTER CAPACITORS SELECTION Tantalum chip capacitors recommended input output filter capacitors. 22µF capacitor suggested input filter capacitor. should have working voltage rating higher than maximum input voltage. 68µF tantalum capacitor suggested output capacitor. working voltage rating should greater than output voltage. Very high values should avoided. Table shows list capacitor manufacturers.
TABLE 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 output filter capacitors PGND SGND pins LM2621 should connected using short, direct wide traces. voltage feedback network (RF1, RF2, CF1) should kept very close pin. Noisy traces, such from pin, should kept away from pins. traces that between Vout should kept away from inductor flux. Always provide sufficient copper area dissipate heat power loss circuitry prevent thermal protection circuitry from shutting down.
BOARD LAYOUT High switching frequencies high peak currents make proper layout board important part design. Poor design cause excessive ground-bounce, both which cause malfunction loss regulation corrupting voltage feedback signal injecting noise into control section. Power components such inductor, input output filter capacitors, output diode should placed close regulator possible, their traces should kept short, direct wide. ground pins input
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LM2621
Application examples
EXAMPLE 5V/0.5A Step-Up Regulator
10093412
National Vishay/Sprague Vishay/Sprague Motorola Coilcraft
LM2621MM 595D226X06R3B2T, Tantalum 595D686X0010C2T, Tantalum MBRS140T3 DT1608C-682
EXAMPLE Tall 5V/0.2A Step-Up Regulator Profile Applications
10093417
National Vishay/Sprague Vishay/Sprague Motorola Vishay/Dale
LM2621MM 592D156X06R3B2T, Tantalum 592D336X06R3C2T, Tantalum MBRS140T3 ILS-3825-03
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LM2621
EXAMPLE 3.3V/0.5A SEPIC Regulator
10093422
National Vishay/Sprague Vishay/Sprague Motorola Coilcraft Vishay/Vitramon
LM2621MM 595D226X06R3B2T, Tantalum 595D686X0010C2T, Tantalum MBRS140T3 DT1608C-682 VJ1210Y105M Ceramic
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LM2621 Input Voltage, Step-Up DC-DC Converter
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.
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 manufactures products uses packing materials that 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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LM2621 Input Voltage, Step-Up DC-DC Converter LM2621 high efficie

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