DESCRIPTION August 1999 from Single Li-Ion Cell 800mA SEPIC
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LT1308A/LT1308B High Current, Micropower Single Cell, 600kHz DC/DC Converters
DESCRIPTION
August 1999
from Single Li-Ion Cell 800mA SEPIC Mode from Four NiCd Cells Fixed Frequency Operation: 600kHz Boost Converter Outputs Starts into Heavy Loads Automatic Burst ModeOperation Light Load (LT1308A) Continuous Switching Light Loads (LT1308B) VCESAT Switch: 300mV Pin-for-Pin Upgrade Compatible with LT1308 Lower Quiescent Current Shutdown: (Max) Improved Accuracy Low-Battery Detector Reference: 200mV
®1308A/LT1308B micropower, fixed frequency step-up DC/DC converters that operate over input voltage range. They improved versions LT1308 recommended designs. LT1308A features automatic shifting power saving Burst Mode operation light loads consumes just 140µA load. LT1308B features continuous switching light loads operates quiescent current 2.5mA. Both devices consume less than shutdown. Low-battery detector accuracy significantly tighter than LT1308. 200mV reference specified room over temperature. shutdown enables device when tied higher source does need tied LT1308. internal clamp results improved transient response switch voltage rating been increased 36V, enabling higher output voltage applications. LT1308A/LT1308B available 8-lead 14-lead TSSOP packages.
registered trademarks Linear Technology Corporation. Burst Mode trademark Linear Technology Corporation.
APPLICATIONS
GSM/CDMA Phones Digital Cameras Bias Supplies Answer-Back Pagers Receivers Battery Backup Supplies Handheld Computers
TYPICAL APPLICATION
4.7µH LT1308B SHDN 100pF TAJC476M010 TPSD227M006 10BQ015 MURATA LQH6N4R7 *R1: 169k VOUT 3.3V 887k VOUT 100k 309k
EFFICIENCY
Converter Efficiency
3.6V 4.2V
Li-Ion CELL
47µF SHUTDOWN
220µF
1.5V
1308A/B
LOAD CURRENT (mA) 1000
1308A/B F01a
Figure LT1308B Single Li-Ion Cell 5V/1A DC/DC Converter
Information furnished Linear Technology Corporation believed accurate reliable. However, responsibility assumed use. Linear Technology Corporation makes representation that interconnection circuits described herein will infringe existing patent rights.
2.5V
LT1308A/LT1308B ABSOLUTE RATI
VIN, SHDN, Voltage Voltage 0.4V Voltage Voltage Voltage 0.1V Current into ±1mA
PACKAGE/ORDER ATIO
VIEW SHDN
ORDER PART NUMBER LT1308ACF LT1308BCF
SHDN
PACKAGE 14-LEAD PLASTIC TSSOP
(Note TJMAX 125°C, 80°C/W
Consult factory Military grade parts.
ELECTRICAL CHARACTERISTICS
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. Commercial Grade 70°C. 1.1V, VSHDN VIN, unless otherwise noted.
SYMBOL PARAMETER Quiescent Current CONDITIONS Switching, LT1308A Switching, LT1308B VSHDN (LT1308A/LT1308B)
Feedback Voltage Bias Current Reference Line Regulation Minimum Input Voltage (Note 1.1V 1.2V Duty Cyle (Note (25°C, 0°C), 1.5V (70°C), 1.5V 2.5V, Circuit Figure
fOSC
Error Transconductance Error Voltage Gain Switching Frequency Maximum Duty Cycle Switch Current Limit Switch VCESAT Burst Mode Operation Switch Current Limit (LT1308A)
(Note
Operating Temperature Range Commercial 70°C Extended Commerial (Note 40°C 85°C Industrial 40°C 85°C Storage Temperature Range 65°C 150°C Lead Temperature (Soldering, sec). 300°C
VIEW
ORDER PART NUMBER LT1308ACS8 LT1308AIS8 LT1308BCS8 LT1308BIS8 PART MARKING 1308A 1308AI 1308B 1308BI
PACKAGE 8-LEAD PLASTIC TJMAX 125°C, 80°C/W
0.01
1.24
UNITS µmhos
1.20
1.22 0.03 0.01 0.92
LT1308A/LT1308B
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. Commercial Grade 70°C. 1.1V, VSHDN VIN, unless otherwise noted.
SYMBOL PARAMETER Shutdown Current CONDITIONS VSHDN 1.1V VSHDN VSHDN
ELECTRICAL CHARACTERISTICS
0.01
0.25
UNITS
Threshold Voltage Output Leakage Current Input Bias Current (Note Low-Battery Detector Gain Switch Leakage Current
0.01 3000 0.01
ISINK 50µA VLBI 250mV, VLBO VLBI 150mV
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. Industrial Grade 40°C 85°C. 1.2V, VSHDN VIN, unless otherwise noted.
SYMBOL PARAMETER Quiescent Current CONDITIONS Switching, LT1308A Switching, LT1308B VSHDN (LT1308A/LT1308B) (Note 1.1V
0.01
1.25
UNITS µmhos
Feedback Voltage Bias Current Reference Line Regulation Minimum Input Voltage
1.19
1.22 0.05 0.01 0.92
fOSC
Error Transconductance Error Voltage Gain Switching Frequency Maximum Duty Cycle Switch Current Limit Switch VCESAT Burst Mode Operation Switch Current Limit (LT1308A) Shutdown Current
Duty Cyle (Note (25°C, 40°C), 1.5V (85°C), 1.5V 2.5V, Circuit Figure VSHDN 1.1V VSHDN VSHDN
0.01 0.01 3000
0.25
Threshold Voltage
Output Leakage Current Input Bias Current (Note Low-Battery Detector Gain Switch Leakage Current
ISINK 50µA VLBI 250mV, VLBO VLBI 150mV
0.01
LT1308A/LT1308B
ELECTRICAL CHARACTERISTICS
Note Absolute Maximum Ratings those values beyond which life device impaired. Note LT1308ACS8 LT1308BCS8 designed, characterized expected meet industrial temperature limits, tested -40°C 85°C. grade devices guaranteed. Note Bias current flows into pin. Note Switch current limit guaranteed design and/or correlation static tests. Duty cycle affects current limit ramp generator (see Block Diagram). Note Bias current flows pin. Note Connect four pins (Pins 4-7) together device. Similarly, connect three pins (Pins 8-10) together pins (Pins together device.
TYPICAL PERFORMANCE CHARACTERISTICS
LT1308B 3.3V Output Efficiency
EFFICIENCY
1.8V
2.5V
EFFICIENCY
1.2V
EFFICIENCY
LOAD CURRENT (mA)
LT1308B Output Efficiency
3.3V
SWITCH VCESAT (mV)
EFFICIENCY
LOAD CURRENT (mA) 1000
1308A/B
1308A/B
LT1308A 3.3V Output Efficiency
1000 LOAD CURRENT (mA) 1000
1308A/B
LT1308A Output Efficiency
4.2V 3.6V
1.8V
2.5V
1.2V
1.5V
2.5V
LOAD CURRENT (mA)
1000
1308A/B
LT1308A Transient Response Circuit Figure
Switch Saturation Voltage Current
VOUT 100mV/DIV COUPLED ILOAD 3.6V VOUT COUT 220µF 100µs/DIV
1308
85°C 25°C -40°C
SWITCH CURRENT
1308
LT1308A/LT1308B
FUNCTIONS
(Pin Compensation Error Amplifier. Connect series from this ground. Typical values 100pF. Minimize trace area (Pin Feedback Pin. Reference voltage 1.22V. Connect resistive divider here. Minimize trace area VOUT according VOUT 1.22V(1 R1/R2). SHDN (Pin Shutdown. Ground this turn switcher. enable, more. SHDN does need enable device. (Pin Ground. Connect directly local ground plane. Ground plane should enclose components associated with LT1308. copper connected also functions heat sink. Maximize this area keep chip heating minimum. (Pin Switch Pin. Connect inductor/diode here. Minimize trace area this keep down. (Pin Supply Pin. Must have local bypass capacitor right pin, connected directly ground. (Pin Low-Battery Detector Input. 200mV reference. Voltage must stay between -100mV Low-battery detector does function with SHDN grounded. used, float pin. (Pin Low-Battery Detector Output. Open collector, sink 50µA. pull-up recommended. high impedance when SHDN grounded.
BLOCK DIAGRAM
VOUT (EXTERNAL) (EXTERNAL)
140k
RAMP GENERATOR
600kHz OSCILLATOR *HYSTERESIS LT1308A ONLY
Figure LT1308A/LT1308B Block Diagram
2VBE SHDN
ERROR AMPLIFIER BIAS
SHUTDOWN
ENABLE 200mV
COMPARATOR
DRIVER
0.03
1308
LT1308A/LT1308B
APPLICATIONS INFORMATION
OPERATION LT1308A combines current mode, fixed frequency architecture with Burst Mode micropower operation maintain high efficiency light loads. Operation best understood referring block diagram Figure form bandgap reference core whose loop closed around output converter. When feedback voltage 1.22V, along with 80mV drop across forward biases Q2's base collector junctions 300mV. Because this enough saturate either transistor, higher voltage than VIN. When there load, rises slightly above 1.22V, causing (the error amplifier's output) decrease. When reaches bias voltage hysteretic comparator A1's output goes low, turning circuitry except input stage, error amplifier lowbattery detector. Total current consumption this state 120µA. output loading causes voltage decrease, A1's output goes high, enabling rest Switch current limited approximately 400mA initially after A1's output goes high. load light, output voltage (and voltage) will increase until A1's output goes low, turning rest LT1308A. frequency ripple voltage appears output. ripple frequency dependent load current output capacitance. This Burst Mode operation keeps output regulated reduces average current into resulting high efficiency even load currents less. output load increases sufficiently, A1's output remains high, resulting continuous operation. When LT1308A running continuously, peak switch current controlled regulate output voltage. switch turned beginning each switch cycle. When summation signal representing switch current ramp generator (introduced avoid subharmonic oscillations duty factors greater than 50%) exceeds signal, comparator changes state, resetting flip-flop turning switch. Output voltage increases switch current increased. output, attenuated resistor divider, appears pin, closing overall loop. Frequency compensation provided external series network connected between ground. Low-battery detector A4's open-collector output (LBO) pulls when voltage drops below 200mV. There hysteresis allowing used amplifier some applications. entire device disabled when SHDN brought low. enable converter, SHDN must greater. need tied LT1308. LT1308B differs from LT1308A that there hysteresis comparator Also, bias point lower than LT1308B that switching occur inductor current less than 100mA. Because hysteresis, there Burst Mode operation light loads device continues switching constant frequency. This results absence frequency output voltage ripple expense efficiency. difference between devices clearly illustrated Figure traces Figure shows LT1308A/LT1308B circuit, using components indicated Figure output. Input voltage Load current stepped from 50mA 800mA both circuits. frequency Burst Mode operation voltage ripple observed Trace while none observed Trace light loads, LT1308B will begin skip alternate cycles. load point which this occurs decreased increasing inductor value. However, output ripple will continue significantly less than LT1308A output ripple. Further, LT1308B forced into micropower mode, where falls from 200µA sinking 40µA more pin. This stops switching causing A1's output low.
TRACE LT1308A VOUT, 100mV/DIV COUPLED TRACE LT1308B VOUT, 100mV/DIV COUPLED 800mA ILOAD 50mA 200µs/DIV (CIRCUIT FIGURE
1308
Figure LT1308A Exhibits Burst Mode Operation Output Voltage Ripple 50mA Load, LT1308B Does
LT1308A/LT1308B
APPLICATIONS INFORMATION
LAYOUT HINTS LT1308A/LT1308B switch current high speed, mandating careful attention layout proper performance. will advertised performance with careless layouts. Figure shows recommended component placement boost (step-up) converter. Follow this closely your layout. Note direct path switching loops. Input capacitor must placed close 5mm) package. little 10mm wire trace from will cause problems such inability regulate oscillation. negative terminal output capacitor should close LT1308A/LT1308B. Doing this reduces dI/dt ground copper which keeps high frequency spikes minimum. DC/DC converter ground should board ground plane place only, avoid introducing dI/dt ground plane. SEPIC (Single-Ended Primary Inductance Converter) schematic shown Figure This converter topology produces regulated output over input voltage range that spans (i.e., higher lower than) output. Recommended component placement SEPIC shown Figure COMPONENT SELECTION Inductors Suitable inductors with LT1308A/LT1308B must fulfill requirements. First, inductor must able handle current steady-state, well support transient start-up current over without inductance decreasing more than 60%. Second, inductor should have DCR, under 0.05 that copper loss minimized. Acceptable inductance values range between 20µH, with 4.7µH best most applications. Lower value inductors physically smaller than higher value inductors same current capability. Table lists some inductors have found perform well LT1308A/LT1308B application circuits. This exclusive list.
Table
VENDOR Murata Sumida Coiltronics PART LQH6C4R7 CDRH734R7 CTX5-1 VALUE 4.7µH 4.7µH PHONE 770-436-1300 847-956-0666 561-241-7876
Capacitors Equivalent Series Resistance (ESR) main issue regarding selection capacitors, especially output capacitors. output capacitors specified with LT1308A/ LT1308B circuits have specifically designed power supply applications. Output voltage ripple boost converter equal multiplied switch current. performance TPSD227M006 220µF tantalum evaluated referring Figure When load 800mA, peak switch current approximately Output voltage ripple about 60mVPP, output capacitor 60mV/2A 0.03. Ripple further reduced paralleling ceramic units. Table lists some capacitors have found perform well LT1308A/LT1308B application circuits. This exclusive list.
Table
VENDOR Taiyo Yuden Taiyo Yuden SERIES PART TPSD227M006 TPSD107M010 LMK432BJ226 TMK432BJ106 VALUE 220µF, PHONE 803-448-9411
100µF, 803-448-9411 22µF, 10µF, 408-573-4150 408-573-4150
Diodes have found Motorola MBRS130 International Rectifier 10BQ015 perform well. applications where VOUT exceeds 30V, diodes such MBRS140 10BQ040.
LT1308A/LT1308B
APPLICATIONS INFORMATION
GROUND PLANE CTX10-2 4.7µF CERAMIC
SHUTDOWN
LT1308A LT1308B
MULTIPLE VIAs
VOUT
Figure Recommended Component Placement Boost Converter. Note Direct High Current Paths Using Wide Traces. Minimize Trace Area (VC) (FB). Multiple Vias Copper Ground Plane. Vias Location Only Avoid Introducing Switching Currents into Ground Plane
GROUND PLANE
SHUTDOWN
LT1308A LT1308B
MULTIPLE VIAs
Figure Recommended Component Placement SEPIC
47µF SHUTDOWN LT1308B SHDN 680pF
309k 100k VOUT 500mA
220µF 6.3V
TAJC476M016 TAIYO YUDEN EMK325BJ475(X5R) TPSD227M006
10BQ015 COILTRONICS CTX10-2
1308A/B
1308
Figure SEPIC (Single-Ended Primary Inductance Converter) Converts Input 5V/500mA Regulated Output
VOUT
1308
LT1308A/LT1308B
APPLICATIONS INFORMATION
SHDN LT1308A/LT1308B SHDN improved over LT1308. does require tying enable device, needs only logic level signal. voltage SHDN vary from independent VIN. Further, floating this same effect grounding, which shut device down, reducing current drain less. LOW-BATTERY DETECTOR low-battery detector LT1308A/LT1308B features improved accuracy drive capability compared LT1308. 200mV reference accuracy open-collector output sink 50µA. LT1308A/ LT1308B low-battery detector simple input gain stage with open-collector output. negative input gain stage tied internally 200mV reference. positive input pin. Arrangement low-battery detector straightforward. Figure details hookup. need only enough value that bias current doesn't cause large errors. 100k adequate. 200mV reference also accessed shown Figure cross plot low-battery detector shown Figure swept with input which varies from 195mV 205mV, with 100k pull-up resistor, displayed. START-UP LT1308A/LT1308B start into heavy loads, unlike many CMOS DC/DC converters that derive operating voltage from output technique known "bootstrapping"). Figure details start-up waveforms Figure circuit with load 1.5V. Inductor current rises 3.5A output capacitor charged. After output reaches inductor current about Figure load input voltage Output voltage reaches 500µs after device enabled. Figure shows start-up behavior Figure SEPIC circuit, driven from input with load. output reaches about after device enabled. CDMA PHONES LT1308A/LT1308B suitable converting single Li-Ion cell powering power stages CDMA phones. Improvements LT1308A/LT1308B error amplifiers allow external compensation values reduced, resulting faster transient response compared LT1308. circuit Figure (same Figure printed again convenience) provides output from Li-Ion cell. Figure details transient response LT1308A operating 4.2V, 3.6V Ripple voltage Burst Mode operation seen 10mA load. Figure shows transient response LT1308B under same conditions. Note lack Burst Mode ripple 10mA load.
100k LT1308A LT1308B
200mV INTERNAL REFERENCE
100k 200k PROCESSOR VBAT VREF 200mV 200mV 2N3906 LT1308A LT1308B
1308
VBAT
1308
Figure Setting Low-Battery Detector Trip Point
10µF
Figure Accessing 200mV Reference
LT1308A/LT1308B
APPLICATIONS INFORMATION
VOUT 1V/DIV VLBO 1V/DIV
VLBI (mV)
1308
Figure Low-Battery Detector Input/Output Characteristic
VOUT 2V/DIV
1A/DIV VSHDN 5V/DIV 1ms/DIV
1308
Figure Boost Converter Figure Start-Up from 1.5V Input into Load
Li-Ion CELL
47µF SHUTDOWN
TAJC476M010 TPSD227M006
Figure Li-Ion Boost Converter Delivers
2A/DIV VSHDN 5V/DIV 500µs/DIV
1308
Figure Boost Converter Figure Start-Up from Input into Load
VOUT 2V/DIV
2A/DIV VSHDN 5V/DIV 500µs/DIV
1308
Figure SEPIC Start-Up from Input into Load
4.7µH
309k
LT1308B SHDN 100pF
100k
220µF
10BQ015 MURATA LQH6N4R7
1308A/B
LT1308A/LT1308B
APPLICATIONS INFORMATION
VOUT 4.2V VOUT 3.6V VOUT ILOAD 10mA VOUT 4.2V VOUT 3.6V VOUT ILOAD 10mA
1308
VOUT TRACES 200mV/DIV
200µs/DIV
Figure LT1308A Li-Ion Boost Converter Transient Response Load Step
PACKAGE DESCRIPTION
Dimensions inches (millimeters) unless otherwise noted. Package 14-Lead Plastic TSSOP (4.4mm)
(LTC 05-08-1650)
4.90 5.10* (0.193 0.201)
4.30 4.48** (0.169 0.176)
0.09 0.18 (0.0035 0.0071)
0.50 0.70 (0.020 0.028)
NOTE: DIMENSIONS MILLIMETERS *DIMENSIONS INCLUDE MOLD FLASH. MOLD FLASH SHALL EXCEED 0.152mm (0.006") SIDE **DIMENSIONS INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL EXCEED 0.254mm (0.010") SIDE
VOUT TRACES 200mV/DIV
100µs/DIV
1308
Figure LT1308B Li-Ion Boost Converter Transient Response Load Step
6.25 6.50 (0.246 0.256)
1.10 (0.0433)
0.65 (0.0256) 0.18 0.30 (0.0071 0.0118)
0.05 0.15 (0.002 0.006)
TSSOP 1299
LT1308A/LT1308B
TYPICAL APPLICATION
SEPIC Converts Input 5V/500mA Regulated Output
CTX10-2 4.7µF CERAMIC
47µF SHUTDOWN LT1308B SHDN 680pF
309k 100k VOUT 500mA
TAJC476M016 TAIYO YUDEN EMK325BJ475(X5R) TPSD227M006
10BQ015 COILTRONICS CTX10-2
PACKAGE DESCRIPTION
0.010 0.020 (0.254 0.508) 0.008 0.010 (0.203 0.254)
0.014 0.019 (0.355 0.483) *DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH SHALL EXCEED 0.006" (0.152mm) SIDE **DIMENSION DOES INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL EXCEED 0.010" (0.254mm) SIDE
0.016 0.050 (0.406 1.270)
RELATED PARTS
PART NUMBER LT1302 LT1304 LT1316 1474 LTC1516 LTC1522 LT1610 LT1611 LT1613 LT1615 LTC1682 LT1949
DESCRIPTION High Output Current Micropower DC/DC Converter 2-Cell Micropower DC/DC Converter Burst Mode Operation DC/DC with Programmable Current Limit Micropower Step-Down DC/DC Converter 2-Cell Regulated Charge Pump Micropower, Charge Pump DC/DC Converter Single-Cell Micropower DC/DC Converter Inverting 1.4MHz Switching Regulator 5-Lead SOT-23 1.4MHz Switching Regulator 5-Lead SOT-23 Micropower Step-Up DC/DC 5-Lead SOT-23 Doubler Charge Pump with Noise 600kHz, Switch DC/DC Converter
LT1307/LT1307B Single Cell, Micropower, 600kHz DC/DC Converters LT1317/LT1317B Micropower, 600kHz DC/DC Converters
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, 95035-7417
(408)432-1900 FAX: (408) 434-0507 www.linear-tech.com
3.3V 12V/300mA Step-Up DC/DC Converter
4.7µH
300mA 887k
Li-Ion CELL
47µF SHUTDOWN LT1308B SHDN 100pF
100k
100µF
220µF 6.3V
1308A/B
TAJC476M010 TPSD107M016 10BQ015
MURATA LQH6N4R7
1308A/B TA01
Dimensions inches (millimeters) unless otherwise noted.
Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC 05-08-1610)
0.053 0.069 (1.346 1.752) 0.004 0.010 (0.101 0.254) 0.228 0.244 (5.791 6.197) 0.150 0.157** (3.810 3.988) 0.189 0.197* (4.801 5.004)
0.050 (1.270)
1298
COMMENTS 5V/600mA from Internal Switch, 200µA 5V/200mA, Low-Battery Detector Active Shutdown 3.3V 75mA from Cell, MSOP Package 1.5V Minimum, Precise Control Peak Current Limit 100µA Operate with 1.5V Efficiency, 10µA 250mA 12µA Inudctors, 50mA from Input Regulated Output, 20mA from Input 30mA from 1.7MHz Fixed Frequency 150mA from Input, Tiny SOT-23 package 200mA from 4.4V Input, Tiny SOT-23 package 20µA 36V, 350mA Switch Adjustable Fixed 3.3V, Outputs, 60µVRMS Output Noise 1.1A, 0.5, Internal Switch, 1.5V
1308abis, sn1308ab LT/TP 0899 PRINTED
LINEAR TECHNOLOGY CORPORATION 1999
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