®1934 micropower step-down DC/DC converter with internal 400mA power s
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LT1934/LT1934-1 Micropower Step-Down Switching Regulators ThinSOT DESCRIPTION
®1934 micropower step-down DC/DC converter with internal 400mA power switch, packaged profile (1mm) ThinSOT. With wide input range 3.2V 34V, LT1934 regulate wide variety power sources, from 4-cell alkaline batteries logic rails unregulated wall transformers lead-acid batteries. Quiescent current just zero current shutdown mode disconnects load from input source, simplifying power management battery-powered systems. Burst Mode® operation drop internal power switch result high efficiency over broad range load current. LT1934 provides 300mA output current. LT1934-1 lower current limit, allowing optimum choice external components when required output current less than 60mA. Fast current limiting protects LT1934 external components against shorted outputs, even input.
Lare registered trademarks Linear Technology Corporation. Burst Mode registered trademark Linear Technology Corporation. ThinSOT trademark Linear Technology Corporation. other trademarks property their respective owners.
Wide Input Voltage Range: 3.2V Micropower Operation: 250mA from 6.5V Input (LT1934) 60mA from 6.5V Input (LT1934-1) 3.3V 250mA from 4.5V Input (LT1934) 3.3V 60mA from 4.5V Input (LT1934-1) Shutdown Current: VCESAT Switch: 200mV 300mA Profile (1mm) SOT-23 (ThinSOTTM) (2mm 0.8mm) 6-Pin Package
APPLICATIONS
Wall Transformer Regulation Automotive Battery Regulation Standby Power Portable Products Distributed Supply Regulation Industrial Control Supplies
TYPICAL APPLICATION
3.3V Step-Down Converter
Efficiency
LT1934 VOUT VOUT 3.3V
BOOST 4.5V 2.2F LT1934 SHDN
0.22F
10pF
100F
604k
EFFICIENCY
VOUT 3.3V 250mA
SANYO 4TPB100M TAIYO YUDEN GMK325BJ225MN SEMICONDUCTOR MBR0540 CENTRAL CMDSH-3 SUMIDA CDRH4D28-470
1934 TA01
LOAD CURRENT (mA)
1934 TA02
1934fd
LT1934/LT1934-1 ABSOLUTE MAXIMUM RATINGS
(Note
Input Voltage (VIN) BOOST Voltage BOOST Above Pin. SHDN Voltage Voltage
Operating Temperature Range (Note LT1934E/LT1934E-1 40°C 85°C LT1934I/LT1934I-1 40°C 125°C Maximum Junction Temperature 125°C Storage Temperature Range.- 65°C 150°C Lead Temperature (Soldering, sec) TSOT-23 300°C
CONFIGURATION
VIEW VIEW BOOST BOOST SHDN SHDN
PACKAGE 6-LEAD PLASTIC TSOT-23 TJMAX 125°C, 250°C/ 102°C/W
PACKAGE 6-LEAD (2mm 3mm) PLASTIC 73.5°C/ 12°C/W EXPOSED (PIN GND, MUST SOLDEDED
ORDER INFORMATION
LEAD FREE FINISH LT1934ES6#PBF LT1934ES6-1#PBF LT1934IS6#PBF LT1934IS6-1#PBF LT1934IDCB#PBF LT1934EDCB#PBF LT1934IDCB-1#PBF LT1934EDCB-1#PBF LEAD BASED FINISH LT1934ES6 LT1934ES6-1 LT1934IS6 LT1934IS6-1 LT1934IDCB LT1934EDCB LT1934IDCB-1 LT1934EDCB-1 TAPE REEL LT1934ES6#TRPBF LT1934ES6-1#TRPBF LT1934IS6#TRPBF LT1934IS6-1#TRPBF LT1934IDCB#TRPBF LT1934EDCB#TRPBF LT1934IDCB-1#TRPBF LT1934EDCB-1#TRPBF TAPE REEL LT1934ES6#TR LT1934ES6-1#TR LT1934IS6#TR LT1934IS6-1#TR LT1934IDCB#TR LT1934EDCB#TR LT1934IDCB-1#TR LT1934EDCB-1#TR PART MARKING* LTXP LTF8 LTAJB LTAJC LCFZ LCFZ LDHC LDHC PART MARKING* LTXP LTF8 LTAJB LTAJC LCFZ LCFZ LDHC LDHC PACKAGE DESCRIPTION 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead (2mm 3mm) Plastic 6-Lead (2mm 3mm) Plastic 6-Lead (2mm 3mm) Plastic 6-Lead (2mm 3mm) Plastic PACKAGE DESCRIPTION 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead Plastic TSOT-23 6-Lead (2mm 3mm) Plastic 6-Lead (2mm 3mm) Plastic 6-Lead (2mm 3mm) Plastic 6-Lead (2mm 3mm) Plastic TEMPERATURE RANGE -40°C 85°C -40°C 85°C -40°C 85°C -40°C 85°C -40°C 125°C -40°C 125°C -40°C 125°C -40°C 125°C TEMPERATURE RANGE -40°C 85°C -40°C 85°C -40°C 85°C -40°C 85°C -40°C 125°C -40°C 125°C -40°C 125°C -40°C 125°C
Consult Marketing parts specified with wider operating temperature ranges. *The temperature grade identified label shipping container. more information lead free part marking, http://www.linear.com/leadfree/ This product only offered trays. more information
1934fd
LT1934/LT1934-1 ELECTRICAL CHARACTERISTICS
SYMBOL Undervoltage Lockout -40°C 85°C -40°C 125°C Quiescent Current 1.3V -40°C 85°C -40°C 125°C VSHDN Comparator Trip Voltage Comparator Hysteresis Bias Current Voltage Line Regulation Switch Time Maximum Duty Cycle Switch VCESAT 1.25V -40°C 85°C -40°C 125°C -40°C 85°C -40°C 125°C Falling -40°C 85°C -40°C 125°C 1.22 1.21
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. 10V, VBOOST 15V, unless otherwise noted.
CONDITIONS 0.01 1.25 1.25 0.007 0.25 VSHDN 2.3V VSHDN 1.27 1.27 UNITS
300mA (LT1934, Package) 300mA (LT1934, Package) 75mA (LT1934-1, Package) 75mA (LT1934-1, Package) LT1934 LT1934-1 300mA (LT1934) 75mA (LT1934-1) 300mA (LT1934) 75mA (LT1934-1)
Switch Current Limit BOOST Current Minimum Boost Voltage (Note Switch Leakage Current SHDN Current SHDN Input Voltage High SHDN Input Voltage
Note Stresses beyond those listed under Absolute Maximum Ratings cause permanent damage device. Exposure Absolute Maximum Rating condition extended periods affect device reliability lifetime. Note LT1934E LT1934E-1 guaranteed meet performance specifications from 85°C. Specifications over -40°C 85°C
operating temperature range assured design, characterization correlation with statistical process controls. LT1934I LT1934I-1 specifications guaranteed over -40°C 125°C temperature range. Note This minimum voltage across boost capacitor needed guarantee full saturation internal power switch.
1934fd
LT1934/LT1934-1 TYPICAL PERFORMANCE CHARACTERISTICS
LT1934 Efficiency, VOUT
LT1934 VOUT 25°C
LT1934 Efficiency, VOUT 3.3V
LT1934 VOUT 3.3V 25°C
LT1934-1 Efficiency, VOUT
LT1934-1 VOUT 150H 25°C
EFFICIENCY
EFFICIENCY
EFFICIENCY
LOAD CURRENT (mA)
1934
LOAD CURRENT (mA)
1934
1934
LOAD CURRENT (mA)
LT1934-1 Efficiency, VOUT 3.3V
LT1934-1 VOUT 3.3V 100H 25°C
Current Limit Temperature
LT1934 SWITCH CURRENT LIMIT (mA) TIME
Time Temperature
EFFICIENCY
LT1934-1
1934
LOAD CURRENT (mA)
TEMPERATURE (°C)
TEMPERATURE (°C)
1934
1934
Frequency Foldback
1.27
Temperature
SHDN Bias Current SHDN Voltage
25°C
SHDN CURRENT
1.26 FEEDBACK VOLTAGE
1934
FEEDBACK VOLTAGE
SWITCH TIME
1.25
1.24
1.23
1.22
TEMPERATURE (°C) SHDN VOLTAGE
1934
1934
1934fd
LT1934/LT1934-1 TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Current Temperature
Undervoltage Lockout Temperature
Minimum Input Voltage VOUT 3.3V
LT1934 VOUT 3.3V 25°C BOOST DIODE TIED OUTPUT INPUT VOLTAGE START
QUIESCENT CURRENT
UVLO
TEMPERATURE (°C)
TEMPERATURE (°C)
LOAD CURRENT (mA)
1934
1934
1934
Minimum Input Voltage VOUT
LT1934 VOUT 25°C BOOST DIODE TIED OUTPUT INPUT VOLTAGE START
LOAD CURRENT (mA)
1934
FUNCTIONS
(TSOT-23/DFN)
BOOST (Pin 1/Pin BOOST used provide drive voltage, higher than input voltage, internal bipolar power switch. (Pin 2/Pin local ground plane below LT1934 circuit components. Return feedback divider this pin. (Pin 3/Pin LT1934 regulates feedback 1.25V. Connect feedback resistor divider this pin. output voltage according VOUT 1.25V R1/R2) (VOUT/1.25 SHDN (Pin 4/Pin SHDN used LT1934
shutdown mode. ground shut down LT1934. Apply 2.3V more normal operation. shutdown feature used, this pin. (Pin 5/Pin supplies current LT1934's internal regulator internal power switch. This must locally bypassed. (Pin 6/Pin output internal power switch. Connect this inductor, catch diode boost capacitor. Exposed (Pin Package): This must soldered ground plane.
1934fd
LT1934/LT1934-1 BLOCK DIAGRAM
BOOST TIME DELAY TIME 1.8s DELAY VOUT
SHDN
VREF 1.25V
ENABLE
FEEDBACK COMPARATOR
1934
1934fd
LT1934/LT1934-1 OPERATION
(Refer Block Diagram)
LT1934 uses Burst Mode control, combining both quiescent current operation high switching frequency, which result high efficiency across wide range load currents small total circuit size. comparator monitors voltage LT1934. this voltage higher than internal 1.25V reference, comparator disables oscillator power switch. this state, only comparator, reference undervoltage lockout circuits active, current into just 12A. load current discharges output capacitor, voltage falls below 1.25V comparator enables oscillator. LT1934 begins switch, delivering current output capacitor. output voltage rises, when overcomes feedback comparator's hysteresis, oscillator disabled LT1934 returns micropower state. oscillator consists one-shots flip-flop. rising edge from off-time one-shot sets flip-flop, which turns internal power switch. switch remains until either on-time one-shot trips current limit reached. sense resistor amplifier monitor current through switch resets
flip-flop when this current reaches 400mA (120mA LT1934-1). After 1.8s delay off-time oneshot, cycle repeats. Generally, LT1934 will reach current limit every cycle-the time fixed time regulated that LT1934 operates correct duty cycle. 1.8s time lengthened when voltage falls below 0.8V; this foldback behavior helps control output current during start-up overload. Figure shows several waveforms LT1934 producing 3.3V from input. When switch voltage 10V. When switch off, inductor current pulls down until clamped near ground external catch diode. switch driver operates from either input from BOOST pin. external capacitor diode used generate voltage BOOST that higher than input supply. This allows driver fully saturate bipolar switch efficient operation. SHDN grounded, internal circuits turned current reduces device leakage current, typically
VOUT 50mV/DIV 10V/DIV
0.5A/DIV
0.5A/DIV
1934 F01a
5s/DIV
Figure Operating Waveforms LT1934 Converting 3.3V 180mA (Front Page Schematic)
1934fd
LT1934/LT1934-1 APPLICATIONS INFORMATION
Which Use: LT1934 LT1934-1? only difference between LT1934 LT1934-1 peak current through internal switch inductor. your maximum load current less than 60mA, LT1934-1. your maximum load higher, LT1934; supply ~300mA. While LT1934-1 can't deliver much output current, other advantages. lower peak switch current allows smaller components (input capacitor, inductor output capacitor). ripple current input LT1934-1 circuit will smaller important consideration input supply current limited high impedance. LT1934-1's current draw during faults (output overload short) startup lower. maximum load current that LT1934 LT1934-1 deliver depends value inductor used. Table lists inductor value, minimum output capacitor maximum load 3.3V circuits. Increasing value capacitor will lower output voltage ripple. Component selection covered more detail following sections. Minimum Input Voltage minimum input voltage required generate particular output voltage determined either LT1934's undervoltage lockout maximum duty cycle.
Table
PART LT1934 VOUT 3.3V 100H 150H 150H 100H 220H 150H 100H MINIMUM COUT 100H 4.7H 4.7H MAXIMUM LOAD 300mA 250mA 200mA 300mA 250mA 200mA 60mA 45mA 20mA 60mA 45mA 20mA
duty cycle fraction time that internal switch determined input output voltages: (VOUT VD)/(VIN where forward voltage drop catch diode (~0.4V) voltage drop internal switch (~0.3V maximum load LT1934, ~0.1V LT1934-1). This leads minimum input voltage VIN(MIN) (VOUT VD)/DCMAX with DCMAX 0.85. Inductor Selection good first choice inductor value (VOUT 1.8s/ILIM where ILIM switch current limit (400mA LT1934 120mA LT1934-1). This choice provides worst-case maximum load current 250mA (60mA LT1934-1). inductor's current rating must greater than load current saturation current should greater than ILIM keep efficiency high, series resistance (DCR) should less than LT1934-1). Table lists several vendors types that suitable. This simple rule provide optimum value your application. load current less, then relax value inductor operate with higher ripple current. This allows physically smaller inductor, with lower resulting higher efficiency. following provides more details guide inductor selection. First, value must chosen that LT1934 supply maximum load current drawn from output. Second, inductor must rated appropriately that LT1934 will function reliably inductor itself will overly stressed. Detailed Inductor Selection Maximum Load Current square wave that LT1934 produces switch results triangle wave current inductor. LT1934 limits peak inductor current ILIM Because
1934fd
LT1934-1
3.3V
LT1934/LT1934-1 APPLICATIONS INFORMATION
Table Inductor Vendors
VENDOR Murata Sumida PHONE (404) 426-1300 (847) 956-0666 www.murata.com www.sumida.com PART SERIES LQH3C CR43 CDRH4D28 CDRH5D28 DO1607C DO1608C DT1608C WE-PD1, COMMENTS Small, Cost, Height
Coilcraft
(847) 639-6400
www.coilcraft.com
Electronics
(866) 362-6673
www.we-online.com
average inductor current equals load current, maximum load current IOUT(MAX) where peak inductor current peak-to-peak ripple current inductor. ripple current determined time, tOFF 1.8s, inductor value: (VOUT tOFF nominally equal ILIM However, there slight delay control circuitry that results higher peak current more accurate value ILIM 150ns (VIN VOUT)/L These expressions combined give maximum load current that LT1934 will deliver: IOUT(MAX) 350mA 150ns (VIN VOUT)/L 1.8s (VOUT VD)/2L (LT1934) IOUT(MAX) 90mA 150ns (VIN VOUT)/L 1.8s (VOUT VD)/2L (LT1934-1) minimum current limit used here conservative. third term generally larger than second term, that increasing inductor value results higher output current. This equation used evaluate chosen inductor used choose given maximum load current. simple, single equation rule given above choosing found setting ILIM /2.5. This results IOUT(MAX) ~0.8ILIM (ignoring delay term). Note that this analysis assumes that inductor current continuous, which true ripple current less than peak current IPK.
inductor must carry peak current without saturating excessively. When inductor carries much current, core material longer generate additional magnetic flux saturates) inductance drops, sometimes very rapidly with increasing current. This condition allows inductor current increase very high rate, leading high ripple current decreased overload protection. Inductor vendors provide current ratings power inductors. These based either saturation current current that inductor carry without dissipating much power. some cases clear which these determine current rating. Some data sheets more thorough show current ratings, saturation dissipation. LT1934 applications, current rating should higher than load current, while saturation current should higher than peak inductor current calculated above. Input Capacitor Step-down regulators draw current from input supply pulses with very fast rise fall times. input capacitor required reduce resulting voltage ripple LT1934 force this switching current into tight local loop, minimizing EMI. input capacitor must have impedance switching frequency this effectively. 2.2F ceramic capacitor LT1934-1) satisfies these requirements. input source impedance high, larger value capacitor required keep input ripple low. this case, electrolytic more parallel with ceramic good combination. aware that input
1934fd
LT1934/LT1934-1 APPLICATIONS INFORMATION
capacitor subject large surge currents LT1934 circuit connected impedance supply, that some electrolytic capacitors particular tantalum) must specified such use. Output Capacitor Output Ripple output capacitor filters inductor's ripple current stores energy satisfy load current when LT1934 quiescent. order keep output voltage ripple low, impedance capacitor must LT1934's switching frequency. capacitor's equivalent series resistance (ESR) determines this impedance. Choose with intended switching regulators. contribution ripple voltage approximately ILIM ESR. should less than ~150m LT1934 less than ~500m LT1934-1. value output capacitor must large enough accept energy stored inductor without large change output voltage. Setting this voltage step equal output voltage, output capacitor must COUT (ILIM /VOUT)2 example, LT1934 producing 3.3V with requires 33F. This value relaxed small circuit size more important than output ripple. Sanyo's POSCAP series B-case C-case sizes provides very good performance small package LT1934. Similar performance traditional tantalum capacitors requires larger package D-case).
Table Capacitor Vendors
VENDOR Panasonic PHONE (714) 373-7366 www.panasonic.com PART SERIES Ceramic, Polymer, Tantalum Ceramic, Tantalum Ceramic, Polymer, Tantalum Ceramic, Ceramic, Tantalum Series COMMENTS Series
LT1934-1, with lower switch current, B-case tantalum capacitor. With high quality capacitor filtering ripple current from inductor, output voltage ripple determined hysteresis delay LT1934's feedback comparator. This ripple reduced further adding small (typically 10pF) phase lead capacitor between output feedback pin. Ceramic Capacitors Ceramic capacitors small, robust have very ESR. However, ceramic capacitors cause problems when used with LT1934. ceramic capacitors suitable. types stable over temperature applied voltage give dependable service. Other types (Y5V Z5U) have very large temperature voltage coefficients capacitance. application circuit they have only small fraction their nominal capacitance voltage ripple much larger than expected. Ceramic capacitors piezoelectric. LT1934's switching frequency depends load current, light loads LT1934 excite ceramic capacitor audio frequencies, generating audible noise. this unacceptable, high performance electrolytic capacitor output. input capacitor parallel combination 2.2F ceramic capacitor cost electrolytic capacitor. level noise produced LT1934-1
Kemet Sanyo
(864) 963-6300 (408) 749-9714
www.kemet.com www.sanyovideo.com
T494, T495 POSCAP
Murata Taiyo Yuden
(404) 436-1300
www.murata.com www.avxcorp.com
(864) 963-6300
www.taiyo-yuden.com Ceramic
1934fd
LT1934/LT1934-1 APPLICATIONS INFORMATION
when used with ceramic capacitors will lower acceptable. final precaution regarding ceramic capacitors concerns maximum input voltage rating LT1934. ceramic input capacitor combined with trace cable inductance forms high quality (under damped) tank circuit. LT1934 circuit plugged into live supply, input voltage ring twice nominal value, possibly exceeding LT1934's rating. This situation easily avoided; Plugging Safely section. Catch Diode 0.5A Schottky diode recommended catch diode, diode must have reverse voltage rating equal greater than maximum input voltage. Semiconductor MBR0540 good choice; rated 0.5A forward current maximum reverse voltage 40V. Schottky diodes with lower reverse voltage ratings usually have lower forward drop result higher efficiency with moderate high load currents. However, these diodes also have higher leakage currents. This leakage current mimics load current output raise quiescent current LT1934 circuit, especially elevated temperatures. BOOST Considerations Capacitor diode used generate boost voltage that higher than input voltage. most cases 0.1F capacitor fast switching diode (such 1N4148 1N914) will work well. Figure shows ways arrange boost circuit. BOOST must more than 2.5V above best efficiency. outputs 3.3V above, standard circuit (Figure best. outputs between 2.8V 0.22F capacitor small Schottky diode (such BAT-54). lower output voltages boost diode tied input (Figure 2b). circuit Figure more efficient because BOOST current comes from lower voltage source. must also sure that maximum voltage rating BOOST exceeded. minimum operating voltage LT1934 application limited undervoltage lockout (~3V)
1934
BOOST LT1934 VBOOST VOUT VBOOST VOUT
VOUT
(2a)
BOOST LT1934
VOUT
VBOOST VBOOST 2VIN
(2b) Figure Circuits Generating Boost Voltage
maximum duty cycle outlined above. proper start-up, minimum input voltage also limited boost circuit. input voltage ramped slowly, LT1934 turned with SHDN when output already regulation, then boost capacitor fully charged. Because boost capacitor charged with energy stored inductor, circuit will rely some minimum load current boost circuit running properly. This minimum load will depend input output voltages, arrangement boost circuit. minimum load generally goes zero once circuit started. Figure shows plot minimum load start function input voltage. many cases discharged output capacitor will present load switcher which will allow start. plots show worst-case situation where ramping very slowly. Schottky diode (such BAT-54) lowest start-up voltage. light loads, inductor current becomes discontinuous effective duty cycle very high. This reduces minimum input voltage approximately 300mV above VOUT. higher load currents, inductor current continuous duty cycle limited
1934fd
LT1934/LT1934-1 APPLICATIONS INFORMATION
Minimum Input Voltage VOUT 3.3V
LT1934 VOUT 3.3V 25°C BOOST DIODE TIED OUTPUT
START
VIN), then LT1934's internal circuitry will pull quiescent current through pin. This fine your system tolerate this state. ground SHDN pin, current will drop essentially zero. However, grounded while output held high, then parasitic diodes inside LT1934 pull large currents from output through pin. Figure shows circuit that will only when input voltage present that protects against shorted reversed input.
BOOST LT1934 100k SHDN BACKUP VOUT
INPUT VOLTAGE
LOAD CURRENT (mA)
1934
Minimum Input Voltage VOUT
LT1934 VOUT 25°C BOOST DIODE TIED OUTPUT
INPUT VOLTAGE
START
MBR0530
1934
Figure Diode Prevents Shorted Input from Discharging Backup Battery Tied Output; Also Protects Circuit from Reversed Input. LT1934 Runs Only When Input Present
Layout
LOAD CURRENT (mA)
1934
Figure Minimum Input Voltage Depends Output Voltage, Load Current Boost Circuit
maximum duty cycle LT1934, requiring higher input voltage maintain regulation. Shorted Input Protection inductor chosen that won't saturate excessively, LT1934 buck regulator will tolerate shorted output. There another situation consider systems where output will held high when input LT1934 absent. This occur battery charging applications battery backup systems where battery some other supply diode OR-ed with LT1934's output. allowed float SHDN held high (either logic signal because tied
proper operation minimum EMI, care must taken during printed circuit board layout. Figure shows high current paths buck regulator circuit. Note that large, switched currents flow power switch, catch diode (D1) input capacitor (C2). loop formed these components should small possible. Furthermore, system ground should tied regulator ground only place; this prevents switched current from injecting noise into system ground. These components, along with inductor output capacitor, should placed same side circuit board, their connections should made that layer. Place local, unbroken ground plane below these components, this ground plane system ground location, ideally ground terminal output capacitor Additionally, BOOST nodes should kept small possible. Finally, keep node small possible that ground
1934fd
LT1934/LT1934-1 APPLICATIONS INFORMATION
(5a)
(5b)
1934
(5c) Figure Subtracting Current When Switch from Current When Switch Reveals Path High Frequency Switching Current (c). Keep This Loop Small. Voltage BOOST Nodes Will Also Switched; Keep These Nodes Small Possible. Finally, Make Sure Circuit Shielded with Local Ground Plane
SHUTDOWN VOUT SYSTEM GROUND
VIAS LOCAL GROUND PLANE OUTLINE LOCAL GROUND PLANE
1934
Figure Good Layout Ensures Proper, Operation
ground traces will shield from BOOST nodes. Figure shows component placement with trace, ground plane locations. Include vias near LT1934 help remove heat from LT1934 ground plane. Plugging Safely small size, robustness impedance ceramic capacitors make them attractive option input bypass capacitor LT1934 LT1934-1 circuits. However, these capacitors cause problems LT1934
plugged into live supply (see Linear Technology Application Note complete discussion). loss ceramic capacitor combined with stray inductance series with power source forms under damped tank circuit, voltage LT1934 ring twice nominal input voltage, possibly exceeding LT1934's rating damaging part. input supply poorly controlled user will plugging LT1934 into energized supply, input network should designed prevent this overshoot.
1934fd
LT1934/LT1934-1 APPLICATIONS INFORMATION
Figure shows waveforms that result when LT1934 circuit connected supply through feet 24-gauge twisted pair. first plot response with 2.2F ceramic capacitor input. input voltage rings high input current peaks 20A. method damping tank circuit another capacitor with series resistor circuit. Figure
CLOSING SWITCH SIMULATES PLUG LT1934
aluminum electrolytic capacitor been added. This capacitor's high equivalent series resistance damps circuit eliminates voltage overshoot. extra capacitor improves frequency ripple filtering slightly improve efficiency circuit, though likely largest component circuit. alternative solution shown Figure resistor added
2.2F
10V/DIV
IMPEDANCE ENERGIZED SUPPLY
STRAY INDUCTANCE FEET METERS) TWISTED PAIR
10A/DIV 10s/DIV
(7a)
LT1934
AI.EI.
2.2F
(7b)
LT1934 0.1F 2.2F
(7c)
LT1934-1
(7d)
LT1934-1 0.1F
(7e)
Figure Well Chosen Input Network Prevents Input Voltage Overshoot Ensures Reliable Operation When LT1934 Connected Live Supply
1934
1934fd
LT1934/LT1934-1 APPLICATIONS INFORMATION
series with input eliminate voltage overshoot also reduces peak input current). 0.1F capacitor improves high frequency filtering. This solution smaller less expensive than electrolytic capacitor. high input voltages impact efficiency minor, reducing efficiency less than half percent output full load operating from 24V. Voltage overshoot gets worse with reduced input capacitance. Figure shows plug response with ceramic input capacitor, with input ringing above 40V. LT1934-1 tolerate larger input resistance, such shown Figure where resistor damps voltage transient greatly reduces input current glitch supply. High Temperature Considerations temperature LT1934 must lower than maximum rating 125°C. This generally concern unless ambient temperature above 85°C. higher temperatures, care should taken layout circuit ensure good heat sinking LT1934. maximum load current should derated ambient temperature approaches 125°C. temperature calculated multiplying LT1934 power dissipation thermal resistance from junction ambient. Power dissipation within LT1934 estimated calculating total power loss from efficiency measurement subtracting catch diode loss. resulting temperature rise full load nearly independent input voltage. Thermal resistance depends layout circuit board, value 150°C/W typical TSOT-23 75°C/W DFN. temperature rise LT1934 (TSOT-23) producing 250mA approximately 25°C, allowing deliver full load 100°C ambient. Above this temperature load current should reduced. 3.3V 250mA temperature rise 15°C. temperature rise will roughly one-half these values. Finally, aware that high ambient temperatures external Schottky diode, likely have significant leakage current, increasing quiescent current LT1934 converter. Outputs Greater Than outputs greater than diode (such 1N4148) from prevent from ringing above during discontinuous mode operation. output circuit Typical Applications shows location this diode. Also note that outputs above input voltage range will limited maximum rating BOOST pin. circuit shows overcome this limitation using additional Zener diode.
1934fd
LT1934/LT1934-1 TYPICAL APPLICATIONS
3.3V Step-Down Converter
BOOST 4.5V
0.1F
100H
LT1934-1 SHDN
10pF
VOUT 3.3V 45mA
604k
TAIYO YUDEN JMK316BJ226ML TAIYO YUDEN GMK316BJ105ML ZETEX ZHCS400 SEMI MBR0540 CENTRAL CMDSH-3 COILCRAFT DO1608C-104 WURTH ELECTRONICS WE-PD4 TYPE
1934 TA04
Step-Down Converter
BOOST 6.5V
0.1F
150H
LT1934-1 SHDN
10pF
VOUT 45mA
332k
TAIYO YUDEN JMK316BJ226ML TAIYO YUDEN GMK316BJ105ML ZETEX ZHCS400 SEMI MBR0540 CENTRAL CMPD914 COILCRAFT DO1608C-154 WURTH ELECTRONICS WE-PD4 TYPE
1934 TA05
1934fd
LT1934/LT1934-1 TYPICAL APPLICATIONS
1.8V Step-Down Converter
BOOST 3.6V 2.2F LT1934 SHDN
0.1F
147k
VOUT 1.8V 250mA
100F
332k
SANYO 2R5TPB100M TAIYO YUDEN EMK316BJ225ML ZETEX ZHCS400 SEMI MBR0540 CENTRAL CMPD914 SUMIDA CR43-330
1934 TA06
Loop Powered 3.3V Supply with Additional Isolated Output
ISOLATED
BOOST <3.6mA 390k
10pF
LT1934-1 SHDN
SEMICONDUCTOR MBR0540 BAT54 CENTRAL CMPZ5240B COILTRONICS CTX50-1 ZENER DIODE PROVIDES UNDERVOLTAGE LOCKOUT, REDUCING INPUT CURRENT REQUIRED START-UP
VOUT
715k
1934 TA08
1934fd
LT1934/LT1934-1 TYPICAL APPLICATIONS
Standalone 350mA Li-Ion Battery Charger
0.1F LT1934 SHDN 332k
CHRG ACPR GATE LTC4052 SENSE CTIMER 0.1F (619) 661-6835 (408) 573-4150 (602) 244-6600 (516) 435-1110 (847) 956-0667 CHARGE STATUS PRESENT TIMER
0.047F 0.022F
BOOST
350mA 1-CELL 4.2V Li-Ion BATTERY
1934 TA07a
SANYO 6TPB47M TAIYO YUDEN GMK316BJ105ML SEMICONDUCTOR MBR0540 CENTRAL CMDSH-3 SUMIDA CR43-470
CHARGE CURRENT (mA)
BATTERY VOLTAGE
1934 TA07b
Step-Down Converter
0.1F
BOOST 2.2F LT1934 SHDN
100H
VOUT 170mA 866k
100k
KEMET T495D226K020AS TAIYO YUDEN GMK325BJ225MN SEMI MBR0540 CENTRAL CMPD914 CENTRAL CMPZ5234B 6.2V ZENER SLF6028T-101MR42
1934 TA09
1934fd
LT1934/LT1934-1 PACKAGE DESCRIPTION
Package 6-Lead Plastic TSOT-23
(Reference 05-08-1636)
0.62 0.95 2.90 (NOTE
1.22
3.85 2.62
2.80
1.50 1.75 (NOTE
RECOMMENDED SOLDER LAYOUT CALCULATOR
0.95
0.30 0.45 PLCS (NOTE
0.80 0.90 0.20 1.00 DATUM 0.01 0.10
0.30 0.50 0.09 0.20 (NOTE NOTE: DIMENSIONS MILLIMETERS DRAWING SCALE DIMENSIONS INCLUSIVE PLATING DIMENSIONS EXCLUSIVE MOLD FLASH METAL BURR MOLD FLASH SHALL EXCEED 0.254mm JEDEC PACKAGE REFERENCE MO-193
1.90
TSOT-23 0302
Package 6-Lead Plastic (2mm 3mm)
(Reference 05-08-1715)
2.00 ±0.10 SIDES) 0.70 ±0.05 0.115 0.05 0.40 0.10
3.55 ±0.05
1.65 ±0.05 SIDES) PACKAGE OUTLINE MARK (SEE NOTE
3.00 ±0.10 SIDES)
1.65 0.10 SIDES) NOTCH R0.20 0.25 CHAMFER
(DCB6) 0405
2.15 ±0.05
0.25 0.05 0.50 1.35 ±0.05 SIDES) RECOMMENDED SOLDER PITCH DIMENSIONS
0.200
0.75 ±0.05 1.35 ±0.10 SIDES) 0.00 0.05
0.25 0.05 0.50
BOTTOM VIEW-EXPOSED
NOTE: DRAWING MADE JEDEC PACKAGE OUTLINE M0-229 VARIATION (TBD) DRAWING SCALE DIMENSIONS MILLIMETERS DIMENSIONS EXPOSED BOTTOM PACKAGE INCLUDE MOLD FLASH. MOLD FLASH, PRESENT, SHALL EXCEED 0.15mm SIDE EXPOSED SHALL SOLDER PLATED SHADED AREA ONLY REFERENCE LOCATION BOTTOM PACKAGE
1934fd
LT1934/LT1934-1 TYPICAL APPLICATION
Step-Down Converter
BOOST 6.5V 2.2F LT1934 SHDN
0.1F
10pF
VOUT 250mA
332k
SANYO 6TPB68M TAIYO YUDEN GMK325BJ225MN ZETEX ZHCS400 SEMI MBR0540 CENTRAL CMPD914 SUMIDA CDRH5D28-680
1934 TA03
RELATED PARTS
PART NUMBER LT1616 LT1676 LT1765 LT1766 LT1767 LT1776 LTC®1877 LTC1879 LT1956 DESCRIPTION 25V, 500mA (IOUT), 1.4MHz, High Efficiency Step-Down DC/DC Converter 60V, 440mA (IOUT), 100kHz, High Efficiency Step-Down DC/DC Converter 25V, 2.75A (IOUT), 1.25MHz, High Efficiency Step-Down DC/DC Converter 60V, 1.2A (IOUT), 200kHz, High Efficiency Step-Down DC/DC Converter 25V, 1.2A (IOUT), 1.25MHz, High Efficiency Step-Down DC/DC Converter 40V, 550mA (IOUT), 200kHz, High Efficiency Step-Down DC/DC Converter 600mA (IOUT), 550kHz, Synchronous Step-Down DC/DC Converter 1.2A (IOUT), 550kHz, Synchronous Step-Down DC/DC Converter 60V, 1.2A (IOUT), 500kHz, High Efficiency Step-Down DC/DC Converter COMMENTS 3.6V 25V, VOUT 1.25V, 1.9mA <1A, ThinSOT Package 7.4V 60V, VOUT 1.24V, 3.2mA 2.5A, Package 25V, VOUT 1.2V, 15A, TSSOP16E Packages 5.5V 60V, VOUT 1.2V, 2.5mA 25A, TSSOP16/E Package 25V; VOUT 1.2V, 1mA, MS8/E Packages 7.4V 40V; VOUT 1.24V, 3.2mA, 30A, Packages 2.7V 10V; VOUT 0.8V, 10A, <1A, Package 2.7V 10V; VOUT 0.8V, 15A, <1A, TSSOP16 Package 5.5V 60V, VOUT 1.2V, 2.5mA, 25A, TSSOP16/E Package 2.7V VOUT 0.8V, 20A, <1A, ThinSOT Package 2.5V 5.5V, VOUT 0.6V, 20A, <1A, ThinSOT Package 2.5V 5.5V, VOUT 0.8V, 60A, <1A, Package 2.5V 5.5V, VOUT 0.8V, 60A, <1A, TSSOP16E Package 5.5V 60V, VOUT 1.2V, 2.5mA, 30A, TSSOP16E Package
1934fd 0708 PRINTED
LTC3405/LTC3405A 300mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter LTC3406/LTC3406B 600mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter LTC3411 LTC3412 LTC3430 1.25A (IOUT), 4MHz, Synchronous Step-Down DC/DC Converter 2.5A (IOUT), 4MHz, Synchronous Step-Down DC/DC Converter 60V, 2.75A (IOUT), 200kHz, High Efficiency Step-Down DC/DC Converter
Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
1630 McCarthy Blvd., Milpitas, 95035-7417
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2002
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