DESCRIPTIO 1.5A Switch Small MSOP Package Constant 1.25MHz Switch

The Datasheet Archive - 100 Million Datasheets from 7500 Manufacturers.

DESCRIPTIO 1.5A Switch Small MSOP Package Constant 1.25MHz Switch

Datasheet Thumbnail

Top Searches for this datasheet

LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5 Monolithic 1.5A, 1.25MHz Step-Down Switching Regulators
DESCRIPTIO
1.5A Switch Small MSOP Package Constant 1.25MHz Switching Frequency High Power Exposed (MS8E) Package Wide Operating Voltage Range: High Efficiency 0.22 Switch 1.2V Feedback Reference Voltage Fixed Output Voltages 1.8V, 2.5V, 3.3V, Overall Output Tolerance Uses Profile Surface Mount Components Shutdown Current: Synchronizable 2MHz Current Mode Loop Control Constant Maximum Switch Current Rating Duty Cycles*
LT®1767 1.25MHz monolithic buck switching regulator. high efficiency 1.5A, 0.22 switch included together with control circuitry required complete high frequency, current mode switching regulator. Current mode control provides fast transient response excellent loop stability. design techniques achieve high efficiency high switching frequencies over wide operating range. dropout internal regulator maintains consistent performance over wide range inputs from systems LiIon batteries. operating supply current improves efficiency, especially lower output currents. Shutdown reduces quiescent current 6µA. Maximum switch current remains constant duty cycles. Synchronization allows external logic level signal increase internal oscillator from 1.4MHz 2MHz. LT1767 available 8-pin MSOP fused leadframe package thermal resistance exposed package. Full cycle-by-cycle short-circuit protection thermal shutdown provided. High frequency operation allows reduction input output filtering components permits chip inductors.
registered trademarks Linear Technology Corporation. *Patent Pending
APPLICATIO
Modems Portable Computers Wall Adapters Battery-Powered Systems Distributed Power
TYPICAL APPLICATIO
3.3V Step-Down Converter
CMDSH-3 0.1µF BOOST OPEN HIGH LT1767-3.3 SHDN SYNC 1.5nF 4.7k *MAXIMUM OUTPUT CURRENT SUBJECT THERMAL DERATING.
1767 TA01
EFFICIENCY
2.2µF CERAMIC
OUTPUT 3.3V 1.2A*
UPS120
10µF CERAMIC
Efficiency Load Current
VOUT VOUT 3.3V LOAD CURRENT
1767 TA01a
sn1767 1767fas
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5
ABSOLUTE MAXIMUM RATINGS
Input Voltage BOOST Above BOOST Voltage SHDN Voltage Current
PACKAGE/ORDER INFORMATION
ORDER PART NUMBER
VIEW BOOST SYNC SHDN
PACKAGE 8-LEAD PLASTIC MSOP TJMAX 125°C, 110°C/W GROUND CONNECTED LARGE COPPER AREA
LT1767EMS8 LT1767EMS8-1.8 LT1767EMS8-2.5 LT1767EMS8-3.3 LT1767EMS8-5 PART MARKING LTLS LTWG LTWD LTWE LTWF
Consult Marketing parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. 15V, 0.8V, Boost SHDN, SYNC switch open unless otherwise noted.
PARAMETER Maximum Switch Current Limit Oscillator Frequency Switch Voltage Drop Undervoltage Lockout Supply Current Shutdown Supply Current Feedback Voltage CONDITION 125°C 3.3V
-1.5A, 125°C -1.3A,
(Note VNOM VSHDN 25V,
25V, 0.4V 0.9V (Note
Input Current
LT1767 (Adj)
(Note
SYNC Current Operating Junction Temperature Range (Note LT1767E 40°C 125°C Storage Temperature Range 65°C 150°C Lead Temperature (Soldering, sec). 300°C
ORDER PART NUMBER
VIEW BOOST SYNC SHDN
MS8E PACKAGE 8-LEAD PLASTIC MSOP TJMAX 125°C, 40°C/W EXPOSED CONNECTED LARGE COPPER AREA
LT1767EMS8E LT1767EMS8E-1.8 LT1767EMS8E-2.5 LT1767EMS8E-3.3 LT1767EMS8E-5 MS8E PART MARKING LTZG LTZH LTZJ LTZK LTZL
1.25
2.73 1.218 1.224 1.836 2.55 3.366
UNITS
2.47
LT1767 (Adj)
1.182 1.176 1.764 2.45 3.234
0.25
LT1767-1.8 LT1767-2.5 LT1767-3.3 LT1767-5
sn1767 1767fas
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5
ELECTRICAL CHARACTERISTICS
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. 15V, 0.8V, Boost SHDN, SYNC switch open unless otherwise noted.
PARAMETER Input Resistance CONDITION LT1767-1.8 LT1767-2.5 LT1767-3.3 LT1767-5 0.4V 0.9V ±10µA VNOM VNOM Duty Cycle 1.2V, 400mA
10.5 14.7
27.5 0.35
1300
UNITS µMho
Error Voltage Gain Error Transconductance Source Current Sink Current Switch Current Transconductance Minimum Switching Threshold 1.5A Threshold Maximum Switch Duty Cycle Minimum Boost Voltage Above Switch Boost Current SHDN Threshold Voltage SHDN Input Current (Shutting Down) SHDN Threshold Current Hysteresis SYNC Threshold Voltage SYNC Input Frequency SYNC Resistance
1.40
-1.5A, 125°C -1.3A, 0.5A (Note -1.5A, 125°C -1.3A, (Note SHDN 60mV Above Threshold SHDN 100mV Below Threshold
1.27
1.33
ISYNC
Note Absolute Maximum Ratings those values beyond which life device impaired. Note LT1767E guaranteed meet performance specifications from 125°C. Specifications over 40°C 125°C operating junction temperature range assured design, characterization correlation with statistical process controls.
Note Minimum input voltage defined voltage where internal regulator enters lockout. Actual minimum input voltage maintain regulated output will depend output voltage load current. Applications Information. Note Current flows into BOOST only during period switch cycle.
TYPICAL PERFORMANCE CHARACTERISTICS
Temperature (Adj)
1.22 125°C
SWITCH VOLTAGE (mV)
1.21
FREQUENCY (MHz)
VOLTAGE
1.20
1.19
1.18
TEMPERATURE (°C)
Switch Voltage Drop
1.50 1.45
25°C
Oscillator Frequency
1.40 1.35 1.30 1.25 1.20 1.15 1.10 TEMPERATURE (°C)
-40°C
1767
SWITCH CURRENT
1767
1767
sn1767 1767fas
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5 TYPICAL PERFOR CHARACTERISTICS
SHDN Threshold Temperature
1.40
1.38
SHDN THRESHOLD
CURRENT (µA)
SHDN INPUT (µA)
1.36
1.34
1.32
1.30
TEMPERATURE (°C)
Minimum Input Voltage 2.5V
INPUT VOLTAGE CURRENT (µA)
CURRENT (µA)
0.001
0.01 LOAD CURRENT
Current Limit Foldback
SWITCH PEAK CURRENT
OUTPUT CURRENT
SWITCH CURRENT
OUTPUT CURRENT
CURRENT
FEEDBACK VOLTAGE
1767
SHDN Supply Current
SHDN
1767
SHDN Current Temperature
SHUTTING DOWN
STARTING
TEMPERATURE (°C)
1767
SHDN Supply Current
1200 1000
Input Supply Current
MINIMUM INPUT VOLTAGE
1767
SHUTDOWN VOLTAGE
INPUT VOLTAGE
1767
1767
Maximum Load Current, VOUT
Maximum Load Current, VOUT 2.5V
4.7µH
4.7µH
INPUT CURRENT (µA)
2.2µH 1.5µH
2.2µH
1.5µH
1767
INPUT VOLTAGE
1767
INPUT VOLTAGE
1767
sn1767 1767fas
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5
FUNCTIONS
feedback used output voltage using external voltage divider that generates 1.2V with desired output voltage. fixed voltage 1.8V, 2.5V, 3.3V versions have divider network included internally connected directly output. required, current limit reduced during start short-circuit when below 0.5V (see Current Limit Foldback graph Typical Performance Characteristics section). impedance less than (adjustable part only) needed this feature operate. BOOST: BOOST used provide drive voltage, higher than input voltage, internal bipolar power switch. Without this added voltage, typical switch voltage loss would about 1.5V. additional boost voltage allows switch saturate voltage loss approximates that 0.22 structure. VIN: This collector on-chip power switch. This powers internal circuitry internal regulator. switch off, high dI/dt edges occur this pin. Keep external bypass capacitor catch diode close this pin. trace inductance this path will create voltage spike switch off, adding voltage across internal NPN. GND: acts reference regulated output, load regulation will suffer "ground" load same voltage This condition will occur when load current other currents flow through metal paths between load ground point. Keep ground path short between load ground plane when possible. Keep path between input bypass short. package directly attached internal tab. This should attached large copper area improve thermal resistance. exposed MS8E package also connected GND. This should soldered large copper area improve thermal resistance. VSW: switch emitter on-chip power switch. This driven input voltage during switch time. Inductor current drives switch negative during switch time. Negative voltage must clamped with external catch diode with <0.8V. SYNC: sync used synchronize internal oscillator external signal. directly logic compatible driven with signal between duty cycle. synchronizing range equal initial operating frequency, 2MHz. Synchronization section Applications Information details. When use, this should grounded. SHDN: shutdown used turn regulator reduce input drain current microamperes. 1.33V threshold function accurate undervoltage lockout (UVLO), preventing regulator from operating until input voltage reached predetermined level. Float pull high regulator operating mode. output error amplifier input peak switch current comparator. normally used frequency compensation, double duty current clamp control loop override. This sits about 0.35V very light loads 0.9V maximum load. driven ground shut output.
sn1767 1767fas
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5
BLOCK DIAGRAM
LT1767 constant frequency, current mode buck converter. This means that there internal clock feedback loops that control duty cycle power switch. addition normal error amplifier, there current sense amplifier that monitors switch current cycle-by-cycle basis. switch cycle starts with oscillator pulse which sets flip-flop turn switch When switch current reaches level inverting input comparator, flip-flop reset switch turns off. Output voltage control obtained using output error amplifier switch current trip point. This technique means that error amplifier commands current delivered output rather than voltage. voltage system will have phase shift resonant frequency inductor
0.01
2.5V BIAS REGULATOR
SYNC
SHUTDOWN COMPARATOR
1.33V
ERROR AMPLIFIER 850µMho
Figure Block Diagram
sn1767 1767fas
SHDN
output capacitor, then abrupt 180° shift will occur. current system will have phase shift much lower frequency, will have additional shift until well beyond resonant frequency. This makes much easier frequency compensate feedback loop also gives much quicker transient response. High switch efficiency attained using BOOST provide voltage switch driver which higher than input voltage, allowing switch saturated. This boosted voltage generated with external capacitor diode. comparator connected shutdown disables internal regulator, reducing supply current.
INTERNAL
CURRENT SENSE AMPLIFIER VOLTAGE GAIN
SLOPE COMP
0.35V
BOOST
1.25MHz OSCILLATOR
CURRENT COMPARATOR
FLIP-FLOP
DRIVER CIRCUITRY
POWER SWITCH
PARASITIC DIODES FORWARD BIAS
1.2V
1767
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5
APPLICATIONS INFORMATION
RESISTOR NETWORK output voltage 1.8V, 2.5V, 3.3V required, respective fixed option part, -1.8, -2.5, -3.3 should used. tied directly output; necessary resistive divider already included part. other voltage outputs, adjustable part should used external resistor divider added. suggested resistor (R2) from ground 10k. This reduces contribution input bias current output voltage less than 0.25%. formula resistor (R1) from VOUT capacitance less important significant effect loop stability. operation required close minimum input required output LT1767, larger value required. This prevent excessive ripple causing dips below minimum operating voltage, resulting erratic operation. tantalum capacitors used, values 22µF 470µF range generally needed minimize meet ripple current surge ratings. Care should taken ensure ripple surge ratings exceeded. Kemet T495 series surge rated. recommends derating capacitor operating voltage high surge applications. OUTPUT CAPACITOR
OUTPUT
VOUT
R2(0.25µA)
ERROR AMPLIFIER
LT1767
1.2V
1767
Figure Feedback Network
INPUT CAPACITOR Step-down regulators draw current from input supply pulses. rise fall times these pulses very fast. input capacitor required reduce voltage ripple this causes input LT1767 force switching current into tight local loop, thereby minimizing EMI. ripple current calculated from:
IRIPPLE(RMS) IOUT VOUT VOUT
VIN2
Higher value, lower cost ceramic capacitors available smaller case sizes. These ideal input bypassing since their high frequency capacitive nature removes most ripple current rating turn-on surge problems. higher switching frequency, energy storage requirement input capacitor reduced values range 4.7µF suitable most applications. similar type ceramics used since absolute value
Unlike input capacitor, ripple current output capacitor normally enough that ripple current rating issue. current waveform triangular, with value given IRIPPLE(RMS) 0.29 VOUT VOUT
(L)(f)(VIN)
LT1767 will operate with both ceramic tantalum output capacitors. Ceramic capacitors generally chosen their small size, very (effective series resistance), good high frequency operation, reducing output ripple voltage. Their removes useful zero loop frequency response, common tantalum capacitors. compensate this, loop compensation pole frequency must typically reduced factor Typical ceramic output capacitors 10µF range. Since absolute value capacitance defines pole frequency output stage, type ceramic, which have good temperature stability, recommended. Tantalum capacitors usually chosen their bulk capacitance properties, useful high transient load applications. rather than capacitive value defines output ripple 1.25MHz. Typical LT1767 applications require tantalum capacitor with less than 22µF 500µF, Table
sn1767 1767fas
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5
APPLICATIONS INFORMATION
Table Surface Mount Solid Tantalum Capacitor Ripple Current Case Size (Max, Ripple Current
TPS, Sprague 593D Case Size TPS, Sprague 593D Case Size (typ) (typ)
Figure shows comparison output ripple ceramic tantalum capacitor 200mA ripple current.
VOUT USING 47µF, TANTALUM CAPACITOR (10mV/DIV)
VOUT USING 2.2µF CERAMIC CAPACITOR (10mV/DIV)
(5V/DIV)
0.2µs/DIV
Figure Output Ripple Voltage Waveform
INDUCTOR CHOICE MAXIMUM OUTPUT CURRENT Maximum output current buck converter equal maximum switch rating (IP) minus half peak peak inductor current. past designs, maximum switch current been reduced introduction slope compensation. Slope compensation required duty cycles above prevent affect called subharmonic oscillation (see Application Note details). LT1767 circuit technique that maintains constant switch current rating duty cycles. (Patent Pending) most applications, output inductor will 10µH range. Lower values chosen reduce physical size inductor, higher values allow higher output currents reduced peak peak ripple current,
reduces current which discontinuous operation occurs. following formula gives maximum output current continuous mode operation, implying that peak peak ripple term right) less than maximum switch current. Continuous Mode IOUT (MAX)
(VOUT )(VIN VOUT 2(L)( f)(VIN
Discontinuous operation occurs when
IOUT (DIS)
(VOUT 2(L)(f)
VOUT 3.3µH, IOUT (MAX)
1.25
0.23 1.27 Note that worst case (minimum output current available) condition maximum input voltage. same circuit 15V, maximum output current would only 1.1A.
1767
(5)(8
When choosing inductor, consider maximum load current, core copper losses, allowable component height, output voltage ripple, EMI, fault current inductor, saturation, course, cost. following procedure suggested handling these somewhat complicated conflicting requirements. Choose value microhenries from graphs maximum load current. Choosing small inductor with lighter loads result discontinuous mode operation, LT1767 designed work well either mode. Assume that average inductor current equal load current decide whether inductor must withstand continuous fault conditions. maximum load current 0.5A, instance, 0.5A inductor survive continuous overload condition. Also, instantaneous application input release from shutdown, high input voltages, cause
sn1767 1767fas
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5
APPLICATIONS INFORMATION
saturation inductor. these applications, soft-start circuit shown Figure should used. Calculate peak inductor current full load current ensure that inductor will saturate. Peak current significantly higher than output current, especially with smaller inductors lighter loads, don't omit this step. Powdered iron cores forgiving because they saturate softly, whereas ferrite cores saturate abruptly. Other core materials fall somewhere between. IPEAK IOUT VOUT VOUT After making initial choice, consider secondary things like output voltage ripple, second sourcing, etc. experts Linear Technology's applications department feel uncertain about final choice. They have experience with wide range inductor types tell about latest developments profile, surface mounting, etc. CATCH DIODE suggested catch diode (D1) UPS120 Schottky, Motorola equivalent, MBRM120LTI/MBRM130LTI. rated average forward current 20V/30V reverse voltage. Typical forward voltage 0.5V diode conducts current only during switch time. Peak reverse voltage equal regulator input voltage. Average forward current normal operation calculated from:
AVG) IOUT VOUT
Maximum input voltage Switching frequency, 1.25MHz Decide design tolerate "open" core geometry like barrel, which have high magnetic field radiation, whether needs closed core like toroid prevent problems. This tough decision because rods barrels temptingly cheap small there helpful guidelines calculate when magnetic field radiation will problem.
Table
PART NUMBER Coiltronics TP1-2R2 TP2-2R2 TP3-4R7 TP4- Murata LQH1C1R0M04 LQH3C1R0M24 LQH3C2R2M24 LQH4C1R5M04 Sumida CD73- CDRH4D18-2R2 CDRH5D18-6R2 CDRH5D28-100 1.44 1.32 0.080 0.058 0.071 0.048 0.51 0.79 0.28 0.06 0.09 0.188 0.111 0.181 0.146 VALUE (uH) ISAT(Amps) HEIGHT (mm)
BOOST most applications, boost components 0.1µF capacitor CMDSH-3 diode. anode typically connected regulated output voltage generate voltage approximately VOUT above drive output stage. output driver requires least 2.7V headroom throughout period keep switch fully saturated. However, output stage discharges boost capacitor during time. output voltage less than 3.3V, recommended that alternate boost supply used. boost diode connected input, although, care must taken prevent boost voltage from exceeding BOOST absolute maximum rating. additional voltage across switch driver also increases power loss, reducing efficiency. available, independent supply used with local bypass capacitor. 0.1µF boost capacitor recommended most applications. Almost type film ceramic capacitor
sn1767 1767fas
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5
APPLICATIONS INFORMATION
suitable, should ensure fully recharged during time switch. capacitor value derived from worst-case conditions 700ns on-time, 50mA boost current, 0.7V discharge ripple. This value then guard banded secondary factors such capacitor tolerance, temperature effects. boost capacitor value could reduced under less demanding conditions, this will improve circuit operation efficiency. Under input voltage load conditions, higher value capacitor will reduce discharge ripple improve start operation. SHUTDOWN UNDERVOLTAGE LOCKOUT Figure shows undervoltage lockout (UVLO) LT1767. Typically, UVLO used situations where input supply current limited, relatively high source resistance. switching regulator draws constant power from source, source current increases source voltage drops. This looks like negative resistance load source cause source current limit latch under source voltage conditions. UVLO prevents regulator from operating source voltages where these problems might occur.
LT1767 1.33V OUTPUT
SHDN
Figure Undervoltage Lockout
internal comparator will force part into shutdown below minimum 2.6V. This feature used prevent excessive discharge battery-operated systems. adjustable UVLO threshold required, shutdown used. threshold voltage shutdown comparator 1.33V. internal current source defaults open condition operating (see Typical Performance Graphs). Current hysteresis added above SHDN threshold. This used voltage hysteresis UVLO using following:
1.33V)
1.33V
Turn-on threshold Turn-off threshold Example: switching should start until input above 4.75V stop input falls below 3.75V. 4.75V 3.75V 4.75V 3.75V 143k 1.33V 143k
(4.75V 1.33V)
49.4k
Keep connections from resistors SHDN short make sure that interplane surface capacitance switching nodes minimized. high resistor values used, SHDN should bypassed with capacitor prevent coupling problems from switch node. SYNCHRONIZATION
1767
SYNC pin, used synchronize internal oscillator external signal. SYNC input must pass from logic level low, through maximum synchronization threshold with duty cycle between 80%. input driven directly from logic level output. synchronizing range equal initial operating frequency 2MHz. This means that minimum practical sync frequency equal worst-case high self-oscillating frequency (1.5MHz), typical operating frequency 1.25MHz. Caution should used when synchronizing above 1.6MHz because higher sync frequencies amplitude internal slope compensation used
sn1767 1767fas
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5
APPLICATIONS INFORMATION
prevent subharmonic switching reduced. This type subharmonic switching only occurs input voltages less than twice output voltage. Higher inductor values will tend eliminate this problem. Frequency Compensation section discussion entirely different cause subharmonic switching before assuming that cause insufficient slope compensation. Application Note more details theory slope compensation. LAYOUT CONSIDERATIONS with high frequency switchers, when considering layout, care must taken order achieve optimal electrical, thermal noise performance. maximum efficiency, switch rise fall times typically nanosecond range. prevent noise both radiated conducted, high speed switching current path, shown Figure must kept short possible. This implemented suggested layout Figure Shortening this path will also reduce parasitic trace inductance approximately 25nH/inch. switch off, this parasitic inductance produces flyback spike across LT1767 switch. When operating higher currents input voltages, with poor layout, this spike generate voltages across LT1767 that exceed absolute maximum rating. ground plane should always used under switcher circuitry prevent interplane coupling overall noise.
LT1767
HIGH FREQUENCY CIRCULATING PATH
LOAD
Figure High Speed Switching Path
components should kept away possible from switch boost nodes. LT1767 pinout been designed this. ground these components should separated from switch current path. Failure will result poor stability subharmonic like oscillation.
Board layout also significant effect thermal resistance. Soldering exposed large copper area possible placing feedthroughs under ground plane, will reduce temperature increase power capacity LT1767. nonexposed package, connected directly inside package. Similar treatment this will result lower temperatures. THERMAL CALCULATIONS Power dissipation LT1767 chip comes from four sources: switch loss, switch loss, boost circuit current, input quiescent current. following formulas show calculate each these losses. These formulas assume continuous mode operation, they should used calculating efficiency light load currents. Switch loss:
IOUT
Boost current loss VBOOST VOUT:
(VOUT 17ns(IOUT )(VIN)(f)
PBOOST
VOUT IOUT
Quiescent current loss:
0.001
Switch resistance 0.27 when hot) 17ns Equivalent switch current/voltage overlap time Switch frequency Example: with 10V, VOUT IOUT
1767
(0.27)(1) 10-9 (1)(10) 1.25
0.135 0.21 0.34
0.05W PBOOST
0.001 0.01W
sn1767 1767fas
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5
APPLICATIONS INFORMATION
CMDSH-3 0.1µF BOOST OPEN HIGH LT1767-2.5 SHDN SYNC 1.5nF 4.7k
1767 F06a
2.2µF CERAMIC
MINIMIZE LT1767, LOOP
Figure Typical Application Suggested Layout (Topside Only Shown)
Total power dissipation 0.34 0.05 0.01 0.4W. Thermal resistance LT1767 package influenced presence internal backside planes. With full plane under package, thermal resistance exposed package will about 40°C/W. plane will increase resistance about 150°C/W. calculate temperature, appropriate thermal resistance number worst-case ambient temperature: (PTOT)
OUTPUT 2.5V 1.2A
UPS120
10µF CERAMIC
PLACE FEEDTHROUGHS AROUND GROUND UNDER GROUND GOOD THERMAL CONDUCTIVITY SYNC KEEP COMPONENTS AWAY FROM HIGH INPUT COMPONENTS
SHDN
VOUT
CONNECT GROUND PLANE
KELVIN SENSE VOUT
1767
When estimating ambient, remember nearby catch diode inductor will also dissipating power.
PDIODE
)(VIN VOUT )(ILOAD
Forward voltage diode (assume 0.5V
PDIODE
(0.5)(12 5)(1) 0.29W
sn1767 1767fas
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5
APPLICATIONS INFORMATION
Notice that catch diode's forward voltage contributes significant loss overall system efficiency. larger, lower diode improve efficiency several percent. PINDUCTOR (ILOAD) (LDCR) LDCR Inductor resistance (assume 0.1) PINDUCTOR (0.1) 0.1W Typical thermal resistance board 35°C/W. ambient temperature 65°C, (0.4) (0.39) 95°C true temperature required, measurement SYNC resistance used. SYNC resistance across temperature must first calibrated, with device power, oven. same measurement then used operation indicate temperature.
GAIN (dB)
500k LT1767 CURRENT MODE POWER STAGE 2.5mho ERROR AMPLIFIER 850µmho TANTALUM CERAMIC OUTPUT
Figure Model Loop Response
VOUT COUT 100µF, 330pF RC/CF ILOAD 500mA PHASE GAIN
1767
FREQUENCY COMPENSATION Before starting theoretical analysis frequency response, following should remembered worse board layout, more difficult circuit will stabilize. This true almost high frequency analog circuits, read `LAYOUT CONSIDERATIONS' section first. Common layout errors that appear stability problems distant placement input decoupling capacitor and/or catch diode, connecting compensation ground track carrying significant switch current. addition, theoretical analysis considers only first order non-ideal component behavior. these reasons, important that final stability check made with production layout components. LT1767 uses current mode control. This alleviates many phase shift problems associated with inductor. basic regulator loop shown Figure with both tantalum ceramic capacitor equivalent circuits. LT1767 considered blocks, error amplifier power stage. Figure shows overall loop response with 330pF capacitor typical 100µF tantalum output capacitor. response following terms:
Figure Overall Loop Response
Error amplifier: gain 850µ 500k 425. Pole 500k 330p)-1 965Hz. Unity-gain 330p 850µ-1)-1 410kHz. Power stage: gain (assume Pole COUT 100µ 10)-1 159Hz. Unity-gain COUT 100µ 2.5-1)-1 3.98kHz. Tantalum output capacitor: Zero COUT CESR 100µ 0.1)-1 15.9kHz.
1.2V
1767
PHASE (DEG)
FREQUENCY (Hz)
100k
sn1767 1767fas
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5
APPLICATIONS INFORMATION
zero produced tantalum output capacitor very useful maintaining stability. Ceramic output capacitors have zero very ESR, dominated their ESL. They form notch 1MHz 10MHz range. Without this zero, pole must made dominant. typical value 2.2nF will achieve this. better transient response required, zero added loop using resistor (RC) series with compensation capacitor. value increased, transient response will generally improve, effects limit value. First, combination output capacitor large stop loop gain rolling altogether. Second, loop gain rolled sufficiently switching frequency, output ripple will perturb enough cause unstable duty cycle switching similar subharmonic oscillation. This apparent output. Small signal analysis will show this since continuous time system assumed. needed, additional capacitor (CF) added form pole typically fifth switching frequency 100pF). When checking loop stability, circuit should operated over application's full voltage, current temperature range. transient loads should applied output voltage monitored well-damped behavior. Application Note more details. CONVERTER WITH BACKUP OUTPUT REGULATOR systems with primary backup supply, example, battery powered device with wall adapter input, output LT1767 held backup supply with input disconnected. this condition, will source current into pin. SHDN held ground, only shut down current will pulled from second supply. With SHDN floating, LT1767 will consume quiescent operating current 1mA. will also source current other components connected input line. this load greater than 10mA input could shorted ground, series Schottky diode must added, shown Figure With these safeguards, output held voltages absolute maximum rating. BUCK CONVERTER WITH ADJUSTABLE SOFT-START Large capacitive loads high input voltages cause high input currents start-up. Figure shows circuit that limits dv/dt output start-up, controlling capacitor charge rate. buck converter typical configuration with addition output starts rise, turns regulating switch current maintain constant dv/dt output. Output rise time controlled current through defined Q1's VBE. Once output regulation, turns circuit operates normally. transient protection base
RiseTime (R4)(C )(VOUT (VBE
Using values shown Figure
RiseTime
)(15 10-9 )(5)
ramp linear rise times order 100ms possible. Since circuit voltage controlled, ramp rate unaffected load characteristics maximum output current unchanged. Variants this circuit used sequencing multiple regulator outputs. Dual Output SEPIC Converter circuit Figure generates both positive negative outputs with single piece magnetics. inductors shown actually just windings standard Electronics inductor. topology output standard buck converter. topology would simple flyback winding coupled buck converter were present. creates SEPIC (single-ended primary inductance converter) topology which improves regulation reduces ripple current Without voltage swing compared would vary relative loading coupling losses. provides impedance path maintain equal voltage swing L1B, improving regulation. flyback converter, during switch time, converter's energy stored only, since current flows L1B. switch off, energy transferred magnetic coupling into L1B, powering rail. pulls positive
sn1767 1767fas
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5
APPLICATIONS INFORMATION
during switch time, causing current flow, energy build switch off, energy stored both supply rail. This reduces current changes current waveform from square triangular. details this circuit, including maximum output currents, Design Note 100.
CMDSH-3 0.1µF UPS120* REMOVABLE INPUT LT1767-3.3 SHDN SYNC 28.5k 2.2µF 4.7k
1767
ONLY REQUIRED INPUT SINK >10mA
Figure Dual Source Supply with Reverse Leakage
0.1µF
CMDSH-3 0.1µF BOOST LT1767-5 SHDN SYNC 330pF UPS120 2N3904 15nF
1767
2.2µF
100µF
Figure Buck Converter with Adjustable Soft-Start
PACKAGE DESCRIPTION
Package 8-Lead Plastic MSOP
(Reference 05-08-1660)
0.043 (1.10) 0.007 (0.18) 0.021 0.006 (0.53 0.015) SEATING PLANE 0.193 0.006 (4.90 0.15) 0.118 0.004** (3.00 0.102) 0.034 (0.86) 0.118 0.004* (3.00 0.102)
0.009 0.015 (0.22 0.38)
DIMENSION DOES INCLUDE MOLD FLASH, PROTRUSIONS GATE BURRS. MOLD FLASH, PROTRUSIONS GATE BURRS SHALL EXCEED 0.006" (0.152mm) SIDE DIMENSION DOES INCLUDE INTERLEAD FLASH PROTRUSIONS. INTERLEAD FLASH PROTRUSIONS SHALL EXCEED 0.006" (0.152mm) SIDE
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.
BOOST 1.5nF UPS120
3.3V, ALTERNATE SUPPLY
2.2µF
CMDSH-3
BOOST LT1767-5 SHDN SYNC 2.2µF CERAMIC 330pF
L1A*
OUTPUT
OUTPUT
100µF TANT
2.2µF SINGLE CORE WITH WINDINGS ELECTRONICS #511-1013 LOAD ZERO, CERAMIC OPTIONAL PRELOAD USED IMPROVE LOAD REGULATION UPS120
L1B* 100µF TANT
OUTPUT
1767
Figure Dual Output SEPIC Converter
0.0256 (0.65)
0.005 0.002 (0.13 0.05)
MSOP (MS8) 1100
sn1767 1767fas
LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5
PACKAGE DESCRIPTION
MS8E Package 8-Lead Plastic MSOP
(Reference 05-08-1662)
0.889 0.127 (.035 .005) 3.00 0.102 (.118 .004) (NOTE BOTTOM VIEW EXPOSED OPTION 0.52 (.206) 2.06 0.102 (.080 .004) 1.83 0.102 (.072 .004)
2.794 0.102 (.110 .004)
5.23 (.206)
2.083 0.102 3.45 (.082 .004) (.126 .136)
0.42 0.04 (.0165 .0015)
0.65 (.0256)
GAUGE PLANE 0.53 0.015 (.021 .006) DETAIL 0.18 (.077) 1.10 (.043) 0.86 (.034)
RECOMMENDED SOLDER LAYOUT
NOTE: DIMENSIONS MILLIMETER/(INCH) DRAWING SCALE DIMENSION DOES INCLUDE MOLD FLASH, PROTRUSIONS GATE BURRS. MOLD FLASH, PROTRUSIONS GATE BURRS SHALL EXCEED 0.152mm (.006") SIDE DIMENSION DOES INCLUDE INTERLEAD FLASH PROTRUSIONS. INTERLEAD FLASH PROTRUSIONS SHALL EXCEED 0.152mm (.006") SIDE LEAD COPLANARITY (BOTTOM LEADS AFTER FORMING) SHALL 0.102mm (.004")
RELATED PARTS
PART NUMBER LT1370 LT1371 LT1372/LT1377 LT1374 LT1375/LT1376 LT1507 LT1576 LT1578 LT1616 LT1676/LT1776 LTC1765 LTC1877 LTC1878 LTC3401 LTC3402 LTC3404 DESCRIPTION High Efficiency DC/DC Converter High Efficiency DC/DC Converter 500kHz 1MHz High Efficiency 1.5A Switching Regulators High Efficiency Step-Down Switching Regulator 1.5A Step-Down Switching Regulators 1.5A Step-Down Switching Regulator 1.5A Step-Down Switching Regulator 1.5A Step-Down Switching Regulator 600mA Step-Down Switching Regulator Wide Input Range Step-Down Switching Regulators 1.25MHz, Wide Input Range Step-Down DC/DC High Efficiency Monolithic Step-Down Regulator High Efficiency Monolithic Step-Down Regulator Single Cell, High Current (1A), Micropower, Synchronous 3MHz Step-Up DC/DC Converter Single Cell, High Current (2A), Micropower, Synchronous 3MHz Step-Up DC/DC Converter 1.4MHz High Efficiency, Monolithic Synchronous Step-Down Regulator COMMENTS 42V, 500kHz Switch 35V, 500kHz Switch Boost Topology 25V, 4.5A, 500kHz Switch 500kHz, Synchronizable SO-8 Package 500kHz, Input, SO-8 Package 200kHz, Reduced Generation 200kHz, Reduced Generation 1.4MHz, Input, SOT-23 Package Input, 700mA Internal Switches 25V, SO-8 TSSOP-16E Packages 550kHz, MS8, 10V, =10µA, IOUT 600mA 550kHz, MS8, 10µA, IOUT 600mA 3.3V 0.5V Efficiency Synchronizable Oscillator from 100kHz 3MHz 0.7V Efficiency Synchronizable Oscillator from 100kHz 3MHz Efficiency, 100% Duty Cycle, 10µA, 2.65V
Burst Mode trademark Linear Technology Corporation.
sn1767 1767fas
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, 95035-7417
(408) 432-1900 FAX: (408) 434-0507
0.254 (.010)
DETAIL
4.88 (.192 .004)
3.00 0.102 (.118 .004) NOTE
SEATING PLANE
0.22 0.38 (.009 .015)
0.65 (.0256)
0.13 0.05 (.005 .002)
MSOP (MS8E) 0102
LT/TP 0302 PRINTED
www.linear.com
LINEAR TECHNOLOGY CORPORATION 1999

DESCRIPTIO 1.5A Switch Small MSOP Package Constant 1.25MHz Switch

Top Searches for this datasheet

Other recent searches