LP2951-50D中文资料

FEATURESOUTPUTGNDINPUT12348765INPUTFEEDBACKV TAPERROROUTPUTSENSESHUTDOWNGNDLP2951...D (SOIC) PACKAGE(TOP VIEW)LP2950...LP (TO-226/TO-92 PACKAGE(BOTTOM VIEW)DESCRIPTION/ORDERING INFORMATIONWITH SHUTDOWNSLVS582D–APRIL2006–REVISED MARCH2007•Wide Input Range…up to30V•Stable With Low ESR(>12mΩ)Capacitors •Rated Output Current of100mA•Current-and Thermal-Limiting Features •Low Dropout…380mV(Typ)at100mA•LP2950Only(3-Pin Package)•Low Quiescent Current…75µA(Typ)–Fixed-Output Voltages of5V,3.3V,and3V•Tight Line Regulation…0.03%(Typ)•LP2951Only(8-Pin Package)•Tight Load Regulation…0.04%(Typ)–Fixed-or Adjustable-Output Voltages:•High V O Accuracy5V/ADJ,3.3V/ADJ,and3V/ADJ – 1.4%at25°C–Low-Voltage Error Signal on Falling Output –2%Over Temperature–Shutdown Capability•Can Be Used as a Regulator or Reference–Remote Sense Capability for OptimalOutput Regulation and AccuracyThe LP2950and LP2951devices are bipolar,low-dropout voltage regulators that can accommodate a wide input supply-voltage range of up to30V.The easy-to-use,3-pin LP2950is available in fixed-output voltages of5V, 3.3V,and3V.However,the8-pin LP2951is able to output either a fixed or adjustable output from the same device.By tying the OUTPUT and SENSE pins together,and the FEEDBACK and V TAP pins together,the LP2951outputs a fixed5V,3.3V,or3V(depending on the version).Alternatively,by leaving the SENSE and V TAP pins open and connecting FEEDBACK to an external resistor divider,the output can be set to any value between1.235V to30V.The8-pin LP2951also offers additional functionality that makes it particularly suitable for battery-powered applications.For example,a logic-compatible shutdown feature allows the regulator to be put in standby mode for power savings.In addition,there is a built-in supervisor reset function in which the ERROR output goes low when V OUT drops by6%of its nominal value for whatever reasons–due to a drop in V IN,current limiting,or thermal shutdown.The LP2950and LP2951are designed to minimize all error contributions to the output voltage.With a tight output tolerance(0.5%at25°C),a very low output voltage temperature coefficient(20ppm typical),extremely good line and load regulation(0.3%and0.4%typical),and remote sensing capability,the parts can be used as either low-power voltage references or100-mA regulators.Please be aware that an important notice concerning availability,standard warranty,and use in critical applications of TexasInstruments semiconductor products and disclaimers thereto appears at the end of this data sheet.PRODUCTION DATA information is current as of publication date.Copyright©2006–2007,Texas Instruments Incorporated Products conform to specifications per the terms of the TexasInstruments standard warranty.Production processing does notnecessarily include testing of all parameters.WITH SHUTDOWNSLVS582D–APRIL 2006–REVISED MARCH 2007ORDERING INFORMATION (1)V OUT ORDERABLE T APACKAGE (2)TOP-SIDE MARKING (NOM)PART NUMBER Bulk of 1000LP2950-30LP TO-226/TO-92–LPKY5030Reel of 2000LP2950-30LPR 3VTube of 75LP2951-30D SOIC –DKY5130Reel of 2500LP2951-30DR Bulk of 1000LP2950-33LP TO-226/TO-92–LPKY5033Reel of 2000LP2950-33LPR 3.3VTube of 75LP2951-33D –40°C to 125°CSOIC –DKY5133Reel of 2500LP2951-33DR Bulk of 1000LP2950-50LP PREVIEW TO-226/TO-92–LPReel of 2000LP2950-50LPR KY50505VTube of 75LP2951-50D SOIC –DKY5150Reel of 2500LP2951-50DR Tube of 75LP2951D ADJSOIC-DKY5150Reel of 2500LP2951DR(1)For the most current package and ordering information,see the Package Option Addendum at the end of this document,or see the TI website at .(2)Package drawings,standard packing quantities,thermal data,symbolization,and PCB design guidelines are available at /sc/package .2Submit Documentation FeedbackWITH SHUTDOWNSLVS582D–APRIL 2006–REVISED MARCH 2007LP2950FUNCTIONAL BLOCK DIAGRAMLP2951FUNCTIONAL BLOCK DIAGRAM3Submit Documentation FeedbackAbsolute Maximum Ratings (1)Recommended Operating ConditionsWITH SHUTDOWNSLVS582D–APRIL 2006–REVISED MARCH 2007over operating free-air temperature range (unless otherwise noted)MINMAX UNIT V IN Continuous input voltage range –0.330V V SHDN SHUTDOWN input voltage range–1.530V ERROR comparator output voltage range (2)–1.530V V FDBK FEEDBACK input voltage range (2)(3)–1.530V D package 97θJA Package thermal impedance (4)(5)°C/W LP package140T J Operating virtual junction temperature 150°C T stg Storage temperature range–65150°C(1)Stresses beyond those listed under "absolute maximum ratings"may cause permanent damage to the device.These are stress ratings only,and functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions"is not implied.Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.(2)May exceed input supply voltage(3)If load is returned to a negative power supply,the output must be diode clamped to GND.(4)Maximum power dissipation is a function of T J (max),θJA ,and T A .The maximum allowable power dissipation at any allowable ambient temperature is P D =(T J (max)–T A )/θJA .Operating at the absolute maximum T J of 150°C can affect reliability.(5)The package thermal impedance is calculated in accordance with JESD 51-7.MINMAX UNIT V IN Supply input voltage(1)30V T J Operating virtual junction temperature–40125°C(1)Minimum V IN is the greater of:a.2V (25°C),2.3V (over temperature),orb.V OUT(MAX)+Dropout (Max)at rated I L4Submit Documentation FeedbackElectrical CharacteristicsWITH SHUTDOWN SLVS582D–APRIL2006–REVISED MARCH2007V IN =VOUT(nominal)+1V,IL=100µA,CL=1µF(5-V versions)or CL=2.2µF(3-V and3.3-V versions),8-pin version:FEEDBACK tied to VTAP ,OUTPUT tied to SENSE,VSHUTDOWN≤0.7VPARAMETER TEST CONDITIONS T J MIN TYP MAX UNIT3-V VERSION(LP295x-30)25°C 2.9703 3.030V OUT Output voltage I L=100µA V–40°C to125°C 2.9403 3.0603.3-V VERSION(LP295x-33)25°C 3.267 3.3 3.333V OUT Output voltage I L=100µA V–40°C to125°C 3.234 3.3 3.3665-V VERSION(LP295x-50)25°C 4.9505 5.050V OUT Output voltage I L=100µA V–40°C to125°C 4.9005 5.100ALL VOLTAGE OPTIONSOutput voltage temperatureI L=100µA–40°C to125°C20100ppm/°Ccoefficient(1)25°C0.030.2 Line regulation(2)V IN=[V OUT(NOM)+1V]to30V%/V–40°C to125°C0.425°C0.040.2 Load regulation(2)I L=100µA to100mA%–40°C to125°C0.325°C5080I L=100µA–40°C to125°C150V IN–V OUT Dropout voltage(3)mV25°C380450I L=100mA–40°C to125°C60025°C75120I L=100µAµA–40°C to125°C140I GND GND current25°C812I L=100mA mA–40°C to125°C1425°C110170V IN=V OUT(NOM)–0.5V,Dropout ground currentµAI L=100µA–40°C to125°C20025°C160200 Current limit V OUT=0V mA–40°C to125°C220 Thermal regulation(4)I L=100µA25°C0.050.2%/WC L=1µF(5V only)430C L=200µF160Output noise(RMS),25°CµVLP2951-50:C L=3.3µF,10Hz to100kHzC Bypass=0.01µF between pins1100and7(LP2951-xx)8-PIN VERSION ONLY ADJ25°C 1.218 1.235 1.252–40°C to125°C 1.212 1.257Reference voltage VV OUT=V REF to(V IN–1V),V IN=2.3V to30V,–40°C to125°C 1.200 1.272I L=100µA to100mAReference voltage25°C20ppm/°C temperature coefficient(1)(1)Output or reference voltage temperature coefficient is defined as the worst-case voltage change divided by the total temperature range.(2)Regulation is measured at constant junction temperature,using pulse testing with a low duty cycle.Changes in output voltage due toheating effects are covered under the specification for thermal regulation.(3)Dropout voltage is defined as the input-to-output differential at which the output voltage drops100mV,below the value measured at1-Vdifferential.The minimum input supply voltage of2V(2.3V over temperature)must be observed.(4)Thermal regulation is defined as the change in output voltage at a time(T)after a change in power dissipation is applied,excluding loador line regulation effects.Specifications are for a50-mA load pulse at V IN=30V,V OUT=5V(1.25-W pulse)for t=10ms.5Submit Documentation FeedbackWITH SHUTDOWNSLVS582D–APRIL 2006–REVISED MARCH 2007Electrical Characteristics (continued)V IN =V OUT (nominal)+1V,I L =100µA,C L =1µF (5-V versions)or C L =2.2µF (3-V and 3.3-V versions),8-pin version:FEEDBACK tied to V TAP ,OUTPUT tied to SENSE,V SHUTDOWN ≤0.7VPARAMETER TEST CONDITIONST J MINTYP MAX UNIT 25°C 2040FEEDBACK bias current nA –40°C to 125°C60FEEDBACK bias current 25°C0.1nA/°Ctemperature coefficientERROR COMPARATOR25°C 0.011Output leakage current V OUT =30VµA –40°C to 125°C225°C 150250V IN =V OUT(NOM)–0.5V,Output low voltage mV I OL =400µA–40°C to 125°C40025°C 4060Upper threshold voltage mV (ERROR output high)(5)–40°C to 125°C2525°C 7595Lower threshold voltage mV (ERROR output low)(5)–40°C to 125°C140Hysteresis (6)25°C15mVSHUTDOWN INPUTLow (regulator ON)0.7Input logic voltage–40°C to 125°CVHigh (regulator OFF)225°C 3050V TAP =2.4V–40°C to 125°C100SHUTDOWN input currentµA 25°C 450600V TAP =30V–40°C to 125°C750V SHUTDOWN ≥2V,25°C 310Regulator output current V IN ≤30V,V OUT =0,µA in shutdown–40°C to 125°C20FEEDBACK tied to V TAP(5)Comparator thresholds are expressed in terms of a voltage differential equal to the nominal reference voltage (measured atV IN –V OUT =1V)minus FEEDBACK terminal voltage.To express these thresholds in terms of output voltage change,multiply by the error amplifier gain =V OUT /V REF =(R1+R2)/R2.For example,at a programmed output voltage of 5V,the ERROR output is specified to go low when the output drops by 95mV ×5V/1.235V =384mV.Thresholds remain constant as a percentage of V OUT (as V OUT is varied),with the low-output warning occurring at 6%below nominal (typ)and 7.7%(max).(6)Comparator thresholds are expressed in terms of a voltage differential equal to the nominal reference voltage (measured atV IN –V OUT =1V)minus FEEDBACK terminal voltage.To express these thresholds in terms of output voltage change,multiply by the error amplifier gain =V OUT /V REF =(R1+R2)/R2.For example,at a programmed output voltage of 5V,the ERROR output is specified to go low when the output drops by 95mV ×5V/1.235V =384mV.Thresholds remain constant as a percentage of V OUT (as V OUT is varied),with the low-output warning occurring at 6%below nominal (typ)and 7.7%(max).6Submit Documentation FeedbackTYPICALCHARACTERISTICS0.010.11100.00010.0010.010.1I L –Load Current –AQ u i e s c e n t C u r r e n t –m A0102030405060708090100V IN –Input Voltage –VI n p u t C u r r e n t –µA020406080100120140160180200012345678910V IN –Input Voltage –VI n p u t C u r r e n t –µA010203040506070809010011012012345678910V IN –Input Voltage –VI n p u t C u r r e n t –m AWITH SHUTDOWNSLVS582D–APRIL 2006–REVISED MARCH 2007QUIESCENT CURRENTINPUT CURRENTvsvsLOAD CURRENTINPUT VOLTAGEINPUT CURRENTINPUT CURRENTvsvsINPUT VOLTAGEINPUT VOLTAGE7Submit Documentation Feedback4.9004.9254.9504.9755.0005.0255.0505.0755.100-40-25-105203550658095110125T A –Temperature –°C V O U T –O u t p u t V o l t a g e –V102030405060708090100110120V IN –Input Voltage –VQ u i e s c e n t C u r r e n t –µA12345678012345678V IN –Input Voltage –VQ u i e s c e n t C u r r e n t –µA0102030405060708090100110120012345678V IN –Input Voltage –VQ u i e s c e n t C u r r e n t –µAWITH SHUTDOWNSLVS582D–APRIL 2006–REVISED MARCH 2007TYPICAL CHARACTERISTICS (continued)OUTPUT VOLTAGEQUIESCENT CURRENTvsvsTEMPERATUREINPUT VOLTAGEQUIESCENT CURRENTQUIESCENT CURRENTvsvsINPUT VOLTAGEINPUT VOLTAGE8Submit Documentation Feedback50556065707580859095100-40-25-105203550658095110125T A –Temperature –°CQ u i e s c e n t C u r r e n t –µA55.566.577.588.599.510-40-25-105203550658095110125T A –Temperature –°CQ u i e s c e n t C u r r e n t –mA5075100125150175200225250-40-25-105203550658095110125T A –Temperature –°CS h o r t -C i r c u i t C u r r e n t –A50100150200250300350400450500-40-25-105203550658095110125T A –Temperature –°C(V I N –V O U T )–D r o p o u t V o l t a g e –m VWITH SHUTDOWNSLVS582D–APRIL 2006–REVISED MARCH 2007TYPICAL CHARACTERISTICS (continued)QUIESCENT CURRENTQUIESCENT CURRENTvsvsTEMPERATURETEMPERATURESHORT-CIRCUIT CURRENTDROPOUT VOLTAGEvsvsTEMPERATURETEMPERATURE9Submit Documentation Feedback1.61.651.71.751.81.851.91.952-40-25-105203550658095110125T A –Temperature –°CM i n i m u m O p e r a t i n g V o l t a g e –V501001502002503003504000.00010.0010.010.1I O –Output Current –A (V I N –V O U T )–D r o p o u t V o l t a g e –m V012345678012345678V IN –Input Voltage –VE R R O R O u t p u t –V-20-15-10-5051015202530-55-30-520457095120145T A –Temperature –°CF E E D B A C K B i a s C u r r e n t –n AWITH SHUTDOWNSLVS582D–APRIL 2006–REVISED MARCH 2007TYPICAL CHARACTERISTICS (continued)DROPOUT VOLTAGELP2951MINIMUM OPERATING VOLTAGEvsvsOUTPUT CURRENTTEMPERATURELP2951FEEDBACK BIAS CURRENTLP2951ERROR COMPARATOR OUTPUTvsvsTEMPERATUREINPUT VOLTAGE10Submit Documentation FeedbackInput Voltage2V/divOutput Voltage80 mV/div00.250.50.7511.251.51.75200.10.20.30.40.50.60.70.80.9V OL –Output Low Voltage –VI S I N K –S i n k C u r r e n t –m AOutput Load 100 mA/divOutput Voltage100 mV/divOutput Load 100 mA/divOutput Voltage100 mV/divLP2950,LP2951ADJUSTABLE MICROPOWER VOLTAGE REGULATORSWITH SHUTDOWNSLVS582D–APRIL 2006–REVISED MARCH 2007TYPICAL CHARACTERISTICS (continued)LP2951ERROR COMPARATOR SINK CURRENTLINE TRANSIENT RESPONSEvsvs OUTPUT LOW VOLTAGETIMELOAD TRANSIENT RESPONSELOAD TRANSIENT RESPONSEvs vs TIMETIME(V OUT =5V,C L =1µF)(V OUT =5V,C L =10µF)20304050607080901.E+011.E+021.E+031.E+041.E+051.E+06f –Frequency –HzP o w e r -S u p p l y R i p p l e R e j e c t i o n –d B101001k 10k 100k1M 0.010.11101001.E+011.E+02 1.E+03 1.E+04 1.E+05 1.E+06f –Frequency –HzO u t p u t I m p e d a n c e –Oh m 101001k 10k 100k 1M ΩLP2950,LP2951ADJUSTABLE MICROPOWER VOLTAGE REGULATORS WITH SHUTDOWNSLVS582D–APRIL 2006–REVISED MARCH 2007TYPICAL CHARACTERISTICS (continued)ENABLE TRANSIENT RESPONSEENABLE TRANSIENT RESPONSEvs vs TIMETIME(C L =1µF,I L =1mA)(C L =10µF,I L =1mA)OUTPUT IMPEDANCERIPPLE REJECTIONvsvsFREQUENCYFREQUENCY1020304050607080901001.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06f –Frequency –HzP o w e r -S u p p l y R i p p l e R e j e c t i o n –d B101001k10k100k1M1020304050607080901001.E+011.E+02 1.E+03 1.E+04 1.E+05 1.E+06f –Frequency –HzP o w e r -S u pp l y R i p p l e R e j e c t i o n –d B101001k 10k 100k 1M 050100150200250300350400-40-25-105203550658095110125T A –Temperature –°CR P 2P 4–P i n 2t o P i n 4R e s i s t a n c e –k W1234561.E+01 1.E+02 1.E+03 1.E+04 1.E+05f –Frequency –HzO u t p u t N o i s e –µVµF µF 101001k10k100kLP2950,LP2951ADJUSTABLE MICROPOWER VOLTAGE REGULATORSWITH SHUTDOWNSLVS582D–APRIL 2006–REVISED MARCH 2007TYPICAL CHARACTERISTICS (continued)RIPPLE REJECTIONRIPPLE REJECTIONvsvsFREQUENCYFREQUENCYLP2951OUTPUT NOISELP2951DIVIDER RESISTANCEvsvsFREQUENCYTEMPERATURE0.80.911.11.21.31.41.51.61.7-40-25-105203550658095110125T A–Temperature–°CInputLogicVoltage(OFFtoON)–V0.80.911.11.21.31.41.51.61.7-40-25-105203550658095110125T A–Temperature–°CInputLogicVoltage(ONtoOFF)–V-2-11234560510********V IN–Input Voltage–VOutputVoltageChange–mVLP2950,LP2951ADJUSTABLE MICROPOWER VOLTAGE REGULATORSWITH SHUTDOWNSLVS582D–APRIL2006–REVISED MARCH2007TYPICAL CHARACTERISTICS(continued)SHUTDOWN THRESHOLD VOLTAGE(OFF TO ON)SHUTDOWN THRESHOLD VOLTAGE(ON TO OFF)vs vsTEMPERATURE TEMPERATURELINE REGULATIONvsINPUT VOLTAGEAPPLICATION INFORMATION Input Capacitor(C IN)Output Capacitor(C OUT)Capacitance ValueESR Range LP2950,LP2951ADJUSTABLE MICROPOWER VOLTAGE REGULATORSWITH SHUTDOWNSLVS582D–APRIL2006–REVISED MARCH2007A1-µF(tantalum,ceramic,or aluminum)electrolytic capacitor should be placed locally at the input of the LP2950or LP2951if there is,or will be,significant impedance between the ac filter capacitor and the input;for example,if a battery is used as the input or if the ac filter capacitor is located more than10in away.There are no ESR requirements for this capacitor,and the capacitance can be increased without limit.As with most PNP LDOs,stability conditions require the output capacitor to have a minimum capacitance and an ESR that falls within a certain range.For V OUT≥5V,a minimum of1µF is required.For lower V OUT,the regulator’s loop gain is running closer to unity gain and,thus,has lower phase margins.Consequently,a larger capacitance is needed for stability.For V OUT=3V or3.3V,a minimum of2.2µF is recommended.For worst case,V OUT=1.23V(using the ADJ version),a minimum of3.3µF is recommended.C OUT can be increased without limit and only improves the regulator stability and transient response.Regardless of its value,the output capacitor should have a resonant frequency less than500kHz.The minimum capacitance values given above are for maximum load current of100mA.If the maximum expected load current is less than100mA,then lower values of C OUT can be used.For instance,if I OUT<10 mA,then only0.33µF is required for C OUT.For I OUT<1mA,0.1µF is sufficient for stability requirements.Thus, for a worst-case condition of100-mA load and V OUT=V REF=1.235V(representing the highest load current and lowest loop gain),a minimum C OUT of3.3µF is recommended.For the LP2950,no load stability is inherent in the design—a desirable feature in CMOS circuits that are put in standby(such as RAM keep-alive applications).If the LP2951is used with external resistors to set the output voltage,a minimum load current of1µA is recommended through the resistor divider.The regulator control loop relies on the ESR of the output capacitor to provide a zero to add sufficient phase margin to ensure unconditional regulator stability;this requires the closed-loop gain to intersect the open-loop response in a region where the open-loop gain rolls off at20dB/decade.This ensures that the phase always is less than180°(phase margin greater than0°)at unity gain.Thus,a minimum-maximum range for the ESR must be observed.The upper limit of this ESR range is established by the fact that too high an ESR could result in the zero occurring too soon,causing the gain to roll off too slowly,which,in turn allows a third pole to appear before unity gain and introduce enough phase shift to cause instability.This typically limits the max ESR to approximately 5Ω.Conversely,the lower limit of the ESR is tied to the fact that too low an ESR shifts the zero too far out(past unity gain)and,thus,allows the gain to roll off at40dB/decade at unity gain,with a resulting phase shift of greater than180°.Typically,this limits the minimum ESR to approximately20mΩto30mΩ.For specific ESR requirements,see Typical Characteristics.Capacitor TypesC BYPASS :Noise and Stability Improvementf (CBYPASS)]200Hz ³C BYPASS +12p R1 200Hz (1)ERROR Function (LP2951Only)LP2950,LP2951ADJUSTABLE MICROPOWER VOLTAGE REGULATORS WITH SHUTDOWNSLVS582D–APRIL 2006–REVISED MARCH 2007APPLICATION INFORMATION (continued)Most tantalum or aluminum electrolytics are suitable for use at the input.Film-type capacitors also work,but at higher cost.When operating at low temperature,care should be taken with aluminum electrolytics,as their electrolytes often freeze at –30°C.For this reason,solid tantalum capacitors should be used at temperatures below –25°C.Ceramic capacitors can be used,but due to their low ESR (as low as 5m Ωto 10m Ω),they may not meet the minimum ESR requirement previously discussed.If a ceramic capacitor is used,a series resistor between 0.1Ωto 2Ωmust be added to meet the minimum ESR requirement.In addition,ceramic capacitors have one glaring disadvantage that must be taken into account —a poor temperature coefficient,where the capacitance can vary significantly with temperature.For instance,a large-value ceramic capacitor (≥2.2µF)can lose more than half of its capacitance as temperature rises from 25°C to 85°C.Thus,a 2.2-µF capacitor at 25°C drops well below the minimum C OUT required for stability as ambient temperature rises.For this reason,select an output capacitor that maintains the minimum 2.2-µF required for stability for the entire operating temperature range.In the LP2951,an external FEEDBACK pin directly connected to the error amplifier noninverting input can allow stray capacitance to cause instability by shunting the error amplifier feedback to GND,especially at high frequencies.This is worsened if high-value external resistors are used to set the output voltage,because a high resistance allows the stray capacitance to play a more significant role;i.e.,a larger RC time delay is introduced between the output of the error amplifier and its FEEDBACK input,leading to more phase shift and lower phase margin.A solution is to add a 100-pF bypass capacitor (C BYPASS )between OUTPUT and FEEDBACK;because C BYPASS is in parallel with R1,it lowers the impedance seen at FEEDBACK at high frequencies,in effect offsetting the effect of the parasitic capacitance by providing more feedback at higher frequencies.More feedback forces the error amplifier to work at a lower loop gain,so C OUT should be increased to a minimum of 3.3µF to improve the regulator’s phase margin.C BYPASS can be also used to reduce output noise in the LP2951.This bypass capacitor reduces the closed loop gain of the error amplifier at the high frequency,so noise no longer scales with the output voltage.This improvement is more noticeable with higher output voltages,because loop gain reduction is greatest.A suitable C BYPASS is calculated as shown in Equation 1:On the 3-pin LP2950,noise reduction can be achieved by increasing the output capacitor,which causes theregulator bandwidth to be reduced,therefore,eliminating high-frequency noise.However,this method is relatively inefficient,as increasing C OUT from 1µF to 220µF only reduces the regulator’s output noise from 430µV to 160µV (over a 100-kHz bandwidth).The LP2951has a low-voltage detection comparator that outputs a logic low when the output voltage drops by ≈6%from its nominal value,and outputs a logic high when V OUT has reached ≈95%of its nominal value.This 95%of nominal figure is obtained by dividing the built-in offset of ≈60mV by the 1.235-V bandgap reference,and remains independent of the programmed output voltage.For example,the trip-point threshold (ERROR output goes high)typically is 4.75V for a 5-V output and 11.4V for a 12-V output.Typically,there is a hysteresis of 15mV between the thresholds for high and low ERROR output.A timing diagram is shown in Figure 1for ERROR vs V OUT (5V),as V IN is ramped up and down.ERROR becomes valid (low)when V IN ≈1.3V.When V IN ≈5V,V OUT =4.75V,causing ERROR to go high.Because the dropout voltage is load dependent,the output trip-point threshold is reached at different values of V IN ,depending on the load current.For instance,at higher load current,ERROR goes high at a slightly higher value of V IN ,and vice versa for lower load current.The output-voltage trip point remains at ≈4.75V,regardless of the load.Note that when V IN ≤1.3V,the ERROR comparator output is turned off and pulled high to its pullup voltage.If V OUT is used as the pullup voltage,rather than an external 5-V source,ERROR typically is ≈1.2V.In this condition,an equal resistor divider (10k Ωis suitable)can be tied to ERROR to divide down the voltage to a valid logic low during any fault condition,while still enabling a logic high during normal operation.5 V1.3 VInput VoltageOutput VoltageERROR4.75 VProgramming Output Voltage (LP2951Only)V OUT +V REF ǒ1)R1R2Ǔ*I FB R 1(2)LP2950,LP2951ADJUSTABLE MICROPOWER VOLTAGE REGULATORSWITH SHUTDOWNSLVS582D–APRIL 2006–REVISED MARCH 2007APPLICATION INFORMATION (continued)Figure 1.ERROR Output TimingBecause the ERROR comparator has an open-collector output,an external pullup resistor is required to pull the output up to V OUT or another supply voltage (up to 30V).The output of the comparator is rated to sink up to 400µA.A suitable range of values for the pullup resistor is from 100k Ωto 1M Ω.If ERROR is not used,it can be left open.A unique feature of the LP2951is its ability to output either a fixed voltage or an adjustable voltage,depending on the external pin connections.To output the internally programmed fixed voltage,tie the SENSE pin to the OUTPUT pin and the FEEDBACK pin to the V TAP pin.Alternatively,a user-programmable voltage ranging from the internal 1.235-V reference to a 30-V max can be set by using an external resistor divider pair.The resistor divider is tied to V OUT ,and the divided-down voltage is tied directly to FEEDBACK for comparison against the internal 1.235-V reference.To satisfy the steady-state condition in which its two inputs are equal,the error amplifier drives the output to equal Equation 2:Where:V REF =1.235V applied across R2I FB =FEEDBACK bias current,typically 20nAA minimum regulator output current of 1µA must be maintained.Thus,in an application where a no-load condition is expected (for example,CMOS circuits in standby),this 1-µA minimum current must be provided by the resistor pair,effectively imposing a maximum value of R2=1.2M Ω(1.235V/1.2M Ω≈1µA).I FB =20nA introduces an error of ≈0.02%in V OUT .This can be offset by trimming R1.Alternatively,increasing the divider current makes I FB less significant,thus,reducing its error contribution.For instance,using R2=100k Ωreduces the error contribution of I FB to 0.17%by increasing the divider current to ≈12µA.This increase in the divider current still is small compared to the 600-µA typical quiescent current of the LP2951under no load.。