UC3842

Current ModePWMController

FEATURES•••••••••••

Optimized For Off-line And DCTo DC Converters

Low Start Up Current (<1mA)Automatic Feed ForwardCompensation

Pulse-by-pulse Current LimitingEnhanced Load ResponseCharacteristics

Under-voltage Lockout WithHysteresis

Double Pulse SuppressionHigh Current Totem PoleOutput

Internally TrimmedBandgapReference500khz OperationLow ROError Amp

DESCRIPTION

TheUC1842/3/4/5familyofcontrolICsprovidesthenecessaryfeaturestoimplementoff-lineorDCtoDCfixedfrequencycurrentmodecontrolschemeswithaminimalexternalpartscount.Internallyimplementedcircuitsincludeunder-voltagelockoutfeaturingstartupcurrentlessthan1mA,aprecisionreferencetrimmedforaccuracyattheerrorampinput,logictoinsurelatchedoperation,aPWMcomparatorwhichalsoprovidescurrentlimitcontrol,andatotempoleoutputstagedesignedtosourceorsinkhighpeakcurrent.Theoutput stage, suitable for driving N ChannelMOSFETs, is low in the off state.Differencesbetweenmembersofthisfamilyaretheunder-voltagelockoutthresholdsandmaximumdutycycleranges.TheUC1842andUC1844haveUVLOthresholdsof16V(on)and10V(off),ideallysuitedtooff-lineapplications.ThecorrespondingthresholdsfortheUC1843andUC1845are8.4Vand7.6V.TheUC1842andUC1843canoperatetodutycyclesapproaching100%.Arangeofzeroto50%isobtainedbytheUC1844andUC1845bytheadditionofaninternaltoggleflipflopwhichblankstheoutputoff every other clock cycle.

BLOCK DIAGRAM

Note 1:A/BNote 2:A =DIL-8Pin Number.B = SO-14 andCFP-14Pin Number.Toggle flip flop used only in 1844 and 1845.SLUS223A - APRIL 1997 - REVISED MAY 2002UC1842/3/4/5UC2842/3/4/5UC3842/3/4/5

ABSOLUTE MAXIMUM RATINGS(Note 1)

Supply Voltage (Low Impedance Source). . . . . . . . . . . . . .30VSupply Voltage (ICC< 30mA). . . . . . . . . . . . . . . . .Self LimitingOutput Current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .±1AOutput Energy (Capacitive Load). . . . . . . . . . . . . . . . . . . . .5µJAnalog Inputs (Pins 2, 3). . . . . . . . . . . . . . . . . . .-0.3V to +6.3VError Amp Output Sink Current. . . . . . . . . . . . . . . . . . . .10mAPower Dissipation at TA≤25°Χ(DIL−8)..................1ΩPower Dissipation at TA≤25°C (SOIC-14). . . . . . . . . .725mWStorage Temperature Range. . . . . . . . . . . . . .-65°C to +150°CLead Temperature (Soldering, 10 Seconds). . . . . . . . . .300°CNote 1:All voltages are with respect to Pin 5.All currents are positive into the specified terminal.Consult Packaging Section ofDatabookfor thermallimitations and considerations of packages.CONNECTION DIAGRAMSDIL-8,SOIC-8(TOP VIEW)N or J Package,D8 PackagePLCC-20(TOP VIEW)Q PackagePACKAGE PIN FUNCTIONFUNCTIONPIN1N/CCOMP2N/CN/CVFBN/CISENSEN/CN/CRT/CTN/CPWRGNDGROUNDN/COUTPUTN/CVCVCCN/CVREFSOIC-14,CFP-14.(TOP VIEW)D or W Package34567891011121314151617181920DISSIPATION RATING TABLE

PackageW

TA≤25°CPower Rating700mW

Derating FactorAbove TA≤25°C5.5mW/°C

TA≤70°CPower Rating452mW

TA≤85°CPower Rating370mW

TA≤125°CPower Rating150mW

2

UC1842/3/4/5UC2842/3/4/5UC3842/3/4/5

ELECTRICAL CHARACTERISTICS:

Unlessotherwisestated,thesespecificationsapplyfor-55°C≤TA≤125°Cforthe

UC184X;-40°C≤TA≤85°CfortheUC284X;0°C≤TA≤70°Cforthe384X;VCC=15V(Note5);RT=10k;CT=3.3nF,TA=TJ.TEST CONDITIONS

UC1842/3/4/5UC2842/3/4/5MIN

Reference SectionOutput VoltageLine RegulationLoad RegulationTemp. StabilityTotal Output VariationOutput Noise VoltageLong Term StabilityOutput Short CircuitOscillator SectionInitial AccuracyVoltage StabilityTemp. StabilityAmplitudeError Amp SectionInput VoltageInput Bias CurrentAVOL

Unity Gain BandwidthPSRR

Output Sink CurrentOutput Source CurrentVOUTHighVOUTLow

Current Sense SectionGain

Maximum Input SignalPSRR

Input Bias CurrentDelay to Output

VPIN3= 0 to 2V (Note 2)(Notes 3 and 4)VPIN1= 5V (Note 3)

12≤VCC≤25V (Note 3) (Note 2)

2.850.9

3170-2150

-103003.151.1

2.850.9

3170-2150

-103003.151.1

V/VVdBµAns

2≤VO≤4V(Note 2)TJ= 25°C12≤VCC≤25V

VPIN2= 2.7V,VPIN1= 1.1VVPIN2= 2.3V,VPIN1= 5VVPIN2= 2.3V,RL= 15k to groundVPIN2= 2.7V,RL= 15k to Pin 8

650.7602-0.55

VPIN1= 2.5V

2.45

2.50-0.3901706-0.860.7

1.12.55-1

650.7602-0.552.42

2.50-0.3901706-0.860.7

1.12.58-2

VµAdBMHzdBmAmAVV

TJ= 25°C (Note 6)12≤VCC≤25V

TMIN≤TA≤TMAX(Note 2)VPIN4peak to peak (Note 2)

47

520.251.7

571

47

520.251.7

571

kHz%%V

TJ= 25°C, IO= 1mA12≤VIN≤25V1≤I0≤20mA(Note 2) (Note 7)

Line, Load, Temp. (Note 2)

10Hz≤f≤10kHz,TJ= 25°C (Note2)TA= 125°C, 1000Hrs. (Note 2)

-304.9

505-100

25-180

-30

4.95

5.00660.2

5.0520250.45.1

4.82

505-100

25-180

4.90

5.00660.2

5.1020250.45.18

VmVmVmV/°CVµVmVmA

TYP

MAX

UC3842/3/4/5MIN

TYP

MAX

UNITS

PARAMETER

Note 2:Note 3:Note 4:Note 5:Note 6:Note 7:These parameters, although guaranteed, are not 100% tested in production.Parameter measured at trip point of latch withVPIN2= 0.Gain defined as∆VPIN1A=,0≤VPIN3≤08.V∆VPIN3AdjustVCCabove the start threshold before setting at 15V.Output frequency equals oscillator frequency for the UC1842 and UC1843.Output frequency is one half oscillator frequency for the UC1844 and UC1845.Temperature stability, sometimes referred to as average temperature coefficient, is described by the equation:V(max)−VREF(min)

TempStability=REFTJ(max)−TJ(min)

VREF(max) andVREF(min) are the maximum and minimum reference voltages measured over the appropriatetemperature range.Note that the extremes in voltage do not necessarily occur at the extremes in temperature.3

UC1842/3/4/5UC2842/3/4/5UC3842/3/4/5

ELECTRICAL CHARACTERISTICS:

Unlessotherwisestated,thesespecificationsapplyfor−55°C≤TA≤125°CfortheUC184X;−40°C≤TA≤85°CfortheUC284X;0°C≤TA≤70°Cforthe384X;VCC=15V(Note5);RT=10k;CT=3.3nF,TA=TJ.TEST CONDITION

UC1842/3/4/5UC2842/3/4/5MIN

Output SectionOutput Low LevelOutput High LevelRise TimeFall Time

Under-voltage Lockout SectionStart ThresholdMin. Operating VoltageAfter Turn OnPWMSection

Maximum Duty CycleMinimum Duty CycleTotal Standby CurrentStart-Up Current

Operating Supply Current

VPIN2=VPIN3= 0V

0.511

117

30

0.51134

117

mAmAV

X842/3X844/5

9546

9748

100500

9547

9748

100500

%%%

X842/4X843/5X842/4X843/5

157.897.0

168.4107.6

179.0118.2

14.57.88.57.0

168.4107.6

17.59.011.58.2

VVVV

ISINK= 20mAISINK= 200mAISOURCE= 20mAISOURCE= 200mA

TJ= 25°C, CL= 1nF (Note 2)TJ= 25°C, CL= 1nF (Note 2)

1312

0.11.513.513.55050

1501500.42.2

1312

0.11.513.513.55050

1501500.42.2

VVVVnsns

TYP

MAX

UC3842/3/4/5MIN

TYP

MAX

UNITS

PARAMETER

ICC= 25mA3034VCCZenerVoltage

Note 2:These parameters, although guaranteed, are not 100% tested in production.Note 3:Parameter measured at trip point of latch withVPIN2= 0.∆VPIN1

Note 4:Gain defined as:A=;0≤VPIN3≤08.V.∆VPIN3

Note 5:AdjustVCCabove the start threshold before setting at 15V.Note 6:Output frequency equals oscillator frequency for the UC1842 and UC1843.Output frequency is one half oscillator frequency for the UC1844 and UC1845.ERROR AMP CONFIGURATIONError Amp can Source or Sink up to 0.5mA4

UC1842/3/4/5UC2842/3/4/5UC3842/3/4/5

UNDER-VOLTAGE LOCKOUTDuringunder-voltagelock-out,theoutputdriverisbiasedtosinkminoramountsofcurrent.Pin6shouldbeshuntedtogroundwithableederresistortopreventactivatingthepowerswitchwithextraneousleakagecurrents.CURRENT SENSE CIRCUITPeak Current (IS) is Determined By The FormulaISMAX′RSA small RC filter may be required to suppress switch transients.OSCILLATOR SECTION5

UC1842/3/4/5UC2842/3/4/5

OUTPUT SATURATION CHARACTERISTICS

ERROR AMPLIFIER OPEN-LOOPFREQUENCY RESPONSE

OPEN-LOOP LABORATORY FIXTUREHighpeakcurrentsassociatedwithcapacitiveloadsne-cessitatecarefulgroundingtechniques.Timingandby-passcapacitorsshouldbeconnectedclosetopin5inasinglepointground.Thetransistorand5kpotentiometerareusedtosampletheoscillatorwaveformandapplyan adjustable ramp to pin 3.SHUT DOWN TECHNIQUES

ShutdownoftheUC1842canbeaccomplishedbytwomethods;eitherraisepin3above1Vorpullpin1belowavoltagetwodiodedropsaboveground.EithermethodcausestheoutputofthePWMcomparatortobehigh(refertoblockdiagram).ThePWMlatchisresetdomi-nantsothattheoutputwillremainlowuntilthenext6

clockcycleaftertheshutdownconditionatpin1and/or3isremoved.Inoneexample,anexternallylatchedshutdownmaybeaccomplishedbyaddinganSCRwhichwillberesetbycyclingVCCbelowthelowerUVLOthreshold.Atthispointthereferenceturnsoff,al-lowing theSCRto reset.UC1842/3/4/5UC2842/3/4/5UC3842/3/4/5

OFFLINEFLYBACKREGULATOR

Power Supply Specifications1.Input Voltages2.Line Isolation3.Switching Frequency5VAC to 130VA(50 Hz/60Hz)3750V40kHz5.Output Voltage:A.+5V,±5%;1A to 4A loadRipple voltage:50mV P-P MaxB.+12V,±3%;0.1A to 0.3A loadRipple voltage:100mV P-P MaxC.-12V ,±3%;0.1A to 0.3A loadRipple voltage:100mV P-P Max4.Efficiency at Full Load 70%SLOPE COMPENSATION

Afractionoftheoscillatorrampcanberesistivelysummedwiththecurrentsensesignaltoprovideslopecompensationforconvertersrequiringdutycycles over 50%.7

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