UC3845AD1资料

HIGH PERFORMANCE CURRENT MODE PWM CONTROLLERNOT FOR NEW DESIGN

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FEATURES

TRIMMED OSCILLATOR DISCHARGE CURRENT

CURRENT MODE OPERATION TO 500kHz AUTOMATIC FEED FORWARD COMPENSATION

LATCHING PWM FOR CYCLE-BY-CYCLE CURRENT LIMITING

INTERNALLY TRIMMED REFERENCE WITH UNDERVOLTAGE LOCKOUT

HIGH CURRENT TOTEM POLE OUTPUT UNDERVOLTAGE LOCKOUT WITH HYSTERESIS

LOW START-UP CURRENT (< 0.5mA) DOUBLE PULSE SUPPRESSION

Figure 1. Package

DIP-8SO-8Table 1. Order Codes

Part Number

UC2842AD1; UC3842AD1;UC2843AD1; UC3843AD1;UC2844AD1; UC3844AD1;UC2845AD1; UC3845AD1UC2842AN; UC3842AN;UC2843AN; UC3843AN;UC2844AN; UC3844AN;UC2845AN; UC3845AN

PackageSO-8

DIP-8

2DESCRIPTION

The UC384xA family of control ICs provides thenecessary features to implement off-line or DC toDC fixed frequency current mode control schemeswith a minimal external parts count. Internally im-plemented circuits include a trimmed oscillator forprecise DUTY CYCLE CONTROL under voltagelockout featuring start-up current less than 0.5mA,a precision reference trimmed for accuracy at theerror amp input, logic to insure latched operation,a PWM comparator which also provides currentlimit control, and a totem pole output stage de-signed to source or sink high peak current. Theoutput stage, suitable for driving N-Channel MOS-FETs, is low in the off-state.

Differences between members of this family arethe under-voltage lockout thresholds and maxi-mum duty cycle ranges. The UC3842A andUC3844A have UVLO thresholds of 16V (on) and10V (off), ideally suited off-line applications Thecorresponding thresholds for the UC3843A andUC3845A are 8.5 V and 7.9V. The UC3842A andUC3843A can operate to duty cycles approaching100%. A range of the zero to < 50 % is obtained bythe UC3844A and UC3845A by the addition of aninternal toggle flip flop which blanks the output offevery other clock cycle.

Figure 2. Block Diagram (toggle flip flop used only in UC3844A and UC3845A)

Vi734VGROUND5UVLOS/R5VREFINTERNALBIASVREF GOODLOGICRT/CT4OSC+-ERROR AMP.2RR1VSRCURRENTSENSECOMPARATORD95IN3318VREF5V 50mA2.50V6TOUTPUTVFBCOMPCURRENTSENSE213PWMLATCHMay 2004

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UC384XA - UC284XA

Table 2. Absolute Maximum Ratings

SymbolViViIOEOSupply Voltage (Ii < 30mA)Output Current

Output Energy (capacitive load)Analog Inputs (pins 2, 3)

Error Amplifier Output Sink Current

PtotPtotTstgTJTLPower Dissipation at Tamb ≤ 25 °C (DIP-8)Power Dissipation at Tamb ≤ 25 °C (SO-8)Storage Temperature RangeJunction Operating TemperatureLead Temperature (soldering 10s)

Parameter

Supply Voltage (low impedance source)

Value30Self Limiting

±15– 0.3 to 5.5

101.25800– 65 to 150– 40 to 150

300

AµJVmAWmW°C°C°CUnitV

* All voltages are with respect to pin 5, all currents are positive into the specified terminal.

Figure 3. DIP-8/SO-8 Pin Connection (Top view)

COMPVFBISENSERT/CT1234D95IN3328765VREFViOUTPUTGROUNDTable 3. Pin Description

N°12345678

PinCOMPVFBISENSERT/CTGROUNDOUTPUTVCCVrefFunction

This pin is the Error Amplifier output and is made available for loop compensation.

This is the inverting input of the Error Amplifier. It is normally connected to the switching power supply output through a resistor divider.

A voltage proportional to inductor current is connected to this input. The PWM uses this information to terminate the output switch conduction.

The oscillator frequency and maximum Output duty cycle are programmed by connecting resistor RT to Vref and cpacitor CT to ground. Operation to 500kHz is possible.This pin is the combined control circuitry and power ground.

This output directly drives the gate of a power MOSFET. Peak currents up to 1A are sourced and sunk by this pin.

This pin is the positive supply of the control IC.

This is the reference output. It provides charging current for capacitor CT through resistor RT.

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UC384XA - UC284XA

Table 4. Thermal Data

SymbolRth j-ambParameter

Thermal Resistance Junction-ambient

Max.

DIP-8100

SO-8150

Unit°C/W

Table 5. Electrical Characteristcs

( [note 1] Unless otherwise stated, these specifications apply for -25 < Tamb < 85°C for UC284XA;0 < Tamb < 70°C for UC384XA; Vi = 15V (note 5); RT = 10K; CT = 3.3nF)

Symbol

Parameter

Test Condition Tj = 25°C Io= 1mA12V ≤ Vi ≤ 25V1 ≤ Io ≤ 20mA(Note 2)

Line, Load, Temperature10Hz ≤ f ≤ 10KHzTj = 25°C (note 2)

Tamb

UC284XAMin. Typ.4.95

5.00230.2

4.9

505

-30

-100520.251.68.32.50-0.1650.7602-0.55

9017012-16.20.8

1.125-180571––8.82.55-1

650.7602-0.55-3047–––7.8

5.1Max.5.052025

UC384XAMin. Typ.4.90

5.00230.2

4.82

505-100520.251.68.32.50-0.19017012-16.20.8

1.125-180571––8.82.58-25.18Max.5.102025

Unit

REFERENCE SECTIONVREF∆VREF∆VREFOutput VoltageLine RegulationLoad RegulationTotal Output Variation

eNOutput Noise VoltageLong Term Stability

VmVmVmV/°CVµVmVmAKHz%%VmAVµAdBMHzdBmAmAVV

∆VREF/∆TTemperature Stability

= 125°C, 1000Hrs

(note 2)

ISC

fOSCOutput Short CircuitFrequency

Tj = 25°CVCC = 12V to 25VTA = Tlow to Thigh(peak to peak)TJ = 25°CVPIN1 = 2.5VVFB = 5V2V ≤ Vo ≤ 4VTJ = 25°C12V ≤ Vi ≤25VVPIN2 = 2.7VVPIN1= 1.1V

VPIN2 = 2.3V VPIN1 = 5VVPIN2 = 2.3V;RL = 15KΩ to Ground

VPIN2 = 2.7V;RL = 15KΩ to Pin 8(note 3 & 4)VPIN1 = 5V (note 3)12 ≤ Vi ≤ 25V (note 3)

OSCILLATOR SECTION

47–––7.82.45

∆fOSC/∆VFrequency Change with Volt.∆VREF/∆TFrequency Change with Temp.VOSCIdischgV2IbBWPSRRIoIoOscillator Voltage SwingDischarge Current (VOSC =2V)Input VoltageInput Bias CurrentAVOLUnity Gain BandwidthPower Supply Rejec. RatioOutput Sink CurrentOutput Source CurrentVOUT HighVOUT Low

CURRENT SENSE SECTIONGVV3SVRIbGain

Maximum Input SignalSupply Voltage RejectionInput Bias CurrentDelay to Output

2.850.9

3170-2150

-103003.151.1

2.850.9

3170-2150

-103003.151.1

V/VVdBµAns

ERROR AMP SECTION

2.42

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UC384XA - UC284XA

Table 5. Electrical Characteristcs (continued)

( [note 1] Unless otherwise stated, these specifications apply for -25 < Tamb < 85°C for UC284XA;0 < Tamb < 70°C for UC384XA; Vi = 15V (note 5); RT = 10K; CT = 3.3nF)

Symbol

Parameter

Test Condition

UC284XAMin. Typ.0.11.6

1312

13.513.50.75050

1.2150150Max.0.42.2

1312

UC384XAMin. Typ.0.11.613.513.50.75050

1.2150150Max.0.42.2

Unit

OUTPUT SECTIONVOLVOHVOLStrtfOutput Low LevelOutput High LevelUVLO SaturationRise TimeFall Time

ISINK = 20mAISINK = 200mAISOURCE = 20mAISOURCE = 200mAVCC = 6V; ISINK = 1mA Tj = 25°CCL = 1nF (2)Tj = 25°CCL = 1nF (2)UNDER-VOLTAGE LOCKOUT SECTION

Start ThresholdMin Operating Voltage

After Turn-on

PWM SECTION

Maximum Duty CycleMinimum Duty Cycle

TOTAL STANDBY CURRENT

IstStart-up Current

Vi = 6.5V for UCX843A/45A

Vi = 14V for UCX842A/44A

IiVizOperating Supply CurrentZener Voltage

VPIN2 = VPIN3 = 0VIi=25mA

30

0.30.31236

0.50.517

30

0.30.31236

0.50.517

mAmAmAV

X842A/3AX844A/5A

9447

98

100500

9447

98

100500

%%%

X842A/4AX843A/5AX842A/4A

157.

168.410

179.011

14.57.88.5

168.410

17.59.011.5

VVVnsVVVVVns

Notes:1.Max package power dissipation limits must be respected; low duty cycle pulse techniques are used during test maintain Tj as close

to Tamb as possible.

2.These parameters, although guaranteed, are not 100% tested in production.3.Parameter measured at trip point of latch with VPIN2 = 0.4.Gain defined as : A = ∆VPIN1/∆VPIN3; 0 ≤ VPIN3 ≤ 0.8V5.Adjust Vi above the start threshold before setting at 15 V.

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UC384XA - UC284XA

Figure 4. Open Loop Test Circuit.

VREF4.7KΩ2N2222100KΩERROR AMP.ADJUST4.7KΩCOMPVFB1KΩISENSEADJUST5KΩISENSERT/CTRTVREF123465CTD95IN343A80.1µF7Vi0.1µFOUTPUTGROUND1W1KΩViOUTPUTGROUNDHigh peak currents associated with capacitive loads necessitate careful grounding techniques. Timing andbypass capacitors should be connected close to pin 5 in a single point ground. The transistor and 5 KΩpotentiometer are used to sample the oscillator waveform and apply an adjustable ramp to pin 3.Figure 5. Oscillator Frequency vs Timing

Resistance

fo(Hz)D96IN362Figure 7. Oscillator Discharge Current vs.

Temperature.

Idischg(mA)D95IN335Vi=15VVOSC=2V1MCT=4708.51nFpF100K2.2nF8.04.7nF10K7.51K3001K3K10K30KRT(Ω)7.0-55-250255075100TA(˚C)Figure 6. Maximum Duty Cycle vs Timing

Resistor

fo(Hz)D96IN363Figure 8. Error Amp Open-Loop Gain and

Phase vs. Frequency.

(dB)80D95IN33780Gain60Vi=15VVO=2V to 4VRL=100KTA=25˚Cφ306090120150604040Phase200-20102003001K3K10K30KRT(Ω)1001K10K100K1M180f(Hz)5/16

UC384XA - UC284XA

Figure 9. Current Sense Input Threshold vs.

Error Amp Output Voltage.

Vth(V)1.0D95IN338Figure 12. Output Saturation Voltage vs. Load

Current.

Vsat(V)D95IN341Vi=15VTA=25˚CVi-1-2Source Saturation(Load to Ground)TA=25˚CTA=-40˚C0.8TA=125˚C0.60.40.20.032Vi=15V80µs Pulsed Load 120Hz RateTA=-40˚CTA=25˚CSink Saturation(Load to Vi)0200400600TA=-40˚C10GNDIO(mA)0246VO(V)Figure 10. Reference Voltage Change vs.

Source Current..

60D95IN339Figure 13. Supply Current vs. Supply Voltage.

Ii(mA)20D95IN342Vi=15V5040TA=-40˚CTA=125˚C15RT=10KCT=3.3nFVFB=0VISense=0VTA=25˚C30TA=25˚CUCX843/4520100020406010580100Iref(mA)0010UCX842/442030Vi(V)Figure 11. Reference Short Circuit Current vs.

Temperature..

ISC(mA)1009080706050-55-250255075100TA(˚C)Vi=15VRL≤0.1ΩD95IN3406/16

UC384XA - UC284XA

Figure 14. Output Waveform.

Figure 15. Output Cross Conduction

Figure 16. Oscillator and Output Waveforms.

Vi78PWMRTCLOCK4IDCT5GNDD95IN344CT5V REGOUTPUT6OUTPUTLARGE RT/SMALL CTOSCILLATORCTOUTPUTSMALL RT/LARGE CTFigure 17. Error Amp Configuration.

2.5V1mA+ZiZfD95IN345VFBCOMP21-7/16

UC384XA - UC284XA

Figure 18. Under Voltage Lockout.

7ON/OFF COMMANDTO REST OF ICViICCUC3842AUC3843AUC3844AUC3845AVONVOFF16V10V8.4V7.6V<17mA<0.5mAVOFFVOND95IN346modVCCFigure 19. Current Sense Circuit.

ERRORAMPL.ISCOMPRRSCCURRENTSENSE5GND132RR1VCURRENTSENSECOMPARATORD95IN347Peak current (is) is determined by the formula1.0V

ISmax≈------------RS

A small RC filter may be required to suppress switch transients.Figure 20. Slope Compensation Techniques.

VREGRTISRSLOPER1RSRT/CTCTISENSE8VREGRT84ISRSLOPERT/CTCTISENSE435GNDRSR135GNDD95IN3488/16

UC384XA - UC284XA

Figure 21. Isolated MOSFET Drive and Current Transformer Sensing.

VCC7Vin5.0Vref+-ISOLATIONBOUNDARYVGS Waveforms+-SR-+COMP/LATCHQ6Q1+0-50% DC+0-25% DCIpk =V(pin 1) -1.43RS(N)NSP3CD95IN349RRSNSNPFigure 22. Latched Shutdown.

4OSC8RBIASR+1mA+212N39052N39035-EA2RRD95IN350SCR must be selected for a holding current of less than 0.5mA at TA(min).The simple two transistor circuit can be used in place of the SCR as shown. All resistors are 10K.9/16

UC384XA - UC284XA

Figure 23. Error Amplifier Compensation

From VORi2RdCfRf152.5V+-EA+1mA2RRError Amp compensation circuit for stabilizing any current-mode topology exceptfor boost and flyback converters operating with continuous inductor current.+1mARPRi2CPRdCfRf15D95IN351From VO2.5V+-EA2RRError Amp compensation circuit for stabilizing current-mode boost and flybacktopologies operating with continuous inductor current.Figure 24. External Clock Synchronization.

VREF8RBIASRT4CTEXTERNALSYNC INPUT0.01µF47Ω215+-EA+ROSC2RRThe diode clamp is required if the Sync amplitude is large enough to causethe bottom side of CT to go more than 300mV below groundD95IN35210/16

UC384XA - UC284XA

Figure 25. External Duty Cycle Clamp and Multi Unit Synchronization.

VREFRA8+-5K2C5K1+-S43Q72+-EA2R4+8RBIASROSCRB655KRR5NE5551f =1.44(RA + 2RB)CDmax =RBRA + 2RBTO ADDITIONALUCX84XAsD95IN353Figure 26. Soft-Start Circuit

8RBIASR4+1mA21MΩ1C5+-EA2RROSC5Vref+-S+1V-QRD95IN311/16

UC384XA - UC284XA

Figure 27. Soft-Start and Error Amplifier Output Duty Cycle Clamp.

VCCVin78RBIASR4+1mA2R215CR1BC109VCLAMP = ·R1R1 + R2where 0 12/16

UC384XA - UC284XA

Figure 28. SO-8 Mechanical Data & Package Dimensions

mmDIM.MIN.AA1A2BCD (1)EeHhLkddd5.800.250.401.350.101.100.330.194.803.801.276.200.501.270.2280.0100.016TYP.MAX.1.750.251.650.510.255.004.00MIN.0.0530.0040.0430.0130.0070.10.150.0500.2440.0200.050TYP.MAX.0.0690.0100.0650.0200.0100.1970.157inchOUTLINE ANDMECHANICAL DATA0˚ (min.), 8˚ (max.)0.100.004Note:(1)Dimensions D does not include mold flash, protru-sions or gate burrs.Mold flash, potrusions or gate burrs shall not exceed0.15mm (.006inch) in total (both side).SO-80016023 C13/16

UC384XA - UC284XA

Figure 29. DIP-8 Mechanical Data & Package Dimensions

mmDIM.MIN.Aa1Bbb1DEee3e4FILZ3.187.952.7.627.626.65.083.811.520.1250.511.150.3560.2041.650.550.30410.929.750.3130.1000.3000.3000.2600.2000.1500.060TYP.3.320.0200.0450.0140.0080.0650.0220.0120.4300.384MAX.MIN.TYP.0.131MAX.inchOUTLINEANDMECHANICALDATADIP-814/16

UC384XA - UC284XA

Table 6. Revision History

DateMarch 1999May 2004

Revision

45

First Issue in EDOCSNOT FOR NEW DESIGN

Description of Changes

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UC384XA - UC284XA

Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequencesof use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is grantedby implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subjectto change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are notauthorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.

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