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(R)
UC2842A/3A/4A/5A UC3842A/3A/4A/5A
HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
.TRI .CURRENTMODEOPERATI .AUTOMATI .LATCHI .I .HI .UNDERVOLTAGELOCKOUTWI .LOWSTART.DOUBLEPULSESUPPRESSI
DESCRIPTION
MMED OSCILLATOR DISCHARGE CURRENT ON TO 500kHz C FEED FORWARD COMPENSATION NG PWM FOR CYCLE-BY-CYCLE CURRENT LIMITING NTERNALLY TRIMMED REFERENCE WITH UNDERVOLTAGE LOCKOUT GH CURRENT TOTEM POLE OUTPUT TH HYSTERESIS UP CURRENT (< 0.5mA) ON
Minidip
SO8
TheUC384xA family ofcontrolICs providesthe necessary features to implement off-line or DC to DC fixed frequency current mode control schemes with a minimal external parts count. Internally implemented circuits include a trimmed oscillator for precise DUTY CYCLE CONTROL under voltage lockoutfeaturingstart-up current less than0.5mA,a precision reference trimmed for accuracy at the error amp input, logicto insure latched operation,a PWM
comparatorwhich alsoprovidescurrent limit control, and a totem pole output stage designed to source or sink high peakcurrent. The outputstage, suitable for driving N-Channel MOSFETs, is low in the offstate. Differences between members of this family are the under-voltagelockout thresholds and maximum duty cycle ranges. The UC3842A and UC3844A have UVLO thresholds of 16V (on) and 10V (off), ideally suitedoff-lineapplicationsThecorrespondingthresholds for the UC3843A and UC3845A are 8.5 V and 7.9V. The UC3842A and UC3843A can operate to dutycycles approaching100%.A range of the zeroto < 50 % is obtainedby theUC3844Aand UC3845Aby the addition of an internal toggle flip flopwhich blanks the output off every otherclock cycle.
BLOCK DIAGRAM (toggle flip flop used only in UC3844A and UC3845A)
Vi 7 34V GROUND 5 UVLO S/R 5V REF INTERNAL BIAS VREF GOOD LOGIC RT/CT 4 OSC ERROR AMP. 2R R 1V T
8
VREF 5V 50mA
2.50V
6
OUTPUT
VFB COMP CURRENT SENSE
2 1 3
+ -
S R CURRENT SENSE COMPARATOR PWM LATCH
UC3842A
D95IN331
March 1999
1/15
UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
ABSOLUTE MAXIMUM RATINGS
Symbol Vi Vi IO EO Parameter Supply Voltage (low impedance source) Supply Voltage (Ii < 30mA) Output Current Output Energy (capacitive load) Analog Inputs (pins 2, 3) Error Amplifier Output Sink Current Ptot Ptot Tstg TJ TL Power Dissipation at Tamb 25 C (Minidip) Power Dissipation at Tamb 25 C (SO8) Storage Temperature Range Junction Operating Temperature Lead Temperature (soldering 10s) Valu e 30 Self Limiting 1 5 - 0.3 to 5.5 10 1.25 800 - 65 to 150 - 40 to 150 300 A J V mA W mW C C C Un it V
* All voltages are with respect to pin 5, all currents are positive into the specified terminal.
PIN CONNECTION (top view) Minidip/SO8
COMP VFB ISENSE RT/CT
1 2 3 4
D95IN332
8 7 6 5
VREF Vi OUTPUT GROUND
PIN FUNCTIONS
No 1 2 3 4 5 6 7 8 Function COMP VFB ISENSE RT/CT GROUND OUTPUT VCC Vref Description 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.
ORDERING NUMBERS
SO8 UC2842AD1; UC2843AD1; UC2844AD1; UC2845AD1; UC3842AD1 UC3843AD1 UC3844AD1 UC3845AD1 Minidip UC2842AN; UC2843AN; UC2844AN; UC2845AN; UC3842AN UC3843AN UC3844AN UC3845AN
2/15
UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
THERMAL DATA
Symbo l Rth j-amb Description Thermal Resistance Junction-ambient. max. Minid ip 100 SO 8 150 Unit C/W
ELECTRICAL CHARACTERISTICS ( [note 1] Unless otherwise stated, these specifications apply for -25 < Tamb < 85C for UC284XA; 0 < Tamb < 70C for UC384XA; Vi = 15V (note 5); RT = 10K; CT = 3.3nF)
Symbo l Parameter T est Cond it ion s UC284XA UC384XA Min. T yp. Max. Min. Typ . Max. 4.95 5.00 5.05 4.90 5.00 5.10 2 3 0.2 4.9 50 5 -30 Tj = 25C TA = Tlow to Thigh (peak to peak) 47 - - - 7.8 25 -30 47 - - - 7.8 5.1 4.82 50 5 25 20 25 2 3 0.2 5.18 20 25 Uni t
REFERENCE SECTION VREF V REF V REF Output Voltage Line Regulation Load Regulation Tj = 25C Io = 1mA 12V Vi 25V 1 Io 20mA (Note 2) Line, Load, Temperature 10Hz f 10KHz Tj = 25C (note 2) Tamb = (note 2) 125C, 1000Hrs V mV mV mV/C V V mV mA KHz % % V mA V A dB MHz dB mA mA V 1.1 V
VREF/T Temperature Stability Total Output Variation eN Output Noise Voltage Long Term Stability ISC Output Short Circuit
-100 -180 52 0.2 5 1.6 8.3 57 1 - - 8.8
-100 -180 52 0.2 5 1.6 8.3 57 1 - - 8.8
OSCILLATOR SECTION fOSC Frequency fOSC/V fOSC/T VOSC Idischg V2 Ib BW PSRR Io Io Frequency Change with Temp. Oscillator Voltage Swing
Frequency Change with Volt. VCC = 12V to 25V
Discharge Current (VOSC =2V) TJ = 25C Input Voltage Input Bias Current AVOL Unity Gain Bandwidth Power Supply Rejec. Ratio Output Sink Current Output Source Current VOUT High VOUT Low VPIN1 = 2.5V VFB = 5V 2V Vo 4V TJ = 25C 12V Vi 25V VPIN2 = 2.7V VPIN1 = 1.1V VPIN2 = 2.3V VPIN1 = 5V VPIN2 = 2.3V; R L = 15K to Ground VPIN2 = 2.7V; R L = 15K to Pin 8 (note 3 & 4) VPIN1 = 5V (note 3) 12 Vi 25V (note 3)
ERROR AMP SECTION 2.45 2.50 2.55 2.42 2.50 2.58 -0.1 65 0.7 60 2 -0.5 5 90 1 70 12 -1 6.2 0.8 1.1 -1 65 0.7 60 2 -0.5 5 -0.1 90 1 70 12 -1 6.2 0.8 -2
CURRENT SENSE SECTION GV Gain V3 SVR Ib Maximum Input Signal Supply Voltage Rejection Input Bias Current Delay to Output
2.85 0.9
3 1 70 -2 150
3.15 2.85 1.1 -10 300 0.9
3 1 70 -2 150
3.15 1.1 -10 300
V/V V dB A ns
3/15
UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
ELECTRICAL CHARACTERISTICS (continued)
Symbo l OUTPUT SECTION VOL VOH VOLS tr tf Output Low Level ISINK = 20mA ISINK = 200mA Output High Level ISOURCE = 20mA ISOURCE = 200mA UVLO Saturation Rise Time Fall Time Start Threshold VCC = 6V; ISINK = 1mA Tj = 25C CL = 1nF (2) Tj = 25C CL = 1nF (2) X842A/4A X843A/5A Min Operating Voltage After Turn-on PWM SECTION Maximum Duty Cycle X842A/3A X844A/5A Minimum Duty Cycle TOTAL STANDBY CURRENT Ist Ii V iz Start-up Current Vi = 6.5V for UCX843A/45A Vi = 14V for UCX842A/44A Operating Supply Current Zener Voltage VPIN2 = VPIN3 = 0V Ii = 25mA 30 0.3 0.3 12 36 0.5 0.5 17 30 0.3 0.3 12 36 0.5 0.5 17 mA mA mA V 94 47 96 48 100 50 0 94 47 96 48 100 50 0 % % % X842A/4A X843A/5A 15 7.8 9 7.0 13 12 0.1 1.6 13.5 13.5 0.7 50 50 16 8.4 10 7.6 1.2 150 150 17 9.0 11 8.2 14.5 7.8 8.5 7.0 0.4 2.2 13 12 0.1 1.6 13.5 13.5 0.7 50 50 16 8.4 10 7.6 1.2 150 150 17.5 9.0 11.5 8.2 0.4 2.2 V V V V V ns ns V V V V Parameter T est Cond itions UC284XA UC384XA Min . Typ . Max. Min. T yp. Max. Un it
UNDER-VOLTAGE LOCKOUT SECTION
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 V PIN2 = 0. 4. Gain defined as : VPIN1 A= ; 0 VPIN3 0.8 V VPIN3 5. Adjust Vi above the start threshold before setting at 15 V.
4/15
UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
Figure 1: Open Loop Test Circuit.
VREF 4.7K 2N2222 100K ERROR AMP. ADJUST 4.7K COMP VFB 1K ISENSE ADJUST 5K ISENSE RT/CT RT VREF 1 2 8 7 Vi 0.1F OUTPUT GROUND 1W 1K OUTPUT A 0.1F Vi
UC3842A
3 4 6 5
CT
D95IN343
GROUND
High peak currents associatedwith capacitive loads necessitate careful grounding techniques. Timing and bypass capacitors should be connected close
to pin 5 in a single point ground. The transistor and 5 K potentiometerareusedto samplethe oscillator waveform and apply an adjustable ramp to pin 3.
Figure 2: Oscillator Frequency vs Timing Resistance
fo (Hz)
D96IN362
Figure 3: Maximum Duty Cycle vs Timing Resistor
fo (Hz)
D96IN363
80 1M
CT =4 70 pF
1nF
60
100K
2.2
nF
4.7
nF
40
10K 20
1K 300 1K 3K 10K 30K RT()
0 300 1K 3K 10K 30K RT()
5/15
UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
Figure 4: Oscillator Discharge Current vs. Temperature.
I dischg (mA)
D95IN335
Figure 5: Error Amp Open-Loop Gain and Phase vs. Frequency.
(dB) 80
D95IN337
30 60 90
Vi=15V VOSC=2V
8.5
Gain
60
Vi=15V VO=2V to 4V RL=100K TA=25C
8.0
40
Phase
20 120 150 180 f(Hz)
7.5 0 7.0 -55 -25 0 25 50 75 100 TA(C) -20 10
100
1K
10K
100K
1M
Figure 6: Current Sense Input Threshold vs. Error Amp Output Voltage.
Vth (V) 1.0
D95IN338
Figure 7: Reference Voltage Change vs. Source Current.
60
D95IN339
Vi=15V
50
Vi=15V
TA=25C
0.8
40
TA=-40C TA=125C
TA=125C
0.6 0.4
30 20
TA=-40C
0.2 0.0
10 0
0
2
4
6
VO(V)
0
20
40
60
TA=25C
80
100 Iref(mA)
Figure 8: Reference Short Circuit Current vs. Temperature.
ISC (mA) 100 90 80 70 60 50 -55 -25 0 25 50 75 100 TA(C) Vi=15V RL0.1
D95IN340
6/15
UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
Figure 9: Output Saturation Voltage vs. Load Current.
Vsat (V)
D95IN341
Figure 10: Supply Current vs. Supply Voltage.
Ii (mA) 20
D95IN342
Vi
-1 -2
Source Saturation (Load to Ground) TA=25C TA=-40C
Vi=15V 80s Pulsed Load 120Hz Rate
15
R T=10K C T=3.3nF V FB=0V I Sense=0V T A=25C
UCX843/45
10
2 1 0 0
TA=-40C TA=25C
5
Sink Saturation (Load to Vi)
200 400 600
GND
0
IO(mA)
0
10
UCX842/44
3
20
30
Vi(V)
Figure 11: Output Waveform.
Figure 12: Output Cross Conduction
Vi =30V CL = 15pF TA = 25C VO 20V/DIV
90%
Vi =15V CL = 1.0nF TA = 25C
ICC 10% 50ns/DIV 100ns/DIV 100mA/DIV
Figure 13: Oscillator and Output Waveforms.
Vi 7 8 5V REG PWM RT CLOCK 4 OSCILLATOR ID CT 5 GND
D95IN344
CT
OUTPUT 6 OUTPUT LARGE RT/SMALL CT
CT
OUTPUT SMALL RT/LARGE CT
7/15
UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
Figure 14 : Error Amp Configuration.
2.5V
1mA + VFB COMP Zf
D95IN345
Zi
2 1
-
Figure 15 : Under Voltage Lockout.
Vi
7
ON/OFF COMMAND TO REST OF IC
ICC
UC3842A UC3843A UC3844A UC3845A VON VOFF 16V 10V 8.4V 7.6V
<17mA
<0.5mA VOFF VON
VCC
Fig.15-UC3842A
Figure 16 : Current Sense Circuit .
ERROR AMPL. IS COMP R RS C CURRENT SENSE 5 GND 1
2R R 1V
3
CURRENT SENSE COMPARATOR
D95IN347
Peak current (is) is determined by the formula 1.0 V IS max RS A small RC filter may be required to suppress switch transients.
8/15
UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
Figure 17 : Slope Compensation Techniques.
VREG RT IS RSLOPE R1 RS RT/CT CT ISENSE
8
VREG RT
8
4
UC3842A
IS RSLOPE
RT/CT CT ISENSE
4
UC3842A
3 5 GND RS
R1
3 5 GND
D95IN348
Figure 18 : Isolated MOSFET Drive and Current Transformer Sensing.
VCC Vin
7
5.0Vref
+ -
ISOLATION BOUNDARY VGS Waveforms
+ S R + COMP/LATCH
6
Q1
+ 0 -
50% DC
+ 0 -
25% DC
Q
Ipk =
V(pin 1) -1.4 3RS
(N ) N
S P
3 C
D95IN349
R RS NS NP
9/15
UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
Figure 19 : Latched Shutdown.
4
OSC
8 R BIAS R + 1mA + 2 EA 2R
R
1 5
2N 3905 2N 3903
D95IN350
SCR 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.
Figure 20: Error Amplifier Compensation
From VO Ri 2 Rd Cf Rf 1
2.5V
+ 1mA + EA 2R
R
5
Error Amp compensation circuit for stabilizing any current-mode topology except for boost and flyback converters operating with continuous inductor current.
+ 1mA RP Ri 2 CP Rd Cf Rf 1 5
D95IN351
From VO
2.5V
+ EA
2R
R
Error Amp compensation circuit for stabilizing current-mode boost and flyback topologies operating with continuous inductor current.
10/15
UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
Figure 21: External Clock Synchronization.
V REF 8 R BIAS RT 4 CT EXTERNAL SYNC INPUT 0.01F 2 1 + EA + R
OSC
2R
47
R
5
The diode clamp is required if the Sync amplitude is large enough to cause the bottom side of CT to go more than 300mV below ground
D95IN352
Figure 22: External Duty Cycle Clamp and Multi Unit Synchronization.
VREF RA 8 4
8 R BIAS R 3 4 + Q + 5K 1 7 + EA 2R
RB 6 5
5K
+ 5K
R
OSC
2 C
S
2
R
NE555
1 5 TO ADDITIONAL UCX84XAs UCX84XAs
D95IN353
f=
1.44 (RA + 2RB)C
Dmax =
RB RA + 2RB
11/15
UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
Figure 23: Soft-Start Circuit
8 R BIAS R 4 + 1mA 2 1M 1 C 5 + EA 2R
5Vref + -
OSC
S Q + R 1V R
D95IN354
Figure 24: Soft-Start and Error Amplifier Output Duty Cycle Clamp.
VCC
Vin
7 + S + R 1V Comp/Latch 5 C R1 BC109 VCLAMP = RS R Q 5 VCLAMP RS R BIAS R 4 + 1mA 2 R2 + EA 2R 6 + 7 OSC Q1 VClamp 1
D95IN355
8
5Vref
*
R1 R1 + R2
where 0 Ipk(max) =
12/15
UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
mm MIN. A a1 a2 a3 b b1 C c1 D (1) E e e3 F (1) L M S 3.8 0.4 4.8 5.8 1.27 3.81 4.0 1.27 0.6 8 (max.) 0.15 0.016 0.65 0.35 0.19 0.25 0.1 TYP. MAX. 1.75 0.25 1.65 0.85 0.48 0.25 0.5 0.026 0.014 0.007 0.010 0.004 MIN. inch TYP. MAX. 0.069 0.010 0.065 0.033 0.019 0.010 0.020
DIM.
OUTLINE AND MECHANICAL DATA
45 (typ.) 5.0 6.2 0.189 0.228 0.050 0.150 0.157 0.050 0.024 0.197 0.244
SO8
(1) D and F do not include mold flash or protrusions. Mold flash or potrusions shall not exceed 0.15mm (.006inch).
13/15
UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
DIM. MIN. A a1 B b b1 D E e e3 e4 F I L Z 3.18 7.95 0.51 1.15 0.356 0.204
mm TYP. 3.32 0.020 1.65 0.55 0.304 10.92 9.75 2.54 7.62 7.62 6.6 5.08 3.81 1.52 0.125 0.313 0.045 0.014 0.008 MAX. MIN.
inch TYP. 0.131 MAX.
OUTLINE AND MECHANICAL DATA
0.065 0.022 0.012 0.430 0.384 0.100 0.300 0.300 0.260 0.200 0.150 0.060
Minidip
14/15
UC2842A/3A/4A/5A - UC3842A/3A/4A/5A
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of 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 granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics (c) 1999 STMicroelectronics - Printed in Italy - All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - France - Germany - Italy - Japan - Korea - Malaysia - Malta - Mexico - Morocco - The Netherlands Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdom - U.S.A. http://www.st.com
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