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UNISONIC TECHNOLOGIES CO., LTD UC3842A/3843A
CURRENT MODE PWM CONTROL CIRCUITS
SOP-8
LINEAR INTEGRATED CIRCUIT
DESCRIPTION
The UTC UC3842A/3843A provide the necessary functions to implement off-line or DC to DC fixed frequency current mode , controlled switching circuits with minimal external components.
FEATURES
*Low start up current ( Typical 0.12mA ) *Automatic feed forward compensation *Pulse-by-Pulse current limiting *Under-voltage lockout with hysteresis *Double pulse Suppression *High current totem pole output to drive MOSFET directly *Internally trimmed band gap reference *500kHz operation
DIP-8
*Pb-free plating product number: UC3842AL UC3843AL
ORDERING INFORMATION
Ordering Number Normal Lead Free Plating UC3842A-D08-T UC3842AL-D08-T UC3842A-S08-R UC3842AL-S08-R UC3842A-S08-T UC3842AL-S08-T UC3843A-D08-T UC3843AL-D08-T UC3843A-S08-R UC3843AL-S08-R UC3843A-S08-T UC3843AL-S08-T Package DIP-8 SOP-8 SOP-8 DIP-8 SOP-8 SOP-8 Packing Tube Tape Reel Tube Tube Tape Reel Tube
UC3842AL-D08-T (1)Packing Type (2)Package Type (3)Lead Plating (1) T: Tube, R: Tape Reel (2) D08: DIP-8, S08: SOP-8 (3) L: Lead Free Plating, Blank: Pb/Sn
www.unisonic.com.tw Copyright (c) 2005 Unisonic Technologies Co., Ltd
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UC3842A/3843A
PIN CONFIGURATION
COMP 1
LINEAR INTEGRATED CIRCUIT
8
VREF
VFB
2
7
VCC
Current Sense
3
6
Output
RT/CT
4
5
GND
BLOCK DIAGRAM
7 Vcc
VREF
8 Internal Bias 1/2VREF
5V REF
S/R 5 GND U.V.L.O CURRENT SENSE COMPARATOR R PWM LATCH S
VREF Good Logic 1/3VREF
7
Vcc
VFB COMP CURRENT SENSE
2 1 3 ERROR AMPLIFIER 1V
6
OUTPUT
5 RT/CT 4 OSCILLATOR
GND
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UC3842A/3843A
ABSOLUTE MAXIMUM RATINGS (Ta=25 )
PARAMETER Supply Voltage(Low Impedance Source) Supply Voltage(ICC<30mA) Output Current ( Peak ) Output Energy (capacity Load) Analog Inputs(pin 2,3) Error Amplifier Output Sink Current SYMBOL VCC VCC IO(PEAK)
LINEAR INTEGRATED CIRCUIT
UNIT V V A 5 J VI(ANA) -0.3 ~ +6.3 V ISINK(EA) 10 mA DIP-8 1.0 W Power Dissipation( Ta 25C) PD 0.5 W SOP-8 Derated at Ta>25C PD 8 mW/C Junction Temperature TJ +150 C Storage Temperature TSTG -65 ~ +150 C Note Absolute maximum ratings are those values beyond which the device which the device could be permanently damaged. Absolute maximum ratings are stress ratings only and functional device operation is not implied.
RATINGS 30 Self Limiting 1
ELECTRICAL CHARACTERISTICS
(0C T 70C, VCC=15V, RT=10k, CT=3.3nF, unless otherwise specified) SYMBOL VREF VREF VREF TEST CONDITIONS TJ=25C,IOUT=1mA 12 VIN25V 1 IOUT=20mA (Note 1) Line, Load, Temp(Note 1) 10Hz f 10kHz,TJ=25C (Note 1) Ta=25C,1000Hrs(Note 1) MIN 4.9 TYP 5 6 6 0.2 50 5 -100 52 0.2 5 1.7 2.50 -0.3 90 1 70 6 -0.8 6 0.7 MAX 5.1 20 25 0.4 5.18 25 -180 57 1 UNIT V mV mV mV/C V V mV mA kHz % % V V A dB MHz dB mA mA V V PARAMETER Reference Section Output Voltage Line Regulation Load Regulation Temperature Stability Total Output Variation Output Noise Voltage Long Term Stability Output Short Circuit Oscillator Section Initial Accuracy Voltage Stability Temperature Stability Amplitude Error Amplifier Section Input Voltage Input Bias Current AVOL Unity Gain Bandwidth PSRR Output Sink Current Output Source Current VOUT High VOUT Low
4.82
Vosc ISC
-30 47
f TJ=25C f/Vcc 12 VCC 25V Tmin Ta Tmax(Note 1) Vosc Vpin 4 peak to peak VI(EA) II(BIAS) Vpin 1=2.5V 2 VOUT 4V TJ=25C (Note 1) I2 VCC 25V Vpin 2=2.7V,Vpin 1=1.1V Vpin 2=2.3V,Vpin 1=5V Vpin 2=2.3V, RL=15k to GND Vpin 2=2.7V,Vpin 1=1.1V
2.42 60 0.7 60 2 -0.5 5
2.58 -2
IO(SINK) IO(SOURCE) VOH VOL
1.1
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ELECTRICAL CHARACTERISTICS(Cont.)
PARAMETER Current Sense section Gain Maximum Input signal PSRR Input Bias Current Delay to Output Output Section Low Output Level High VOH SYMBOL GV VI(MAX) IBIAS Vpin 3=0 to 2V IO(SINK)=20mA IO(SINK)=200mA IO(SOURCE)=20mA IO(SOURCE)=200mA TJ=25C,CL=1nF(Note 1) TJ=25C,CL=1nF(Note 1)
LINEAR INTEGRATED CIRCUIT
TEST CONDITIONS (Note 2,3) Vpin 1=5V( Note 2) 12 VCC 25V
MIN 2.85 0.9
TYP 3 1 70 -2 150 0.1 1.5 13.5 13.5 50 50 16 8.4 10 7.6 97
MAX 3.15 1.1 -10 300 0.4 2.2
UNIT V/V V dB A ns V V V V ns ns V V V V % % mA mA V
VOL
13 12
Rise Time tR Fall Time tF Under-Voltage Lockout Output Section 3842A Start Threshold VTH(ST) 3843A 3842A Min. Operating Voltage VOPR(MIN) After Turn On 3843A PWM Section MAX D(MAX) Duty Cycle Min D(MIN) Total Standby Current Start-up Current IST Operating Supply Current ICC(OPR) Vpin 2=Vpin 3=0V VCC Zener Voltage Vz ICC=25mA Note:1.These parameters, although guaranteed ,are not 100% tested in production. 2. Parameters measured at trip point of latch with Vpin 2=0. 3. Gain defined as:
A= Vpin 1 Vpin 3 ; 0 Vpin3 0.8V
150 150 17.5 9 11.5 8.2 100 0 0.3 17
14.5 7.8 8.5 7 95
0.12 11 34
4. Adjust VCC above the start threshold before setting at 15V.
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UC3842A/3843A
OPEN-LOOP LABORATORY TEST FIXTURE
LINEAR INTEGRATED CIRCUIT
VREF
4.7k
RT
100k 0.1 F
1 2 3
8 7 6 5
A
0.1 F
Vcc
Error Amp Adjust
4.7k Isense Adjust
1k / 1W OUTPUT
5k 4 CT
High peak current associated with capacity loads necessitate careful grounding techniques. Timing and bypass capacitors should be connected close to pin 5 in single point GND. The transistor and 5k potentio-meter are used to sample the oscillator waveform and apply an adjustable Ramp to Pin 3.
UNDER-VOLTAGE LOCKOUT
Icc Vcc
<15mA
7
ON/OFF Command to rest of IC
Von=16V Voff=10V
<1mA Voff Von
Vcc
During Under-Voltage Lockout, the output driver is biased to a high impedance state. Pin 6 should be shunt to GND with a bleeder resistor to prevent activating the power switch with output leakage currents.
ERROR AMPLIFIER CONFIGURATION
2.5V
0.5mA
Zi Zf
2 1
Error amplifier can source or sink up to 0.5mA
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UC3842A/3843A
CURRENT SENSE CIRCUIT
Error Amplifier 2R Is R 1 R Rs C 5 3 1V
LINEAR INTEGRATED CIRCUIT
Current Sense Comparator
Peak current (Is) determined by the formula: Ismax=10V/Rs. A small RC filter be required to suppress switch transients.
SLOPE COMPENSATION
8 4
CT R1
0.1 F
RT
3
R2 C
Isense Rsense
A fraction of the oscillator ramp can be resistively summed with the current sense signal to provide slope compensation for converts requiring duty cycles over 50%.Note that capacitor C, forms a filter with R2 to suppress the leading edge switch spikes.
OSCILLATOR SECTION
Large RT Small CT RT 4 5 CT Small RT Large CT V4 INTERNAL CLOCK V4 INTERNAL CLOCK
8
Dead time vs. CT(RT>5k)
Timing Resistance vs. Frequency
100
100 CT=2.2nF
10
RT (k ) s)
10
1
CT=4.7nF CT=10nF CT=22nF CT=47nF CT=100nF 10 2 10 3 10 4 105 Frequency (Hz) 10 6
td (
0.1
1 1 10 CT (nF) 100
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UC3842A/3843A
SHUTDOWN TECHNIQUES
LINEAR INTEGRATED CIRCUIT
1k
8
1
330
Shutdown
3
500 To current Sense resistor
Shutdown
Shutdown UTC UC3842A can be accomplished by two methods; either raise pin 3 above 1V or pull Pin 1 below a voltage two diode drops above ground. Either method caused the output of PWM comparator to be high(refer to block diagram).The PWM latch is reset dominant so that the output will remain low until the next clock cycle after the shutdown condition at pins 1 and/or 3 is removed . In one example, an externally latched shut -down may be accomplished by adding an SCR which be reset by cycling VCC below the lower UVLO threshold. At this point the reference turns off allowing the SCR to reset.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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UC3842A/3843A
TYPICAL CHARACTERISTICS
Output Saturation Characteristics
LINEAR INTEGRATED CIRCUIT
Error Amplifier Open-Loop Frequency Response
4
100
Saturation Voltage (V)
60 40 20 0
-45 -90 -135 -180
2
1
0
0.01
0.1 1 Output Current (Sourse or Sink Current) (A)
10 102 10 3 10 4 10 5 10 6 10 7 Frequency (Hz)
VREF Temperature Drift 5.02 5.01
VREF (V)
Istart Temperature Drift 550
Vcc=15V IOUT=1mA
Istart (mA)
500 Vcc=9V 450 400 350 300 250 -50 -25 0 25 50 75 100 125 150 Temperature ( )
5.00 4.99 4.98 4.97 4.96 -50 -25 0 25 50 75 100 125 150 Temperature ( )
Icc Temperature Drift 15 14 Vcc=15V IOUT=1mA
Icc (mA)
13 12 11 10 9 -50 -25 0 25 50 75 100 125 150 Temperature ( )
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PHASE (Degree)
3
Voltage Gain (dB)
Vcc=15V Ta=+25 Ta=-40
80
0
UC3842A/3843A
LINEAR INTEGRATED CIRCUIT
UTC assumes no responsibility for equipment failures that result from using products at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other parameters) listed in products specifications of any and all UTC products described or contained herein. UTC products are not designed for use in life support appliances, devices or systems where malfunction of these products can be reasonably expected to result in personal injury. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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