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UC3842A/UC3843A
SMPS Controller
Features
* * * * * * * Low Start Current 0.2mA (typ) Operating Range Up To 500KHz Cycle by Cycle Current Limiting Under Voltage Lock Out With Hysteresis Short Shutdown Delay Time: typ.100ns High Current Totem-pole Output Output Swing Limiting: 22V
Description
The UC3842A/UC3843A are fixed PWM controller for OffLine and DC to DC converter applications. The internal circuits include UVLO, low start up current circuit, temperature compensated reference, high gain error amplifier, current sensing comparator, and high current totem-pole output for driving a POWER MOSFET. Also UC3842A/ UC3843A provide low start up current below 0.3mA and short shutdown delay time typ. 100ns. The UC3842A has UVLO threshold of 16V(on) and 10V(off). The UC3843A is 8.4V(on) and 7.6V(off). The UC3842A and UC3843A can operate within 100% duty cycle.
8-DIP
1
8-SOP
1
Internal Block Diagram
7 VCC 29V
VREF 8
Internal Bias 1/2VREF
5V VREF
SET/ RESET UVLO
5 GND
Good LOGIC 7 PWR
VC
VFB 2
Error Amp + -
C.S PWM Comp. LATCH 1/3 1V S R 22V 6 OUTPUT
COMP 1
5 PWR
C.S 3 RT/CT 4
T
GND
OSCILLATOR
Rev. 5.0
(c)2000 Fairchild Semiconductor International
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UC3842A/UC3843A
Absolute Maximum Ratings
Parameter Supply Voltage Output Current Analog Inputs (pin 2, 3) Error Amp. Output Sink Current Power Dissipation Symbol VCC IO VI(ANA) ISINK(EA) PD Value 30 1 - 0.3 to 6.3 10 1 Unit V A V mA W
Electrical Characteristics
(VCC = 15V, RT = 10K, CT = 3.3nF, TA = 0C to + 70C ,Unless otherwise specified) Parameter REFERENCE SECTION Output Voltage Line Regulation Load Regulation Output Short Circuit OSILLATOR SECTION Initial Accuracy Voltage Stability Amplitude Discharge Current CURRENT SENSE SECTION Gain Maximum Input Signal PSRR Input Bias Current Delay to Output GV VI(MAX) PSRR IBIAS TD (NOTE 2, 3) VPIN1 = 5V(NOTE 2) VCC = 12V to 25V (NOTE 1, 2) VPIN3 = 0 V to 2V (NOTE1) 2.85 0.9 3 1.0 70 -2 100 3.15 1.1 -10 200 V/V V dB uA ns FOSC STV VOSC IDISCHG TJ = 25C VCC = 12V to 25V VPIN4, Peak to Peak TJ = 25C, Pin4 = 2V 47 7.8 52 0.2 1.7 8.3 57 1 8.8 KHz % V mA VREF VREF VREF ISC TJ = 25C, IO = 1mA VCC = 12V to 25V IO = 1mA to 20mA Ta = 25C 4.9 5.0 6 5.1 20 V mV mV mA Symbol Conditions Min. Typ. Max. Unit
6 25 - 100 - 180
2
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UC3842A/UC3843A
Electrical Characteristics (Continued)
(VCC = 15V, RT = 10K, CT = 3.3nF, TA = 0C to + 70C, Unless otherwise specified) Parameter ERROR AMPLIFIER SECTION Input Voltage Input Bias Current Open Loop Gain Unity Gain Bandwidth PSRR Output Sink Current Output Source Current Output High Voltage Output Low Voltage OUTPUT SECTION Output Low Level Output High Level Rise Time Fall Time Output Voltage Swing Limit VOL VOH tR tF VOLIM ISINK = 20mA ISINK = 200mA ISOURCE = 20mA ISOURCE = 200mA TJ = 25C, C1 = 1nF (NOTE 1) TJ = 25C, C1 = 1nF (NOTE 1) VCC = 27V, C1 = 1nF UC3842A UC3843A UC3842A UC3843A UC3842A/UC3843A VPIN2 = VPIN3 = 0V ICC = 25mA 13 12 15 7.8 9 7.0 94 0.1 1.5 13.5 13.5 40 40 22 16 8.4 10 7.6 96 0.2 11 29 0.4 2.2 100 100 17 9.0 11 8.2 100 0 0.4 17 V V V V ns ns V V V V V % % mA mA V VI IBIAS GVO GBW PSRR ISINK ISOURCE VOH VOL TPIN1 = 2.5V VO = 2V to 4V (NOTE 1) TJ= 25C (NOTE 1) VCC = 12V to 25V (NOTE 1) VPIN2 = 2.7V VPIN1 = 1.1V VPIN2 = 2.3V VPIN1 = 5.0V VPIN2 = 2.3V R1 = 15K to GND VPIN2 = 2.7V R1 = 15K to Pin8 2.42 65 0.7 60 2 -0.5 5 2.50 -0.3 90 1 70 6 -0.8 6 0.8 2.58 -2 1.1 V uA dB MHz dB mA mA V V Symbol Conditions Min. Typ. Max. Unit
UNDER VOLTAGE LOCKOUT SECTION Start Threshold Min. Operating Voltage ( After turn on ) PWM SECTION Maximum Duty Cycle Minimum Duty Cycle TOTAL STANDBY CURRENT Start-Up Current Operating Supply Current VCC Zener Voltage IST ICC VZ DMAX DMIN VTH VTL
* Adjust VCC above the start threshold before setting at 15V Notes : 1. These parameters, although guaranteed, are not 100% tested in production. 2. Parameter measured at trip point of latch with V2 = 0V. 3. Gain defined as: GV = VPIN1VPIN3(VPIN3 = 0 to 0.8V)
3
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UC3842A/UC3843A
Mechanical Dimensions
Package
8-DIP
1.524 0.10 0.018 0.004 0.060 0.004 0.46 0.10 6.40 0.20 0.252 0.008 0.79 ) 0.031 #8 9.20 0.20 0.362 0.008 9.60 MAX 0.378 #5 2.54 0.100 5.08 MAX 0.200 7.62 0.300 3.40 0.20 0.134 0.008 3.30 0.30 0.130 0.012 0.33 0.013 MIN
#1
#4
0.25 -0.05
0~15
+0.10
0.010 -0.002
+0.004
4
(
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UC3842A/UC3843A
Mechanical Dimensions (Continued)
Package
8-SOP
MIN 1.55 0.20 0.061 0.008 0.1~0.25 0.004~0.001
#1
#8 4.92 0.20 0.194 0.008 5.13 MAX 0.202
( #4 #5 6.00 0.30 0.236 0.012
+0.10 0.15 -0.05 +0.004 0.006 -0.002
0.56 ) 0.022 1.80 MAX 0.071 MAX0.10 MAX0.004 3.95 0.20 0.156 0.008 5.72 0.225 0.50 0.20 0.020 0.008
0~
8
1.27 0.050
0.41 0.10 0.016 0.004
5
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UC3842A/UC3843A
Ordering Information
Product Number UC3842AN UC3842AD UC3843AN UC3843AD Package 8 DIP 8 SOP 8 DIP 8 SOP 0 ~ + 70C Operating Temperature
6
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UC3842A/UC3843A
7
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UC3842A/UC3843A
LIFE SUPPORT POLICY FAIRCHILD'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR INTERNATIONAL. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury of the user.
www.fairchildsemi.com 7/12/00 0.0m 001 Stock#DSxxxxxxxx " 2000 Fairchild Semiconductor International
2. A critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.

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