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UMW UC3842B/43B/44B/45B
PIN CONNECTION (TOP VIEW)
DESCRIPTION
The are fixed frequency current-mode PWM controller
circuits. They are specially designed for off line and DC-to-DС converter applications with a minimal number of external components. The internally implemented circuits include a trimmed oscillator for precise duty cycle control, a temperature-compensated reference, a high gain error amplifier, a current sensing comparator, and a high-current totem-pole output ideally suited for driving a power MOSFET. The protection circuitry includes built-in undervoltage lockout and current limiting.
The 3842B and 3844B have UVLO thresholds of 16V (on) and 10V (off). The corresponding thresholds for the 3843B , 3845B , are 8.4V (on) and 7.6V (off). The 3842B and 3843B can operate within 100% duty cycle. The 3844 and 3845B can operate within 50% duty cycle.
The 384XB has start-up current 0.17mA (typ.). The 384XB differs in a higher unity gain bandwidth of the error amplifier.
FEATURES
Low start-up and operating current
High-current totem pole output
Undervoltage lockout with hysteresis
Operating frequency up to 500kHz
BLOCK DIAGRAM
(T is a toggle flip-flop used only in 3844, 3845)
ABSOLUTE MAXIMUM RATINGS
CHARACTERISTIC SYMBOL VALUE UNIT
Supply voltage (low impedance source) VCC 30 V
Output current IO 1 A
Input voltage (analog inputs - pins 2, 3) VI 0.3 to 5.5 V
Error amp output sink current ISink (EA) 10 mA
Power dissipation (TA = 250C) PO 1 W
Storage temperature range TSTG -65 to 150 oC
Lead temperature (soldering 5 sec.) TL 260 oC
Operating temperature range (TJ) TJ_op -40 to +125 oC
Min ESD rating (R = 1.5k, C = 100pF) ESD 2 kV
UC3842B/3843B/3844B/3845B
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UMW UC3842B/43B/44B/45B
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ELECTRICAL CHARACTERISTICS (*VCC = 15V, RT = 10k , CT = 3.3nF, TJ = -400C to +1250C, unless otherwise specified)
CHARACTERISTICS SYMBOL TEST CONDITIONS MIN. TYP. MAX. UNIT
Reference Section
Reference output voltage VRef TJ = 25 C, IRef = 1mA 4.9 5.0 5.1 V
Line regulation VRef 12V VCC 25V 6.0 20 mV
Load regulation VRef 1mA IRef 20mA 6.0 25
Temperature stability Ts 0.4 mV/ºC
Total output variation over Line,
Load, and Temperature
VRef_tot 4.82 5.18 V
Short-circuit output current ISC -30 -75 -180 mA
Oscillator Section
Oscillation frequency f TJ = 25 C 47 52 57 kHz
Oscillation frequency f TJ = Tlow to Thigh 46 58 kHz
Frequency change with voltage f/ VCC 12V VCC 25V 0.5 1.0 %
Frequency change with temperature Ftemp TJ = Tlow to Thigh 4 %
Oscillator amplitude VOsc (peak-to-peak) 1.6 V
Error Amplifier Section
Input bias current IBias VFB = 3V -0.1 -2 A
Input voltage VI(EA) VPin1 = 2.5V 2.42 2.5 2.58 V
Open-loop voltage gain AVOL 2V V0 4V 65 90 dB
Unity gain bandwidth UGBW TJ = 25оC (Note 3) 0.5 0.6 MHz
Power supply rejection ratio PSRR 12V VCC 25 V 60 70 dB
Output sink current ISink VPin2 = 2.7V, VPin1 = 1.1V 2 7 mA
Output source current ISource VPin2 = 2.3V, VPin1 = 5V -0.5 -1.0 mA
High output voltage VOH VPin2 = 2.3V, RL = 15k to GND 5.0 7.0 V
Low output voltage VOL VPin2 = 2.7V, RL = 15k to Pin 8 0.8 1.1
Current Sense Section
Gain GV (Notes 1 and 2) 2.85 3.0 3.15 V/V
Maximum input signal VI(Max) TJ = 250C 0.9 1.0 1.1 V
TJ= Tlow to Thigh 0.85 1.1
Supply voltage rejection SVR 12V VCC 25V (Note 1) 70 dB
Input bias current IBias V Pin3 = 3V -3.0 -10 A
Output Section
Low output voltage VOL ISink = 20mA 0.08 0.4 V
ISink = 200mA 1.4 2.2
High output voltage VOH ISink = 20mA 13 13.5
ISink = 200mA 12 13.0
Output voltage with UVLO
activated
UOL(UVLO) VCC=6V, ISink=1mA 0.1 1.1 V
Rise time tR TJ = 25 C, CL = 1nF (Note 3) 45 150 ns
Fall time tF TJ = 25 C, CL = 1nF (Note 3) 35 150
Undervoltage Lockout Section
Start threshold VTH(St) 3842B/44B 14.5 16.0 17.5 V
3843B/45B 7.8 8.4 9.0
Min. operating voltage VOPR(min) 3842B/44B 8.5 10 11.5 V
(After turn-on) 3843B/45B 7.0 7.6 8.2
PWM Section
Max. duty cycle D(Max) 3842B/43B ; TJ = 25 C 94 96 100 %
3842B/43B ; TJ = Tlow to Thigh 93 100
3844B/45B ; TJ = 25 C 47 48 50
3844B/45B ; TJ = Tlow to Thigh 46 50
Min. duty cycle D(Min) 0
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Total Standby Current
Start up current IST 3843B, 3845B ; TJ = 25 C 0.13 0.3 mA
3843B, 3845B ; TJ = Tlow to Thigh 0.35
3842B, 3844B ; TJ = 25 C 0.2 0.3
3842B, 3844B ; TJ = Tlow to Thigh 0.45
Operating supply current ICC (Opr) VPin3 = VPin2 = 0V 13 17
Zener voltage VZ ICC=25 mA 30 38 V
*Adjust VCC above the start threshold before setting it to 15V.
Note 1: The parameter is measured at a trip point of a latch with VPin2=0.
Note 2: The gain is defined as A= VPin1/ VPin3; 0 VPn3 0.8V.
Note 3: These parameters, although guaranteed, are not 100% tested in production.
PIN FUNCTION
NO. FUNCTION DESCRIPTION
1 COMP This pin is the ERR AMP (Error Amplifier) output and is made for loop compensation.
2 VFB This is an inverting input of the ERR AMP. It is normally connected to the switching power supply output through a resistor
divider.
3 ISENSE A voltage proportional to an inductor current is applied to this input. The PWM uses this information to terminate the output
switch conduction.
4 RT/CT The oscillator frequency and maximum output duty cycle are programmed by connecting resistor RT to VREF and capacitor
CT to ground.
5 GND This pin is the combined control circuitry and power ground.
6 OUT This output directly drives the gate of a power MOSFET. Peak currents up to 1A are sourced and sunk by this pin.
7 VCC This pin is a positive supply of the integrated circuit.
8 VREF This is a reference output. It provides a charging current for capacitor CT through resistor RT
APPLICATION INFORMATION
Fig.1. ERR AMP configuration
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Fig.2. Undervoltage Lockout (UVLO)
Fig.3. Current sense circuit
ERR AMP
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Fig.4. Slope compensation techniques
SCR must be selected for a holding current of less than 0.5mA. A simple two-transistor circuit can be used in place of the SCR as shown
Fig.5. Latched shutdown
VREF
ERR
AMP
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Fig.6. Error amplifier compensation
Fig.7. External clock synchronization
ERR
AMP
ERR
AMP
ERR
AMP
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Fig.8. Soft-start circuit
TYPICAL PERFORMANCE CHARACTERISTICS
Fig.9. Timing resistor vs. Oscillator frequency Fig.10. Output dead-time vs. Oscillator frequency
5VREF
ERR
AMP
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Fig.11. Maximum output duty cycle vs. Timing resistor (3842/43)
Fig.12.Current sense input threshold vs. ERR AMP output voltage Fig.13. Reference short-circuit current vs. Temperature
Fig.14. Supply current vs. Supply voltage
TJ=25oC
TJ=-40oC
TJ=+125oC
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Fig.15. Oscillator and Output waveforms
VREF
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