Datasheet

UNISONIC TECHNOLOGIES CO., LTD
UC3842B/3843B
LINEAR INTEGRATED CIRCUIT
HIGH PERFORMANCE
CURRENT MODE
CONTROLLERS

DESCRIPTION
The UTC UC3842B/3843B are specifically designed for
off-line and dc-to-dc converter applications offering the designer
a cost-effective solution with minimal external components.
The UC3842B has UVLO thresholds 16V (on) and 10V(off),
ideally suited for off-line converters. The UC3843B is tailored for
lower voltage applications having UVLO thresholds of 8.4V(on)
and 7.6V(off).

FEATURES
* Trimmed oscillator for precise frequency control
* Oscillator frequency guaranteed at 250kHz
* 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 startup and operating current

ORDERING INFORMATION
Ordering Number
Lead Free
Halogen Free
UC3842BL-D08-T
UC3842BP-D08-T
UC3842BP-S08-R
UC3843BL-D08-T
UC3843BP-D08-T
UC3843BP-S08-R
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Copyright © 2015 Unisonic Technologies Co., Ltd
Package
Packing
DIP-8
SOP-8
DIP-8
SOP-8
Tube
Tape Reel
Tube
Tape Reel
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QW-R103-012.F
UC3842B/3843B

LINEAR INTEGRATED CIRCUIT
MARKING
Package
UC3842B
UC3843B
8
7
6
5
UTC
UC3843B
DIP-8
1
2
3
4
Date Code
L: Lead Free
P: Halogen Free
Lot Code
SOP-8


PIN CONFIGURATION
COMP
1
8
VREF
VFB
2
7
VCC
CS
3
6
OUTPUT
RTCT
4
5
GND
PIN DESCRIPTIONS
PIN NO.
1
PIN NAME
COMP
I/O
O
2
VFB
I
3
4
5
6
7
8
CS
RTCT
GND
OUTPUT
VCC
VREF
I
I
O
O
DESCRIPTION
Error amp output to provide loop compensation maintaing VFB at 2.5V
Error amp inverting input, The non-inverting input of error amp is 2.5V band
gap reference
Current sense input to PWM control gate drive of output
To set oscillator frequency and maximum output duty cycle
Power ground
To direct drive power MOSFET
Power supply
5V regulated output provides charging current for CT through RT
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QW-R103-012.F
UC3842B/3843B

LINEAR INTEGRATED CIRCUIT
BLOCK DIAGRAM
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
LINEAR INTEGRATED CIRCUIT
ABSOLUTE MAXIMUM RATINGS(TA=25°C, unless otherwise specified)
PARAMETER
SYMBOL
RATINGS
UNIT
Total Power Supply and Zener Current
(ICC + IZ)
30
mA
Output Current, Source or Sink (Note 2)
IO
1.0
A
Output Energy (capacitive load per cycle)
W
5.0
μJ
Current Sense and Voltage Feedback Inputs
VIN
-0.3 ~ +5.5
V
Error Amp. Output Sink Current
IO(SINK)
10
mA
DIP-8
1250
mW
Power Dissipation
PD
SOP-8
800
mW
Operating Junction Temperature
TJ
+150
°C
Operating Temperature
TOPR
0 ~ +70
°C
Storage Temperature
TSTG
-65 ~ +150
°C
Notes: 1. Absolute maximum ratings are those values beyond which the device could be permanently damaged.
Absolute maximum ratings are stress ratings only and functional device operation is not implied.
2. Maximum Package power dissipation limits must be observed.

THERMAL DATA
PARAMETER
Junction to Ambient

SYMBOL
DIP-8
SOP-8
θJA
RATINGS
100
156
UNIT
C/W
C/W
ELECTRICAL CHARACTERISTICS
(0°C ≤TA≤70°C, VCC=15V (Note 1), RT=10k, CT=3.3nF, unless otherwise specified)
PARAMETER
SYMBOL
TEST CONDITIONS
REFERENCE SECTION
Output Voltage
VREF
IO=1.0mA, TJ =25°C
Line Regulation
∆VLINE
VCC=12V ~ 25V
Load Regulation
∆VLOAD
IO=1.0mA ~ 20mA
Temperature Stability
TS
Total Output Variation
VREF
Line, Load, Temperature
Output Noise Voltage
eN
F=10kHz ~ 10Hz, TJ =25°C
Long Term Stability
S
TA=125°C,1000Hrs
Output Short Circuit Current
ISC
OSCILLATOR SECTION
TJ =25°C
Frequency
F
TA=0°C ~ 70°C
TJ =25°C (RT=6.2k,CT=1.0nF)
Frequency Change with Voltage
fOSC/V 12 ≤ VCC ≤25V
Frequency Change with
fOSC/T 0°C ≤TA ≤70°C
Temperature
Oscillator Voltage Swing
VOSC
(Peak to Peak)
TJ =25°C
Discharge Current
IDISCHG
0°C ≤TA ≤70°C
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MIN
TYP
MAX
UNIT
4.9
5.0
2.0
3.0
0.2
5.1
20
25
V
mV
mV
mV/°C
V
μV
mV
mA
4.82
-30
49
48
225
7.8
7.6
5.18
50
5
-85
52
250
0.2
-180
55
56
275
1.0
kHz
%
0.5
%
1.6
V
8.3
8.3
8.8
8.8
mA
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LINEAR INTEGRATED CIRCUIT
ELECTRICAL CHARACTERISTICS (Cont.)
PARAMETER
ERROR AMPLIFIER SECTION
Voltage Feedback Input
Input Bias Current
Open Loop Voltage Gain
Unity Gain Bandwidth
Power Supply Rejection Ratio
Output Sink Current
Output Source Current
Output Voltage Swing High State
Output Voltage Swing Low State
CURRENT SENSE SECTION
Current Sense Input Voltage Gain
Maximum Current Sense Input
Threshold
Power Supply Rejection Ratio
Input Bias Current
Propagation Delay
OUTPUT SECTION
SYMBOL
MIN
TYP
MAX
UNIT
Vo=2.5V
VFB=5.0V
2 ≤VO≤4V
TJ =25°C
I2V≤VCC≤25V
VO=1.1V,VFB =2.7V
VO=5.0V,VFB=2.3V
VFB=2.3V, RL=15k to GND
VFB=2.7V, RL=15k to VREF
2.42
2.50
-0.1
90
1.0
70
12
-1.0
6.2
0.8
2.58
-2.0
1.1
V
μA
dB
MHz
dB
mA
mA
V
V
(Note 2, 3)
2.85
3.0
3.15
V/V
VI(THR)
(Note 2)
0.9
1.0
1.1
V
PSRR
II(BIAS)
12≤Vcc≤25V (Note 2)
Current Sense Input to Output
70
-2
150
-10
300
dB
μA
ns
ISINK=20mA
ISINK=200mA
ISOURCE=20mA
ISOURCE=200mA
0.1
1.6
13.5
13.4
0.4
2.2
V
V
V
V
VCC=6.0V,ISINK=1.0mA
0.1
1.1
V
TJ =25°C, CL=1nF
TJ =25°C, CL=1nF
50
50
150
150
ns
ns
14.5
7.8
8.5
7.0
16
8.4
10
7.6
17.5
9
11.5
8.2
V
V
V
V
94
96
0
%
%
0.3
0.5
mA
12
36
17
mA
V
VFB
II(BIAS)
GVO
GBW
PSRR
ISINK
ISOURCE
VOH
VOL
GV
tD(IN/OUT)
Output Low Voltage
VOL
Output High Voltage
VOH
Output Voltage with UVLO
VOL (UVLO)
Activated
Output Voltage Rise Time
tR
Output Voltage Fall Time
tF
UNDER-VOLTAGE LOCKOUT SECTION
Startup Threshold
Min. Operating Voltage After
Turn-on(VCC)
PWM SECTION
MAX
Duty Cycle
MIN
Total DEVICE
VTHR
VCC(MIN)
TEST CONDITIONS
UC3842B
UC3843B
UC3842B
UC3843B
DC
VCC=6.5V for UC3843B
VCC=14V for UC3842B
Power Operating Supply Current
ICC+IC
Note 1
Power Supply Zener Voltage
VZ
ICC=25mA
Note: 1. Adject VCC above the Startup threshold before setting to 15V.
2. This parameter is measured at the latch trip point with VFB=0V.
V Output Compensation
3. Comparator gain is defined as : GV
V Current Sense Input
Power Startup Supply Current
13
12
ICC+IC
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65
0.7
60
2.0
-0.5
5.0
30
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LINEAR INTEGRATED CIRCUIT
TYPICAL APPLICATION CIRCUIT
Open Loop Test Circuit
All of the parameters are not all tested in production, although been guaranteed. The timing and bypass capacitors
must be connected to Pin 5 in a single point ground very closely. To sample the oscillator waveform, the transistor
and 5kΩ potentiometer are used, and also can apply an adjustable ramp to ISENSE Pin.
2N
2222
RT
100K
E/A
ADJUST
4.7K
3 ISENSE
1K
ISENSE
ADJUST
1 COMP
2 VFB
4.7K
VREF
UTC
UC3842B/3843B
VREF 8
A
VC 7
V1
OUTPUT
OUTPUT 6
0.1
5K
4 RT/CT
CT
GND 5
0.1
1K/1W
Under Voltage Lockout
Under-Voltage Lock-Out: the output driver is biased to a high impedance state. To prevent activating the power
switch with output leakage current, Pin 6 should be shunted to ground with a bleeder resistor.
Error Amp Configuration
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LINEAR INTEGRATED CIRCUIT
APPLICATION INFORMATION(Cont.)
Current Sense Circuit
Peak current (IS) is equaled:
IS(MAX)=1.0V/RS
There should be a small RC filter to suppress switch transients.
Oscillator Waveforms and Maximum Duty Cycle
VREF
8
RT/RC
4
LARGE RT
SMALL CT
V4
RT
INTERINAL CLOCK
CT
GND
SMALL CT
LARGE RT
5
V4
INTERINAL CLOCK
CT (Oscillator timing capacitor) can be charged by VREF through RT and discharged by an internal current source.
At discharge time, the internal clock signal blanks the output to the low. Both oscillator frequency and maximum duty
cycle can be determined by Selection of RT and CT. All charge and discharge times can be calculated by the next
formulas:
tC=0.55 RT CT
 0.0063R T  2.7 

tD=RTCTIN 

 0.0063R T  4 
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LINEAR INTEGRATED CIRCUIT
APPLICATION INFORMATION(Cont.)
Shutdown Techniques
1KΩ
8
VREF
3
ISENSE
1
COMP
SHUTDOWN
330Ω
SHUTDOWN
500Ω
(Deadtime vs CT RT > 5kΩ)
TO CURRENT
SENSE-RESISTOR
The UTC UC3842B’s shutdown can be accomplished by two ways: raise Pin 3 above 1V; or pull Pin 1 below a
voltage two diode drops above ground. Either method can cause the PWM comparator’s output to be high. Because
the PWM latch is reset dominant, the output will remain low until the next clock cycle after the shutdown condition at
Pins 1 and/or 3 is removed.
Slope Compensation
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Percent Output Deadtime, %DT.
0
=2
CT
F
0p
nF
.0
=5
CT
0
=1
CT
Maximum Output Duty Cycle, Dmax (%)
nF
.0
=1
CT
nF
Timing Resistor, RT (KΩ)
TYPICAL CHARACTERISTICS
20mV/DIV
Discharge Current, Idischg (mA)

LINEAR INTEGRATED CIRCUIT
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
LINEAR INTEGRATED CIRCUIT
TYPICAL CHARACTERISTICS(Cont.)
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LINEAR INTEGRATED CIRCUIT
TYPICAL CHARACTERISTICS(Cont.)
Fig. 13 Output Saturation Voltage Versus Load Current
Source Saturation
(Load to Ground)
VCC
TA=25°C
-10
-20
VCC=15V
CL=1.0nF
TA=25°C
90
%
TA=-55°C
10
Sink Saturation
(Load to VCC)
10
%
GND
200
400
600
Output Load Current, IOUT (mA)
800
50ns/DIV
Fig. 16 Supply Current vs. Supply Voltage
Fig. 15 Output Cross Conduction
25
VCC=30V
CL=15pF
TA=25°C
100mA/DIV
Supply Current, ICC
Output Voltage, VO
0
TA=25°
C
20
15
10
UC3843B
20
TA=55°C
Supply Current, ICC (mA)
30
0
VCC=15V
80µs Pulsed Load
120Hz Rate
20V/DIV
Output Saturation Voltage, VSAT (V)
0
Fig. 14 Output Waveform
5
0
0
RT=10k
CT=3.3nF
VFB=0V
ISENSE=0V
TA=25°C
UC3842B

10
20
30
40
Supply Voltage, VCC (V)
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.
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