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What is UC3842B?

This electronic component, produced by the manufacturer "American First Semiconductor", performs the same function as "UC3842B/3B/4B/5B - High Performance Current Mode Controllers".


UC3842B Datasheet PDF - American First Semiconductor

Part Number UC3842B
Description UC3842B/3B/4B/5B - High Performance Current Mode Controllers
Manufacturers American First Semiconductor 
Logo American First Semiconductor Logo 


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High Performance Current Mode Controllers
General Description
UC3842B/3B/4B/5B,UC2842B/3B
Package outline
The UC3842B/3B/4B/5B, series are high performance fixed
frequency current mode controllers. They are specifically designed for
Off–Line and dc–to–dc converter applications offering the designer a
cost–effective solution with minimal external components. These
integrated circuits feature a trimmed oscillator for precise duty cycle
control, a temperature compensated reference, high gain error
amplifier, current sensing comparator, and a high current totem pole
output ideally suited for driving a power MOSFET.
Also included are protective features consisting of input and
reference undervoltage lockouts each with hysteresis, cycle–by–cycle
current limiting, programmable output deadtime, and a latch for single
pulse metering.
These devices are available in an 8–pin dual–in–line and surface
mount (SO–8) plastic package as well as the 14–pin plastic surface
mount (SO–14). The SO–14 package has separate power and ground
pins for the totem pole output stage.
The UCX842B has UVLO thresholds of 16 V (on) and 10 V (off),
ideally suited for off–line converters. The UCX843B is tailored for
lower voltage applications having UVLO thresholds of 8.5 V (on) and
7.6 V (off).
Features
Trimmed Oscillator for Precise Frequency Control
Oscillator Frequency Guaranteed at 250 kHz
Current Mode Operation to 500 kHz
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
Vref
8(14)
RT/CT
4(7)
Voltage
Feedback
Input
2(3)
Output
Compensation
1(1)
VCC 7(12)
R
5.0V
Reference
VCC
Undervoltage
Lockout
R
Vref
Undervoltage
Lockout
Oscillator
+
-
Error
Amplifier
Latching
PWM
Gnd 5(9)
Pin numbers in parenthesis are for the D suffix SO-14 package.
Figure 1. Simplified Block Diagram
VC
7(11)
Output
6(10)
Power
Ground
5(8)
Current
Sense
3(5) Input
8
1
8
1
DIP-8
SOP-8
14
1
SOP-14
Pin Connections
Compensation 1
Voltage Feedback 2
Current Sense 3
RT/CT 4
8 Vref
7 VCC
6 Output
5 Gnd
(Top View)
Compensation 1
NC 2
Voltage Feedback 3
NC 4
Current Sense 5
NC 6
RT/CT 7
14 Vref
13 NC
12 VCC
11 VC
10 Output
9 Gnd
8 Power Ground
(Top View)
@ 2010 Copyright By American First Semiconductor
Page 1/16

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UC3842B equivalent
UC3842B/3B/4B/5B,UC2842B/3B
2.55 V
2.50 V
VCC = 15 V
AV = -1.0
TA = 25°C
3.0 V
2.5 V
VCC = 15 V
AV = -1.0
TA = 25°C
2.45 V
0.5 µs/DIV
Figure 6. Error Amp Small Signal
Transient Response
2.0 V
1.0 µs/DIV
Figure 7. Error Amp Large Signal
Transient Response
100 0
VCC = 15 V
80
Gain
VO = 2.0 V to 4.0 V
RL = 100 K
30
TA = 25°C
60 60
40 90
Phase
20 120
0 150
-Ă20
10
180
100 1.0 k 10 k 100 k 1.0 M 10 M
f, FREQUENCY (Hz)
Figure 8. Error Amp Open Loop Gain and
Phase versus Frequency
0
ÄÄÄÄVCC = 15 V
-Ă4.0
-Ă8.0
ÄÄÄ-12
ÄÄÄÄ ÄÄÄTA=125°C
-16
TA = -55°C
ÄÄÄÄÄÄÄÄÄÄÄÄ-Ă20 TA=25°C
-Ă24
0
20 40 60 80 100 120
Iref, REFERENCE SOURCE CURRENT (mA)
Figure 10. Reference Voltage Change
versus Source Current
1.2
VCC = 15 V
1.0
0.8 TA = 25°C
0.6
TA = 125°C
0.4 TA = -55°C
0.2
0
0 2.0 4.0 6.0 8.0
VO, ERROR AMP OUTPUT VOLTAGE (V)
Figure 9. Current Sense Input Threshold
versus Error Amp Output Voltage
ÄÄÄÄÄÄ110
VCC = 15 V
RL 0.1
90
70
50
-Ă55
-Ă25
0
25 50 75 100 125
TA, AMBIENT TEMPERATURE (°C)
Figure 11. Reference Short Circuit Current
versus Temperature
www.First-semi.com
Page 5/16


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