
Semiconductor Components Industries, LLC, 2005
November, 2005 Rev. 7
1
Publication Order Number:
UC3842B/D
UC3842B, UC3843B,
UC2842B, UC2843B,
NCV3843BV
High Performance Current
Mode Controllers
The UC3842B, UC3843B series are high performance fixed
frequency current mode controllers. They are specifically designed for
OffLine and DCDC converter applications offering the designer a
costeffective 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, cyclebycycle
current limiting, programmable output deadtime, and a latch for single
pulse metering.
These devices are available in an 8pin dualinline and surface
mount (SOIC8) plastic package as well as the 14pin plastic surface
mount (SOIC14). The SOIC14 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 offline 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 CycleByCycle Current Limiting
Internally Trimmed Reference with Undervoltage Lockout
High Current Totem Pole Output
Undervoltage Lockout with Hysteresis
Low Startup and Operating Current
PbFree Packages are Available
Figure 1. Simplified Block Diagram
5.0V
Reference
Latching
PWM
V
CC
Undervoltage
Lockout
Oscillator
Error
Amplifier
7(12)
V
C
7(11)
Output
6(10)
Power
Ground
5(8)
3(5)
Current
Sense
Input
V
ref
8(14)
4(7)
2(3)
1(1)
GND
5(9)
R
T
/C
T
Voltage
Feedback
Input
R
R
+
V
ref
Undervoltage
Lockout
Output
Compensation
Pin numbers in parenthesis are for the D suffix SOIC14 package.
V
CC
14
SOIC14
D SUFFIX
CASE 751A
1
See detailed ordering and shipping information in the package
dimensions section on page 16 of this data sheet.
ORDERING INFORMATION
See general marking information in the device marking
section on page 18 of this data sheet.
DEVICE MARKING INFORMATION
1
8
PDIP8
N SUFFIX
CASE 626
PIN CONNECTIONS
Compensation
NC
Voltage Feedback
NC
Current Sense
NC
R
T
/C
T
Compensation
Voltage Feedback
Current Sense
R
T
/C
T
V
ref
V
CC
Output
GND
V
ref
NC
V
CC
V
C
Output
GND
Power Ground
(Top View)
8
7
6
5
1
2
3
4
1
2
3
4
14
13
12
11
5
6
7
10
9
8
(Top View)
SOIC8
D1 SUFFIX
CASE 751
1
8
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