UC3844B, UC3845B,
UC2844B, UC2845B
High Performance
Current Mode Controllers
The UC3844B, UC3845B series are high performance fixed
frequency current mode controllers. They are specifically designed for
Off−Line and dc−dc converter applications offering the designer a
cost−effective solution with minimal external components. These
integrated circuits feature an oscillator, 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.
http://onsemi.com
PDIP−8
N SUFFIX
CASE 626
8
1
Also included are protective features consisting of input and
reference undervoltage lockouts each with hysteresis, cycle−by−cycle
current limiting, a latch for single pulse metering, and a flip−flop
which blanks the output off every other oscillator cycle, allowing
output deadtimes to be programmed from 50% to 70%.
SOIC−8
D1 SUFFIX
CASE 751
8
1
These devices are available in an 8−pin dual−in−line and surface
mount (SOIC−8) plastic package as well as the 14−pin plastic surface
mount (SOIC−14). The SOIC−14 package has separate power and
ground pins for the totem pole output stage.
The UCX844B has UVLO thresholds of 16 V (on) and 10 V (off),
ideally suited for off−line converters. The UCX845B is tailored for
lower voltage applications having UVLO thresholds of 8.5 V (on) and
7.6 V (off).
SOIC−14
D SUFFIX
CASE 751A
14
1
PIN CONNECTIONS
Features
1
2
3
4
8
7
6
5
Compensation
Voltage Feedback
Current Sense
V
V
ref
CC
• Pb−Free Packages are Available
Output
• Trimmed Oscillator for Precise Frequency Control
• Oscillator Frequency Guaranteed at 250 kHz
• Current Mode Operation to 500 kHz Output Switching Frequency
• Output Deadtime Adjustable from 50% to 70%
• Automatic Feed Forward Compensation
• Latching PWM for Cycle−By−Cycle Current Limiting
• Internally Trimmed Reference with Undervoltage Lockout
• High Current Totem Pole Output
R /C
T
GN
D
T
(Top View)
Compensation
1
2
3
4
5
6
7
14
13
12
11
10
9
V
ref
NC
Voltage Feedback
NC
NC
V
V
CC
C
Current Sense
NC
Output
GND
8
R /C
T
Power Ground
T
• Undervoltage Lockout with Hysteresis
• Low Startup and Operating Current
(Top View)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 2 of this data sheet.
DEVICE MARKING INFORMATION
See general marking information in the device marking
section on page 16 of this data sheet.
Semiconductor Components Industries, LLC, 2004
1
Publication Order Number:
September, 2004 − Rev. 3
UC3844B/D