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.
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%.
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).
Features
http://onsemi.com
8
1
PDIP−8
N SUFFIX
CASE 626
8
1
SOIC−8
D1 SUFFIX
CASE 751
14
1
SOIC−14
D SUFFIX
CASE 751A
PIN CONNECTIONS
Compensation
Voltage Feedback
Current Sense
R
T
/C
T
1
2
3
4
8
7
6
5
•
•
•
•
•
•
•
•
•
•
•
Pb−Free Packages are Available
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
Undervoltage Lockout with Hysteresis
Low Startup and Operating Current
(Top View)
Compensation
NC
Voltage Feedback
NC
Current Sense
NC
R
T
/C
T
1
2
3
4
5
6
7
14
13
12
11
10
9
8
V
ref
V
CC
Output
GN
D
V
ref
NC
V
CC
V
C
Output
GND
Power Ground
(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
September, 2004 − Rev. 3
Publication Order Number:
UC3844B/D
ONSEMI [ ON SEMICONDUCTOR ]
