UC3844, UC3845, UC2844,
UC2845
High Performance
Current Mode Controllers
The UC3844, UC3845 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 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 dead
times to be programmed for 50% to 70%.
These devices are available in an 8−pin dual−in−line 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 UCX844 has UVLO thresholds of 16 V (on) and 10 V (off),
ideally suited for off−line converters. The UCX845 is tailored for
lower voltage applications having UVLO thresholds of 8.5 V (on) and
7.6 V (off).
Features
http://onsemi.com
PDIP−8
N SUFFIX
CASE 626
1
14
1
8
1
SOIC−14
D SUFFIX
CASE 751A
SOIC−8
D1 SUFFIX
CASE 751A
8
PIN CONNECTIONS
Compensation 1
Voltage Feedback 2
Current Sense 3
R
T
/C
T
4
(Top View)
8
7
6
5
V
ref
V
CC
Output
GND
•
•
•
•
•
•
•
•
•
•
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
Input Undervoltage Lockout with Hysteresis
Low Startup and Operating Current
Direct Interface with ON Semiconductor SENSEFETt Products
Pb−Free Packages are Available
V
CC
V
ref
8(14)
R
R
R
T
C
T
4(7)
V
ref
Undervoltage
Lockout
Oscillator
Flip
Flop
&
Latching
PWM
5.0V
Reference
7(12)
Compensation
NC
Voltage Feedback
NC
Current Sense
NC
R
T
/C
T
1
2
3
4
5
6
7
(Top View)
14 V
ref
13 NC
12 V
CC
11 V
C
10 Output
9
8
GND
Power Ground
V
CC
Undervoltage
Lockout
V
C
7(11)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 14 of this data sheet.
Output
6(10)
PWR GND
5(8)
Current
Sense
3(5)
Voltage
Feedback
2(3)
1(1)
Output
Comp.
+
−
DEVICE MARKING INFORMATION
See general marking information in the device marking
section on page page 14 of this data sheet.
Error
Amplifier
GND 5(9)
Pin numbers in parenthesis are for the D suffix SOIC−14 package.
Figure 1. Simplified Block Diagram
©
Semiconductor Components Industries, LLC, 2006
July, 2006
−
Rev. 7
1
Publication Order Number:
UC3844/D
ONSEMI [ ON SEMICONDUCTOR ]
