Order this document by UC3844/D
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 deadtimes to be programmed for
50% to 70%.
N SUFFIX
PLASTIC PACKAGE
CASE 626
8
1
D SUFFIX
These devices are available in an 8–pin dual–in–line 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 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).
PLASTIC PACKAGE
14
CASE 751A
(SO–14)
1
PIN CONNECTIONS
• 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 Motorola SENSEFET Products
Compensation
Voltage Feedback
Current Sense
1
2
8
7
V
ref
V
CC
3
4
6
5
Output
Gnd
R
/C
T
T
(Top View)
1
14
13
Compensation
NC
V
ref
2
NC
3
4
12
11
Voltage Feedback
NC
V
V
CC
C
5
6
10
9
Current Sense
NC
Output
Gnd
Simplified Block Diagram
R
/C
7
8
Power Ground
T
T
V
7(12)
CC
(Top View)
V
V
CC
ref
8(14)
5.0V
Reference
Undervoltage
Lockout
ORDERING INFORMATION
Operating
R
R
V
ref
V
C
Undervoltage
Lockout
Temperature Range
Device
Package
SO–14
SO–14
Plastic
Plastic
SO–14
SO–14
Plastic
Plastic
7(11)
UC3844D
UC3845D
UC3844N
UC3845N
UC2844D
UC2845D
UC2844N
UC2845N
R
4(7)
C
Output
6(10)
T
T
Flip
Flop
&
Latching
PWM
Oscillator
T
= 0° to +70°C
A
Voltage
Feedback
PWR GND
5(8)
+
–
2(3)
Current
Sense
3(5)
Error
Amplifier
1(1)
Output
Comp.
T
= – 25° to +85°C
A
Gnd
5(9)
Pin numbers in parenthesis are for the D suffix SO–14 package.
Motorola, Inc. 1996
Rev 1
1
MOTOROLA ANALOG IC DEVICE DATA