Order this document by UC3844B/D
The UC3844B, UC3845B 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.
HIGH PERFORMANCE
CURRENT MODE
CONTROLLERS
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%.
N SUFFIX
PLASTIC PACKAGE
CASE 626
8
1
These devices are available in an 8–pin dual–in–line and surface mount
(SO–8) 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.
D1 SUFFIX
PLASTIC PACKAGE
CASE 751
8
(SO–8)
1
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).
D SUFFIX
PLASTIC PACKAGE
CASE 751A
14
1
(SO–14)
• 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
PIN CONNECTIONS
V
1
2
3
4
8
7
6
5
Compensation
Voltage Feedback
Current Sense
ref
V
CC
Output
Gnd
R
/C
T
T
(Top View)
• Undervoltage Lockout with Hysteresis
• Low Startup and Operating Current
Compensation
1
2
3
4
5
14
13
12
11
10
9
V
ref
NC
Voltage Feedback
NC
NC
V
CC
V
C
Current Sense
NC
Output
Gnd
6
7
Simplified Block Diagram
8
R
/C
Power Ground
T
T
V
7(12)
CC
(Top View)
ORDERING INFORMATION
Operating
V
CC
5.0V
Reference
V
Undervoltage
Lockout
ref
8(14)
R
R
Device
Package
Temperature Range
V
ref
Undervoltage
Lockout
V
C
UC384XBD
UC384XBD1
UC384XBN
UC284XBD
UC284XBD1
UC284XBN
UC384XBVD
UC384XBVD1
UC384XBVN
SO–14
SO–8
7(11)
T
= 0° to + 70°C
A
Output
6(10)
Plastic
SO–14
SO–8
R
/C
T
Oscillator
T
4(7)
Latching
PWM
Power
Ground
T
= – 25° to + 85°C
Voltage
Feedback
Input
A
5(8)
3(5)
Plastic
SO–14
SO–8
2(3)
1(1)
Error
Amplifier
Current
Sense Input
Output/
Compensation
T
= – 40° to +105°C
A
Plastic
Gnd
5(9)
X indicates either a 4 or 5 to define specific device
part numbers.
Pin numbers in parenthesis are for the D suffix SO–14 package.
Motorola, Inc. 1996
Rev 1
1
MOTOROLA ANALOG IC DEVICE DATA