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UC2844N Datasheet PDF : 14 Pages
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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%.
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).
• 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
Vref
8(14)
RTCT
4(7)
Voltage
Feedback
2(3)
1(1)
Output
Comp.
Simplified Block Diagram
VCC 7(12)
R
5.0V
Reference
VCC
Undervoltage
Lockout
R
Vref
Undervoltage
Lockout
Oscillator
+
–
Error
Amplifier
Flip
Flop
&
Latching
PWM
VC
7(11)
Output
6(10)
PWR GND
5(8)
Current
Sense
3(5)
Gnd 5(9)
Pin numbers in parenthesis are for the D suffix SO–14 package.
UC3844, 45
UC2844, 45
HIGH PERFORMANCE
CURRENT MODE
CONTROLLERS
N SUFFIX
PLASTIC PACKAGE
CASE 626
8
D SUFFIX
PLASTIC PACKAGE
CASE 751A
(SO–14)
1
14
1
PIN CONNECTIONS
Compensation 1
Voltage Feedback 2
Current Sense 3
RT/CT 4
8 Vref
7 VCC
6 Output
5 Gnd
(Top View)
Compensation 1
NC 2
Voltage Feedback 3
NC 4
Current Sense 5
NC 6
14 Vref
13 NC
12 VCC
11 VC
10 Output
9 Gnd
RT/CT 7
8 Power Ground
(Top View)
ORDERING INFORMATION
Device
Operating
Temperature Range
Package
UC3844D
SO–14
UC3845D
UC3844N
TA = 0° to +70°C
SO–14
Plastic
UC3845N
Plastic
UC2844D
SO–14
UC2845D
UC2844N
TA = – 25° to +85°C
SO–14
Plastic
UC2845N
Plastic
MOTOROLA ANALOG IC DEVICE DATA
© Motorola, Inc. 1996
Rev 1
1
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