Product Description
Description
The UC1842/3/4/5 family of control devices provides the necessary features to implement off-line or dc-to-dc fixed frequency current mode control schemes with a minimal external parts count. Internally implemented circuits include under-voltage lockout featuring start up current less than 1 mA, a precision reference trimmed for accuracy at the error amp input, logic to insure latched operation, a PWM comparator which also provides current limit control, and a totem pole output stage designed to source or sink high peak current. The output stage, suitable for driving N-Channel MOSFETs, is low in the off state.
Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. The UC1842 and UC1844 have UVLO thresholds of 16 VON and 10 VOFF, ideally suited to off-line applications. The corresponding thresholds for the UC1843 and UC1845 are 8.4 V and 7.6 V. The UC1842 and UC1843 can operate to duty cycles approaching 100%. A range of zero to 50% is obtained by the UC1844 and UC1845 by the addition of an internal toggle flip flop which blanks the output off every other clock cycle.
Features
Optimized For Off-line and DC-to-DC Converters
Low Start-Up Current (<1 mA)
Automatic Feed ForwardCompensation
Pulse-by-Pulse Current Limiting
Enhanced Load Response Characteristics
Under-Voltage Lockout With Hysteresis
Double Pulse Suppression
High Current Totem Pole Output
Internally Trimmed Bandgap Reference
500-kHz Operation
Low RO Error Amp
Parametrics View all products in PWM and Resonant Controller
Topology
Control Method
Duty Cycle (Max) (%)
Frequency (Max) (kHz)
UVLO Thresholds On/Off (V)
Regulated Outputs (#)
Special Features
Rating
Operating Temperature Range (C)
Pin/Package
UC3843 UC1843 UC2843
Boost
Buck
Flyback
Forward Boost
Flyback
Forward Boost
Flyback
Forward
Current Current Current
100 100 100
450 450 450
8.4/7.6 8.4/7.6 8.4/7.6
1 1 1
Error Amplifier Error Amplifier Error Amplifier
Military Military Military
0 to 70 -55 to 125 -40 to 85
14SOIC
8PDIP
8SOIC 14CFP
20LCCC
8CDIP 14SOIC
8PDIP
8SOI
