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UC3846
SMPS Controller
Features
• Automatic Feed Forward Compensation
• Programmable Pulse by Pulse Current Limiting
• Automatic Symmetry Correction in Push-Pull
Configuration
• Enhanced Load Response Characteristics
• Parallel Operation Capability for Modulator Power
Systems
• Differential Current Sense Amplifier with Common Mode
Range
• Double Pulse Suppression
• 200mA Totem-Pole Outputs
•
±2%
Band gap Reference
• Under-Voltage Lockout
• Soft-Start Capability
• Shutdown Terminal
• 500KHz Operation
Description
The UC3846 control IC provides all of the necessary fea-
tures to implement fixed frequency, current mode control
schemes while maintaining a minimum external parts count.
The superior performance of this technique can be measured
in improved line regulation, enhanced load response char-
acteristics, and a simpler, easier-to-design control loop.
Topological advantages include inherent pulse-by-pulse cur-
rent limiting capability, automatic symmetry correction for
push-pull converters, and the ability to parallel “power
module
,,
while maintaining equal current sharing. Protection
circuitry includes built-in-under-voltage lockout and pro-
grammable current limit in addition to soft-start capability. A
shutdown function is also available which can initiate either
a complete shutdown with automatic restart or latch the
supply off. Other features include fully latched operation,
double pulse suppression, deadtime adjust capability, and
±2% trimmed bandgap reference. The UC3846 features low
outputs in the OFF state.
16-DIP
1
Internal Block Diagram
10
Rev. 5.0
©2000 Fairchild Semiconductor International
FAIRCHILD [ FAIRCHILD SEMICONDUCTOR ]
