UC3845 Fairchild SMPS Controller Data Sheet
Download Datasheet for Fairchild Semiconductor UC3845 SMPS Controller [12 pages Rev.1.0.1 2002 pdf/zip]
Description
The UC3845 are fixed frequencycurrent-mode PWM controller. They are specially designed for Off-Line and DC to DC converter applications with minimum external components. These integrated circuits feature a trimmed oscillator for precise duty cycle control, a temperature compensated reference, high gain error amplifier, current sensing comparator and a high current totempole output for driving a Power MOSFET.
The UC3845 have UVLO thresholds of 8.5V(on) and 7.9V (off).
The UC3845 can operate with 50% duty cycle.
FEATURES
– Low Start up Current
– Maximum Duty Clamp
– UVLO With Hysteresis
– Operating Frequency up to 500KHz
DATASHEET CONTAINS:
INTERNAL BLOCK DIAGRAM
UC3845 PINOUT
ABSOLUTE MAXIMUM RATINGS
POWER DISSIPATION CURVE
THERMAL DATA
PIN ARRAY
ELECTRICAL CHARACTERISTICS
– Reference Section
– Oscillator Section
– Error Amplifier Section
– Current Sense Section
– Output Section
– Under-Voltage Lockout Section
– PWM Section
– Total Standby Current
Figure 1. Open Loop Test Circuit
Figure 2. Under Voltage Lockout
Figure 3. Error Amp Configuration
Figure 4. Current Sense Circuit
Figure 5. Oscillator Waveforms and Maximum Duty Cycle
Figure 6. Oscillator Dead Time & Frequency
Figure 7. Timing Resistance vs Frequency
Figure 8. Shutdown Techniques
Figure 9. Slope Compensation
Figure 10. Temperature Drift (Vref)
Figure 11. Temperature Drift (Ist)
Figure 12. Temperature Drift (Icc)
MECHANICAL DIMENSIONS
ORDERING INFORMATION
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