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UC3845B

American First Semiconductor
Part Number UC3845B
Manufacturer American First Semiconductor
Description Controllers
Published Nov 11, 2014
Detailed Description High Performance Current Mode Controllers General Description UC3842B/3B/4B/5B,UC2842B/3B Package outline The UC3842B/...
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UC3845B
UC3845B

Overview
High Performance Current Mode Controllers General Description UC3842B/3B/4B/5B,UC2842B/3B Package outline The UC3842B/3B/4B/5B, 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 a trimmed oscillator for precise duty cycle control, 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, programmable output deadtime, and a latch for single pulse metering.
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.
The UCX842B has UVLO thresholds of 16 V (on) and 10 V (off), ideally suited for off–line converters.
The UCX843B is tailored for lower voltage applications having UVLO thresholds of 8.
5 V (on) and 7.
6 V (off).
Features • Trimmed Oscillator for Precise Frequency Control • Oscillator Frequency Guaranteed at 250 kHz • Current Mode Operation to 500 kHz • Automatic Feed Forward Compensation • Latching PWM for Cycle–By–Cycle Current Limiting • Internally Trimmed Reference with Undervoltage Lockout • High Current Totem Pole Output • Undervoltage Lockout with Hysteresis • Low Startup and Operating Current Vref 8(14) RT/CT 4(7) Voltage Feedback Input 2(3) Output Compensation 1(1) VCC 7(12) R 5.
0V Reference VCC Undervoltage Lockout R Vref Undervoltage Lockout Oscillator + Error Amplifier Latching PWM Gnd 5(9) Pin numbers in parenthesis are for the D suffix SO-14 package.
Figure 1.
Simplified Block Diagram VC 7(11...


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