UC3845B Datasheet Text
High Performance Current Mode Controllers
UC3844B, UC3845B, UC2844B, UC2845B
The UC3844B, UC3845B series are high performance fixed frequency current mode controllers. They are specifically designed for Off- Line and dc- dc converter applications offering the designer a cost- effective solution with minimal external ponents. These integrated circuits feature an oscillator, a temperature pensated reference, high gain error amplifier, current sensing parator, 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 from 50% to 70%.
These devices are available in an 8- pin dual- in- line and surface mount (SOIC- 8) plastic package as well as the 14- pin plastic surface mount (SOIC- 14). The SOIC- 14 package has separate power and ground pins for the totem pole output stage.
The UCX844B has UVLO thresholds of 16V (on) and 10V (off), ideally suited for off- line converters. The UCX845B is tailored for lower voltage applications having UVLO thresholds of 8.5V (on) and 7.6V (off).
Features
- Trimmed Oscillator for Precise Frequency Control
- Oscillator Frequency Guaranteed at 250 kHz
- Current Mode Operation to 500 kHz Output Switching Frequency
- Output Deadtime Adjustable from 50% to 70%
- Automatic Feed Forward pensation
- 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
- These Devices are...
