UC3845B

Features:

* Pb-Free Packages are Available
* 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 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


Pinout




Specifications




Description

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 components. These integrated circuits feature an oscillator, 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, 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 UC3844B, UC3845B 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 16 V (on) and 10 V (off), ideally suited for off-line converters. The UCX845B is tailored for lower voltage applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off).