UC3844ADTR Integrated Circuits (ICs)

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The UC3844ADTR series ICs are members of the constant frequency pulse-width modulation (PWM) family of voltage controllers. This economical line of devices is designed to help simplify system design, reduce parts count, and lower external component costs. The pin-to-pin compatible UC3845ADTR series is available in eight-pin miniDIP and SOIC packages, and provides the newest technology to optimize system performance in DC-DC switching controllers.

The UC3844ADTR family is suitable for many monolithic synchronous and non-synchronous applications. Its versatile range of features includes TTL-compatible logic inputs, synchronization of the oscillator, voltage-controlled operation, and pulse-by-pulse current limiting.

The UC3844ADTR series implements a unique, variable-on-time, variable-off-time technique for maintaining stable voltage regulation over a wide range of supply and load conditions. This approach helps to simplify line and load regulation. Internally implemented leading-edge blanking of the voltage-feedback input eliminates false triggering due to spike noise. Other features include a high-gain error-amplifier, a complex digital network full of special functions, and other features.

Applications

The UC3844ADTR devices provide excellent DC-DC conversion with low memory effects. This makes them ideal for applications such as switching power supplies, battery chargers, isolated DC-DC converters and other power-systems applications.

Working Principle

The UC3844ADTR IC employs a unique on-time, off-time approach for maintaining stable voltage regulation over a wide range of supply and load conditions. During the on-time, it turns conducting elements on and off such as the MOSFETs and then ramps up the voltage. During the off-time, the current decreases and the voltage is determined by the feedback loop. The operating frequency is affected by the total on-time of the FETs. The IC is capable of operating from 200 KHz to 500 KHz.

Additionally, an external current sense resistor is used to sense the inductor current and provide "Pulse-by-Pulse" current limiting capability. Frequency fold-back is provided as an integral part of the UC3844ADTR IC to further reduce inductor current ripple at heavy loads. An externally adjustable 5.1V reference can be used in some designs. Otherwise, an internal 5.1V reference is integrated in the IC.

The UC3844ADTR provides a number of features including low start-up and operating current, a low standby current, a low external parts count, and a high efficiency over a wide range of load and supply conditions. These features enable the design of small, lightweight, cost-effective switching power supplies.

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