The UC3842/3/4/5 series are highly featured current mode PWM controllers optimized for off-line and DC-to-DC converters. Key features include a low start-up current of less than 1mA, automatic feed forward compensation, pulse-by-pulse current limiting, enhanced load response characteristics, and under-voltage lockout with hysteresis. The series is tailored for superior performance in power management applications and are distinguished by their under-voltage lockout thresholds and maximum duty cycle ranges.
Main Features
The UC3842/3/4/5 ICs are engineered for low power startup, consuming less than 1mA. They exhibit exceptional load response characteristics and incorporate an integral feature that eliminates double pulses. The devices house an internally trimmed bandgap reference, ensuring precise operation. With a high-current totem pole output compatible with driving N-Channel MOSFETs, these ICs are designed to be efficient while in the off-state. Operating at up to 500 kHz, the UC3842/3/4/5 aid in creating power-efficient designs.
Variations and Applications
The different models within this family cater to various application requirements. The UC3842 and UC3844 are well-suited for off-line applications due to their UVLO thresholds of 16V (on) and 10V (off). Contrastingly, the UC3843 and UC3845 are designed with lower UVLO thresholds of 8.5V (on) and 7.9V (off), making them suitable for diverse uses. Additionally, the UC3842 and UC3843 models can achieve duty cycles close to 100%, whereas the UC3844 and UC3845 are set to reach a range of 0 to 50% duty cycle, attributable to an internal toggle flip flop that gates the output on alternate cycles.
Block Diagram Insights
The block diagram highlights the complexity of the IC, showcasing features such as a PWM comparator with current limit control, a power ground, and an error amplifier. The diagram indicates the presence of a totem pole output stage, an under-voltage lockout (UVLO) circuit, and an internally biased ground. The UC3844 and UC3845 variants include a toggle flip flop, demarcating them from the UC3842 and UC3843.
Product Information and Availability
This data brief reflects the state of the UC3842/3/4/5 series as of October 1991, with the information being a succinct fragment of the comprehensive specifications found in the Linear & Switching Voltage Regulators Application Manual. These current mode PWM controllers are available in standard packages and are identified using the descriptor ‘CURRENT MODE PWM CONTROLLER’.
Note: For detailed specifications, refer to the manufacturer’s application manual with the order code AMLISVOREST/1.
References:
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