5B High Performance Current Mode PWM Controller

Category: Electronics, Other Semiconductors, STMicroelectronics Inc

The UC2842B/3B/4B/5B and UC3842B/3B/4B/5B series are high-performance current mode Pulse Width Modulation (PWM) controllers designed for a wide range of power supply applications including off-line and DC-to-DC converters. The controllers offer numerous features making them suitable for high-performance power supply systems.

Main Features

The series boasts a precisely trimmed oscillator for accurate frequency control with a guaranteed oscillator frequency of 250 kHz, and the capability for current mode operation up to 500 kHz. An automatic feed-forward compensation is incorporated, along with a latching PWM to ensure cycle-by-cycle current limiting. The controllers are equipped with an internally trimmed reference and under-voltage lockout (UVLO) with hysteresis.

The controllers have a high current totem pole output, which can source or sink high peak current. It remains low when not in operation. Distinctions among the devices in the series include their UVLO thresholds and maximum duty cycle ranges. Specifically, the UC3842B and UC3844B offer UVLO thresholds ideal for off-line applications of 16V (on) and 10V (off), while the UC3843B and UC3845B are set at 8.5V and 7.9V respectively. The UC3842B and UC3843B are capable of operating with duty cycles close to 100%, whereas the UC3844B and UC3845B are restricted to a range from zero to 50% due to an internal toggle flip flop which disables the output every other clock cycle.

Description and Applications

These control ICs enable the implementation of off-line or DC-to-DC fixed-frequency current mode control schemes with minimal external components. Integrated features include an oscillator for precise duty cycle control, an under-voltage lockout with start-up current of less than 0.5 mA, a precision reference trimmed for accuracy, logic for latched operation, a PWM comparator with current limit control, and a totem pole output for N-Channel MOSFETs driving capability.

The block diagram provided demonstrates that the UC3844B and UC3845B incorporate a toggle flip flop not used in the other models. It indicates the flow and connection of the UVLO, VREF, internal bias, PWM latch, error amplifier, and current sense comparator within the controllers’ internal circuitry.

Packaging and Availability

These devices are available in standard Minidip and SO8 packaging options, allowing flexibility in hardware design and printed circuit board layout.

Device Information

Additional details regarding the device specifications and application notes are provided within the datasheet, with the release marked as March 1999 on the first page, suggesting the date of publication or latest revision for this document is March 1999.