UC2849N

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UC2849N is a Power Supply Controllers, Monitors developed by STMicroelectronics, which is higher performance,than their preceding products. The advantage of UC2849N lies in its low-noise output and its max output current which can be up to 1A. Its package type is TSSOP. Its application field includes telecom power system, motor control, DC/DC converters, portable battery powered tools, portable appliances and other energy Star level applications.

Working principle of UC2849N is the standard voltage mode pulse width modulation (PWM) technique. The feature of UC2849N allows the user to adjust the output voltage with a single external resistor. The UC2849 provides a modest amount of (300mA) gate drive current to drive either MOSFETs or IGBTs. It consists of an error amplifier, a high-voltage sink driver, an under voltage lockout circuit, an accurate reference, trimming facilities, overcurrent protection and soft-start capabilities.

The error amplifier uses an external resistor to establish a voltage reference and to sense the output voltage. The output voltage is compared to the reference voltage. The error amplifier drives the sink (high-side) FET for the power supply. A power-ON reset circuit includes an under-voltage lockout, to protect the always-on part of the circuit. The on-SO pin is reset when the voltage drops below the UVLO threshold, eliminating the need for a separate reset circuit. An internal comparator serves to sense the current in the sink driver FET, which is typically set at 1/2 of the peak switch current. When the current through the internal resistor equals the current setpoint, the internal comparator output turns off the high-side FET, and pulls the high-side gate low.

UC2849N works with a trimming resistor connected between the Fine Trim (FT) and the ground. The fine trim is a digital input for trimming the output voltage for precision regulation. This consists of a digitally adjustable, voltage divider. When the fine-trim pin is LOW, the voltage divider is disconnected from the Error Amplifier input, allowing the Error Amplifier to regulate the output voltage, based on the reference voltage. When the fine-trim pin is HIGH, the voltage divider is connected, causing the output voltage to be regulated to the value determined by the ratio of the two resistors. This feature is normally used to adjust the output voltage after the initial start up.

In addition, UC2849N incorporates a Soft-Start circuit, which allows the user to control the start-up ramp rate of the power supply output. The Soft Start enables the power supply output to ramp up at a controlled rate to prevent the inrush and disruption associated with an abrupt start-up. The Soft-Start pin determines the start-up ramp time. With a resistor from SS to ground, the voltage on the pin ramps up, thus controlling the Soft-Start time. When the voltage at the Soft-Start pin reaches 2V, the SS pin elevates the over-current threshold internally, allowing the device to enter “normal operation” of the power supply.

Due to its cost-effective solutions and wide range of features, UC2849N can be an ideal choice for motor control, DC/DC converters, portable battery powered tools, portable appliances and other energy Star level applications.

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