UC3845AN

The UC3845AN is a high-performance, fixed-frequency current-mode pulse-width modulation (PWM) controller designed for use in power supply applications. Manufactured by Texas Instruments, this integrated circuit is particularly well-suited for off-line and DC-DC converter applications, including switch-mode power supplies (SMPS).

Key Features:

1. Current-Mode Control: The UC3845AN employs current-mode control, which enhances the stability and transient response of the power supply. This feature allows for easier implementation of overcurrent protection and provides inherent cycle-by-cycle current limiting.

2. Fixed Frequency Operation: The device operates at a fixed frequency, typically around 100 kHz, which simplifies the design of the output filter and minimizes the size of passive components.

3. Voltage Reference: It includes a precision voltage reference, typically around 2.5V, which is used for feedback and regulation purposes. This reference ensures stable operation and accurate output voltage regulation.

4. Output Drivers: The UC3845AN features totem-pole output drivers capable of sourcing and sinking significant current, allowing for direct driving of power MOSFETs. This capability reduces the need for additional driver circuits, simplifying the overall design.

5. Soft Start: The device incorporates a soft-start feature that gradually ramps up the output voltage, reducing inrush current and preventing overshoot during startup.

6. Protection Features: The UC3845AN includes several protection features, such as under-voltage lockout (UVLO), which prevents the device from operating until the supply voltage exceeds a certain threshold, and thermal shutdown to protect against overheating.

7. Package Type: The "AN" suffix indicates that the UC3845 is available in a standard 8-pin DIP (Dual In-line Package) form factor, making it easy to integrate into various circuit designs.

Applications:

The UC3845AN is widely used in various applications, including:

• Off-line power supplies for consumer electronics
• DC-DC converters for telecommunications
• Battery chargers
• Industrial power supplies
• LED drivers

Electrical Characteristics:

• Supply Voltage Range: Typically operates from 8V to 30V.
• Output Voltage: The output voltage can be adjusted based on external feedback components.
• Temperature Range: The device is rated for operation over a wide temperature range, typically from -40°C to +125°C.

Conclusion:

The UC3845AN from Texas Instruments is a versatile and reliable PWM controller that provides essential features for efficient power management in a variety of applications. Its combination of current-mode control, fixed frequency operation, and built-in protection mechanisms makes it a popular choice among engineers designing power supply circuits.