Overview
The UC2845BN is a high-performance current mode PWM (Pulse Width Modulation) controller produced by STMicroelectronics. This IC is part of the UC284xB family, designed to implement off-line or DC to DC fixed frequency current mode control schemes with a minimal external parts count. It is particularly suited for medium power quasi-resonant ZVS (Zero Voltage Switching) flyback converters and can replace traditional melting fuses in automotive power distribution systems.
Key Specifications
| Parameter | Value | Unit |
|---|---|---|
| Supply Voltage (low impedance source) | 30 | V |
| Supply Voltage (Ii < 30mA) | 30 | V |
| Output Current | ±1 | A |
| Output Energy (capacitive load) | 5 | µJ |
| Analog Inputs (pins 2, 3) | –0.3 to 5.5 | V |
| Error Amplifier Output Sink Current | 10 | mA |
| Power Dissipation at Tamb ≤ 25 °C (Minidip) | 1.25 | W |
| Power Dissipation at Tamb ≤ 25 °C (SO8) | 800 | mW |
| Storage Temperature Range | –65 to 150 | °C |
| Junction Operating Temperature | –40 to 150 | °C |
| Lead Temperature (soldering 10s) | 300 | °C |
| Oscillator Frequency | 49 to 250 | KHz |
| Maximum Duty Cycle | 47 to 50% | % |
| Under-Voltage Lockout Start Threshold | 7.8 to 9.0 | V |
| Under-Voltage Lockout Minimum Operating Voltage After Turn-on | 7.0 to 8.2 | V |
Key Features
- Internally Trimmed Oscillator: Provides precise frequency control up to 250 kHz.
- Current Mode Operation: Supports operation up to 500 kHz.
- Automatic Feed Forward Compensation: Enhances stability and performance.
- Latching PWM for Cycle-by-Cycle Current Limiting: Ensures robust current control.
- Internally Trimmed Reference with Under-Voltage Lockout: Offers accurate voltage regulation and protection.
- High Current Totem Pole Output: Capable of sourcing or sinking high peak currents up to 1 A.
- Low Start-Up and Operating Current: Minimizes power consumption during start-up and operation.
- Programmable Oscillator Frequency and Duty Cycle: Allows for flexible design configurations using external resistors and capacitors.
Applications
- Off-Line and DC to DC Converters: Suitable for fixed frequency current mode control schemes.
- Automotive Power Distribution Systems: Can replace traditional melting fuses, enhancing reliability and efficiency.
- Quasi-Resonant ZVS Flyback Converters: Ideal for medium power applications requiring high efficiency and low noise.
- Industrial Power Supplies: Used in various industrial power supply designs requiring robust and efficient PWM control.
Q & A
- What is the maximum supply voltage for the UC2845BN?
The maximum supply voltage is 30 V.
- What is the range of the oscillator frequency for the UC2845BN?
The oscillator frequency can range from 49 kHz to 250 kHz.
- What is the maximum duty cycle for the UC2845BN?
The maximum duty cycle is between 47% and 50%.
- What is the under-voltage lockout start threshold for the UC2845BN?
The under-voltage lockout start threshold is between 7.8 V and 9.0 V.
- What is the minimum operating voltage after turn-on for the UC2845BN?
The minimum operating voltage after turn-on is between 7.0 V and 8.2 V.
- What is the maximum output current of the UC2845BN?
The maximum output current is ±1 A.
- How is the oscillator frequency programmed in the UC2845BN?
The oscillator frequency is programmed by connecting a resistor (RT) to Vref and a capacitor (CT) to ground.
- What type of applications is the UC2845BN suitable for?
The UC2845BN is suitable for off-line and DC to DC converters, automotive power distribution systems, and quasi-resonant ZVS flyback converters.
- What are the key features of the UC2845BN's output stage?
The output stage is a high current totem pole output capable of sourcing or sinking high peak currents up to 1 A.
- How does the UC2845BN handle current limiting?
The UC2845BN uses latching PWM for cycle-by-cycle current limiting.
