Overview
The UC3845J is a current-mode PWM (Pulse Width Modulation) controller integrated circuit produced by Unitrode, now part of Texas Instruments. This component is specifically designed for off-line and DC-to-DC converter applications, requiring minimal external components. It features a trimmed oscillator for precise duty cycle control, a temperature-compensated reference, a high-gain error amplifier, and a current sensing comparator. The UC3845J is widely used in power supply systems due to its robust and efficient design.
Key Specifications
| Parameter | Symbol | Value | Unit |
|---|---|---|---|
| Supply Voltage | VCC | 30 | V |
| Output Current | IO | ±1 | A |
| Analog Inputs (Pin 2, 3) | V(ANA) | -0.3 to 6.3 | V |
| Error Amp Output Sink Current | ISINK (E.A) | 10 | mA |
| Power Dissipation at TA≤25°C (8DIP) | PD | 1200 | mW |
| Storage Temperature Range | TSTG | -65 ~ +150 | °C |
| Oscillation Frequency | f | 47 to 57 | kHz |
| Maximum Duty Cycle | D(Max) | 47 to 50% | % |
| Start-Up Current | IST | 0.45 to 1 | mA |
| Operating Supply Current | ICC(OPR) | 14 to 17 | mA |
Key Features
- Trimmed oscillator for precise duty cycle control
- Temperature-compensated reference
- High-gain error amplifier
- Current sensing comparator
- High current totem-pole output for driving a Power MOSFET
- Low start-up current
- Maximum duty cycle clamp
- Under-voltage lockout (UVLO) with hysteresis
- Operating frequency up to 500 kHz
Applications
The UC3845J is primarily used in off-line and DC-to-DC converter applications. It is suitable for a variety of power supply systems, including:
- Switch-mode power supplies
- DC-to-DC converters
- High-frequency power supplies
- Power factor correction circuits
Q & A
- What is the primary function of the UC3845J?
The UC3845J is a current-mode PWM controller designed for off-line and DC-to-DC converter applications.
- What is the maximum supply voltage for the UC3845J?
The maximum supply voltage is 30V.
- What is the typical operating frequency range of the UC3845J?
The typical operating frequency range is 47 to 57 kHz.
- Does the UC3845J have under-voltage lockout (UVLO) protection?
- What is the maximum duty cycle for the UC3845J?
The maximum duty cycle is 47 to 50%.
- What type of output does the UC3845J have?
The UC3845J has a high current totem-pole output for driving a Power MOSFET.
- What are the typical start-up and operating supply currents for the UC3845J?
The start-up current is 0.45 to 1 mA, and the operating supply current is 14 to 17 mA.
- What is the storage temperature range for the UC3845J?
The storage temperature range is -65°C to +150°C.
- Can the UC3845J operate at 100% duty cycle?
No, the UC3845J can operate with a maximum duty cycle of 50%.
- What are some common applications of the UC3845J?
Common applications include switch-mode power supplies, DC-to-DC converters, high-frequency power supplies, and power factor correction circuits.
