Overview
The UC3845D is a fixed frequency current-mode PWM (Pulse Width Modulation) controller produced by Fairchild Semiconductor. It is specifically designed for off-line and DC-to-DC converter applications, requiring a minimum number of external components. This integrated circuit features a trimmed oscillator for precise duty cycle control, a temperature-compensated reference, a high-gain error amplifier, a current sensing comparator, and a high-current totem-pole output stage for driving N-channel MOSFETs.
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 (14-SOP) | PD | 680 | 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 | < 1 | mA |
| Operating Supply Current | ICC(OPR) | 14 to 17 | mA |
Key Features
- Low start-up current (< 1mA)
- Undervoltage lockout (UVLO) with hysteresis (8.5V on, 7.9V off)
- Operating frequency up to 500kHz
- Internally trimmed bandgap reference
- Error amplifier with low output resistance
- Pulse-by-pulse current limiting
- Double-pulse suppression
- High-current totem-pole output for driving N-channel MOSFETs
- Automatic feedforward compensation
- Enhanced load-response characteristics
Applications
The UC3845D is designed for use in off-line and DC-to-DC converter applications. It is particularly suitable for power supplies that require high efficiency, precision, and reliability. These applications include:
- Off-line power supplies
- DC-to-DC converters
- Switch-mode power supplies
- High-frequency power conversion systems
Q & A
- What is the primary function of the UC3845D?
The UC3845D is a fixed frequency current-mode PWM controller designed for off-line and DC-to-DC converter applications.
- What is the operating frequency range of the UC3845D?
The UC3845D can operate up to a frequency of 500kHz.
- What are the UVLO thresholds for the UC3845D?
The UVLO thresholds for the UC3845D are 8.5V (on) and 7.9V (off).
- What is the maximum duty cycle for the UC3845D?
The maximum duty cycle for the UC3845D is 50%.
- What is the start-up current of the UC3845D?
The start-up current of the UC3845D is less than 1mA.
- What type of output stage does the UC3845D have?
The UC3845D has a high-current totem-pole output stage designed for driving N-channel MOSFETs.
- What are the key features of the error amplifier in the UC3845D?
The error amplifier in the UC3845D has low output resistance and high gain.
- What is the storage temperature range for the UC3845D?
The storage temperature range for the UC3845D is -65°C to +150°C.
- What are the typical applications of the UC3845D?
The UC3845D is typically used in off-line power supplies, DC-to-DC converters, and other switch-mode power supplies.
- What package options are available for the UC3845D?
The UC3845D is available in a 14-pin SOIC (D) package.
