Overview
The UC3842D8 is a single-ended current-mode PWM controller from Texas Instruments, designed for off-line and DC-to-DC converters. It is part of the UCx84x family of control integrated circuits, which provide the necessary features to implement fixed-frequency current-mode control schemes with a minimum number of external components.
This IC is optimized for efficient power sequencing and is particularly suited for driving N-channel MOSFETs or bipolar power transistors. It features a low start-up current of less than 1 mA, making it efficient for bootstrapping from the rectified input of an off-line converter.
Key Specifications
| Parameter | Value |
|---|---|
| Package | SOIC (D) - 8 pins |
| Operating Temperature Range | 0°C to 70°C |
| Oscillator Frequency | 100 kHz to 500 kHz |
| Maximum Duty Cycle | Approximately 100% |
| Start-up Current | < 1 mA |
| UVLO Thresholds | Turn-on: 16V, Turn-off: 10V |
| Output Current | ± 1 A peak, + 200 mA average |
Key Features
- Optimized for off-line and DC-to-DC converters
- Low start-up current (< 1 mA)
- Automatic feedforward compensation
- Pulse-by-pulse current limiting
- Enhanced load-response characteristics
- Undervoltage lockout with hysteresis
- Double-pulse suppression
- High-current totem-pole output
- Internally trimmed bandgap reference
- Up to 500 kHz operation
- Error amplifier with low output resistance
Applications
- Switching regulators of any polarity
- Transformer-coupled DC-DC converters
- Off-line power supplies
- DC-DC converters
- Flyback and forward converters
Q & A
- What is the operating temperature range of the UC3842D8?
The operating temperature range is from 0°C to 70°C.
- What is the maximum oscillator frequency of the UC3842D8?
The maximum oscillator frequency is 500 kHz.
- What is the start-up current of the UC3842D8?
The start-up current is less than 1 mA.
- What are the UVLO thresholds for the UC3842D8?
The turn-on threshold is 16V, and the turn-off threshold is 10V.
- What is the maximum duty cycle of the UC3842D8?
The maximum duty cycle is approximately 100%.
- How is the current sensing and limiting configured in the UC3842D8?
Current-to-voltage conversion is done externally with a ground-referenced resistor Rs, controlled by the error amplifier.
- Can the UC3842D8 be synchronized to an external clock source?
- What type of output stage does the UC3842D8 have?
The UC3842D8 has a high-current totem-pole output stage designed to source or sink high-peak current.
- What are some common applications of the UC3842D8?
Common applications include switching regulators, transformer-coupled DC-DC converters, off-line power supplies, and flyback and forward converters.
- How does the undervoltage lockout (UVLO) work in the UC3842D8?
The UVLO ensures that VCC is adequate before enabling the output stage, with turn-on and turn-off thresholds and hysteresis to prevent VCC oscillations.
