Overview
The UC3842J is a current-mode PWM (Pulse Width Modulator) controller integrated circuit produced by Unitrode, now part of Texas Instruments. This IC is designed to provide efficient and cost-effective solutions for power supply design, particularly in DC-DC converters and off-line power supplies. It is optimized for good electrical performance and low cost, making it a versatile component in various power management applications.
Key Specifications
| Parameter | Value | Unit |
|---|---|---|
| VCC (Low impedance source) | 30 | V |
| VFB and VISENSE (Analog input voltage) | -0.3 to 6.3 | V |
| VCC (Input Voltage, Q and D Package only) | 30 | V |
| IOUTPUT (Output drive current) | ±1 | A |
| ICOMP (Error amplifier output sink current) | 10 | mA |
| EOUTPUT (Output energy, capacitive load) | 5 | µJ |
| TJ (Junction temperature) | 150 | °C |
| Tstg (Storage temperature) | -65 to 150 | °C |
| IOUTPUT (Average output current) | 200 | mA |
| IVREF (Reference output current) | -20 | mA |
| fOSC (Oscillator frequency) | 100 to 500 | kHz |
| TA (Operating free-air temperature) | 0 to 70 | °C |
Key Features
- Current-Mode Operation: Provides all the performance advantages of current-mode operation, including improved line and load regulation and easier implementation of overcurrent protection.
- Low Cost: Designed to be cost-effective, using only two magnetic elements and an inexpensive control circuit.
- Under-Voltage Lockout (UVLO): Ensures that VCC is adequate before enabling the output stage, with fixed turn-on and turn-off thresholds and a 6V hysteresis to prevent VCC oscillations.
- Oscillator Programmability: Allows the oscillator frequency to be set using external timing resistor (RT) and capacitor (CT), with a maximum frequency of 500 kHz.
- Maximum Duty Cycle Control: The UC3842 and UC3843 have a maximum duty cycle of approximately 100%, while the UC3844 and UC3845 are clamped to 50% maximum duty cycle.
- Current Sensing and Limiting: External current-to-voltage conversion with ground-referenced resistor Rs, and internal clamping to prevent excessive current.
- Error Amplifier Compensation: Allows for external compensation to control the converter’s closed-loop frequency response.
- Totem-Pole Output: Single totem-pole output stage suitable for driving power MOSFETs or transistors.
Applications
- DC-DC Converters: Suitable for various DC-DC converter topologies, including boost, buck, and flyback converters.
- Off-Line Power Supplies: Optimized for efficient power sequencing of off-line converters.
- Power MOSFET and Transistor Drivers: Designed to drive power MOSFETs or transistors in high-current applications.
- Industrial and Consumer Electronics: Used in a wide range of industrial and consumer electronic devices requiring efficient power management.
Q & A
- What is the UC3842J used for? The UC3842J is a current-mode PWM controller used in DC-DC converters, off-line power supplies, and other power management applications.
- What are the key features of the UC3842J? Key features include current-mode operation, low cost, under-voltage lockout, oscillator programmability, and totem-pole output.
- What is the maximum oscillator frequency of the UC3842J? The maximum oscillator frequency is 500 kHz.
- How does the UC3842J handle current sensing and limiting? It uses external current-to-voltage conversion with a ground-referenced resistor Rs and internal clamping to prevent excessive current.
- What is the purpose of the error amplifier in the UC3842J? The error amplifier allows for external compensation to control the converter’s closed-loop frequency response.
- What are the operating temperature ranges for the UC3842J? The operating free-air temperature range is from 0°C to 70°C.
- Can the UC3842J be used in safety-critical applications? It is important to consult the datasheet and relevant safety guidelines before using the UC3842J in safety-critical applications.
- How does the UC3842J ensure VCC is adequate before enabling the output stage? It uses an under-voltage lockout (UVLO) circuit with fixed turn-on and turn-off thresholds and a 6V hysteresis.
- What types of converters can the UC3842J be used in? It can be used in boost, buck, and flyback converters, among others.
- What is the maximum duty cycle for the UC3842J? The UC3842 and UC3843 have a maximum duty cycle of approximately 100%, while the UC3844 and UC3845 are clamped to 50% maximum duty cycle.
