Overview
The UC3842ADW is a current-mode PWM controller from Texas Instruments, designed for use in off-line and DC-DC converters. This device is part of the UCx84xA family, known for its high performance and reliability in power supply applications. The UC3842ADW features a low start-up current, trimmed oscillator discharge current, and a robust set of protection mechanisms, including undervoltage lockout and current sense capabilities.
Key Specifications
| Parameter | Min | Typ | Max | Unit |
|---|---|---|---|---|
| Supply Voltage (VCC) | - | - | 30 | V |
| Output Current (IOUT) | - | - | ±1 A | A |
| Output Energy (Capacitive Load) | - | - | 5 µJ | µJ |
| Analog Inputs | -0.3 | - | 6.3 | V |
| Error Amplifier Output Sink Current (ICOMP) | - | - | 10 mA | mA |
| Power Dissipation at TA ≤ 25°C | - | - | 1 W | W |
| Oscillator Frequency (TJ = 25°C) | 47 | 50 | 52 | kHz |
| Maximum Duty Cycle | 94% | 96% | 100% | % |
| Undervoltage Lockout Start Threshold | 14.5 | 16 | 17.5 | V |
| Minimum Operation Voltage After Turn-On | 8.5 | 10 | 11.5 | V |
| Operating Supply Current (VFB = VISENSE = 0 V) | 11 | - | 17 | mA |
Key Features
- Low Start-Up Current: Less than 0.5 mA, making it energy-efficient during startup.
- Trimmed Oscillator Discharge Current: Ensures precise oscillator frequency and reliable maximum duty cycle programming.
- Undervoltage Lockout (UVLO): Protects the device during power-up and power-down sequences, preventing parasitic turn-on of the power MOSFET.
- High-Speed PWM Capability: Can operate at switching frequencies up to 500 kHz.
- Onboard Totem-Pole Gate Driver: Capable of delivering 1 A of peak current.
- Error Amplifier: Can source up to 0.8 mA and sink up to 6 mA, with high open-loop gain and common mode rejection ratio.
- Slope Compensation: Allows for precise operation at high frequencies and duty cycles over 50%.
Applications
- Off-Line and DC-DC Converters: Optimized for use in various power supply configurations, including flyback, forward, and half-bridge converters.
- Isolated and Non-Isolated Power Supplies: Suitable for both isolated and non-isolated power supply designs.
- High-Frequency Switching Applications: Ideal for applications requiring high switching frequencies up to 500 kHz.
Q & A
- What is the typical operating supply current of the UC3842ADW?
The typical operating supply current is around 11 to 17 mA when VFB = VISENSE = 0 V.
- What is the maximum duty cycle for the UC3842ADW?
The maximum duty cycle for the UC3842ADW is between 94% and 100%.
- What is the purpose of the undervoltage lockout (UVLO) feature?
The UVLO feature protects the device during power-up and power-down sequences by preventing the power MOSFET from parasitically turning on due to the Miller effect.
- What is the oscillator frequency range for the UC3842ADW?
The oscillator frequency range is between 47 kHz and 52 kHz at TJ = 25°C.
- Can the UC3842ADW be used in isolated power supply designs?
Yes, the UC3842ADW is suitable for both isolated and non-isolated power supply designs.
- What is the maximum output current capability of the UC3842ADW?
The maximum output current is ±1 A.
- How does the UC3842ADW handle slope compensation?
The device allows for slope compensation by resistively summing a fraction of the oscillator ramp with the current sense signal, enabling precise operation at high frequencies and duty cycles over 50%.
- What is the thermal resistance (RθJA) for the UC3842ADW in the SOIC package?
The thermal resistance (RθJA) for the SOIC package is approximately 77.9 °C/W.
- What is the error amplifier's open-loop gain?
The error amplifier has an open-loop gain of 65 to 90 dB.
- What is the typical start-up current for the UC3842ADW?
The typical start-up current is less than 0.5 mA.
