Overview
The UC3842Q is a high-performance, fixed-frequency, current-mode PWM (Pulse Width Modulator) controller integrated circuit produced by Unitrode, now part of Texas Instruments. This IC is designed to implement off-line or DC-to-DC fixed-frequency current-mode control. It features an undervoltage lockout (UVLO) with a start-up current of less than 1 mA and a precision reference voltage. The UC3842Q is optimized for efficient power sequencing of off-line converters, DC-to-DC regulators, and for driving power MOSFETs or transistors.
Key Specifications
| Parameter | Test Conditions | Min | Typ | Max | Unit |
|---|---|---|---|---|---|
| Reference Output Voltage | IO = 1.0 mA, TJ = 25°C | 4.9 | 5.0 | 5.1 | V |
| Line Regulation | VCC = 12 V to 25 V | -2.0 | - | 20 | mV |
| Load Regulation | IO = 1.0 mA to 20 mA | -3.0 | - | 25 | mV |
| Temperature Stability | - | -0.2 | - | - | mV/°C |
| Output Noise Voltage | f = 10 Hz to 10 kHz, TJ = 25°C | - | - | 50 | µV |
| Short-Circuit Output Current | - | -30 | -100 | -180 | mA |
| Oscillator Frequency | TJ = 25°C, RT = 10 kΩ, CT = 3.3 nF | 47 | 50 | 52 | kHz |
| High-Level Output Voltage | IOH = -20 mA | 12 | 13.5 | - | V |
| Low-Level Output Voltage | IOL = 20 mA | 0.1 | 0.4 | - | V |
| Rise Time | CL = 1 nF, TJ = 25°C | 50 | 150 | - | ns |
| Fall Time | CL = 1 nF, TJ = 25°C | 50 | 150 | - | ns |
Key Features
- Undervoltage Lockout (UVLO): Features a start-up current of less than 1 mA and precision reference voltage.
- Pulse-Width Modulation (PWM): Includes a PWM comparator for current-limit control and a totem-pole output stage to source or sink high-peak current.
- Internal Oscillator: Uses an external capacitor and resistor to set the switching frequency, which can also be used for Constant-On Time or Constant-Off Time controllers.
- Current Sense Input: Configured for external current-to-voltage conversion with a ground-referenced resistor.
- High-Performance Output Stage: Designed to drive N-channel MOSFETs with low output voltage in the off state.
- Temperature Range: Operates between 0°C and 70°C.
Applications
- Off-Line Converters: Efficient power sequencing for off-line converters.
- DC-to-DC Regulators: Optimized for use in DC-to-DC regulators.
- Power MOSFETs/Transistors: Designed for driving power MOSFETs or transistors.
- Current Mode Control: Provides all the performance advantages of current mode operation in power supply designs.
Q & A
- What is the primary function of the UC3842Q?
The UC3842Q is a fixed-frequency, current-mode PWM controller used for implementing off-line or DC-to-DC converters.
- What is the operating temperature range of the UC3842Q?
The UC3842Q operates between 0°C and 70°C.
- What is the purpose of the undervoltage lockout (UVLO) in the UC3842Q?
The UVLO ensures the IC starts up only when the input voltage is above a certain threshold and maintains operation above a minimum voltage after start-up.
- How is the oscillator frequency set in the UC3842Q?
The oscillator frequency is set using an external resistor (RT) and capacitor (CT), with the charging time given by Tcharge = RT · CT.
- What type of output stage does the UC3842Q have?
The UC3842Q has a totem-pole output stage designed to source or sink high-peak current, suitable for driving N-channel MOSFETs.
- What is the typical reference output voltage of the UC3842Q?
The typical reference output voltage is 5.0 V.
- How does the current sense input work in the UC3842Q?
The current sense input is configured for external current-to-voltage conversion using a ground-referenced resistor.
- What are some common applications of the UC3842Q?
Common applications include off-line converters, DC-to-DC regulators, and driving power MOSFETs or transistors.
- What is the significance of the power supply rejection ratio (PSRR) in the UC3842Q?
The PSRR indicates the IC's ability to reject power supply noise, with a typical value of -70 dB.
- How does the UC3842Q handle short-circuit conditions?
The UC3842Q has a short-circuit output current protection with values ranging from -30 mA to -180 mA.
