Overview
The UC3842ADTR, produced by Texas Instruments, is a current-mode PWM (Pulse Width Modulator) controller integrated circuit. This IC is designed to provide low-cost current-mode control for various power supply applications, including off-line converters and DC to DC regulators. It is part of the UC3842 family, which includes the UC3842, UC3843, UC3844, and UC3845, each with slightly different features but sharing many common characteristics.
The UC3842ADTR is optimized for efficient power sequencing and can drive power MOSFETs or bipolar transistors. It features a two-loop current-mode control system, which allows for precise control over the peak inductor current, ensuring good electrical performance at a low cost.
Key Specifications
| Parameter | Symbol | Min. | Typ. | Max. | Unit |
|---|---|---|---|---|---|
| Supply Voltage | VCC | - | - | 30 | V |
| Output Current | IO | - | - | ±1 | A |
| Analog Inputs (Pin 2, 3) | V(ANA) | -0.3 | - | 6.3 | V |
| Reference Output Voltage | VREF | 4.90 | 5.00 | 5.10 | V |
| Oscillation Frequency | f | 47 | 52 | 57 | kHz |
| Maximum Duty Cycle | D(MAX) | 95 | 97 | 100 | % |
| Start-Up Current | IST | - | - | 1 | mA |
| Operating Supply Current | ICC(OPR) | - | 14 | 17 | mA |
| Storage Temperature Range | TSTG | -65 | - | +150 | °C |
Key Features
- Current-Mode Control: The UC3842ADTR operates in current-mode, allowing for precise control over the peak inductor current, which is beneficial for achieving good electrical performance and stability in power supplies.
- Low-Cost Design: This IC is designed to be cost-effective while providing the performance advantages of current-mode operation.
- Under-Voltage Lockout (UVLO): The IC includes UVLO circuitry that ensures the VCC is adequate before enabling the output stage, preventing VCC oscillations during power sequencing.
- Programmable Oscillator: The oscillator frequency can be programmed using external timing resistor (RT) and timing capacitor (CT), allowing for flexible design configurations.
- High Maximum Duty Cycle: The UC3842ADTR has a maximum duty cycle of approximately 100%, making it suitable for a wide range of applications.
- Error Amplifier: The IC includes an error amplifier with an output available for external compensation, allowing users to control the converter’s closed-loop frequency response.
- Current Sensing and Limiting: The IC features current sensing and limiting capabilities, which can be configured using external components to control the peak current.
Applications
- Off-Line Converters: The UC3842ADTR is optimized for efficient power sequencing in off-line converters.
- DC to DC Regulators: It is suitable for use in DC to DC regulators, providing stable and efficient power conversion.
- Power MOSFET and Bipolar Transistor Drivers: The IC can drive power MOSFETs or bipolar transistors, making it versatile for various power supply designs.
- Flyback and Forward Converters: The UC3842ADTR is particularly advantageous in flyback and forward converter applications due to its duty cycle clamp feature.
Q & A
- What is the primary function of the UC3842ADTR?
The UC3842ADTR is a current-mode PWM controller designed for use in power supply applications, including off-line converters and DC to DC regulators.
- What is the maximum supply voltage for the UC3842ADTR?
The maximum supply voltage (VCC) for the UC3842ADTR is 30V.
- How is the oscillator frequency programmed in the UC3842ADTR?
The oscillator frequency is programmed using external timing resistor (RT) and timing capacitor (CT), with the formula Fosc (kHz) = 1.72 / (RT (k) × CT (pf)).
- What is the maximum duty cycle of the UC3842ADTR?
The UC3842ADTR has a maximum duty cycle of approximately 100%.
- What is the purpose of the Under-Voltage Lockout (UVLO) feature?
The UVLO feature ensures that the VCC is adequate before enabling the output stage, preventing VCC oscillations during power sequencing.
- How does the current sensing and limiting work in the UC3842ADTR?
Current sensing is done externally with a ground-referenced resistor Rs, and current limiting occurs when the voltage at the current sense input reaches a threshold value.
- What is the role of the error amplifier in the UC3842ADTR?
The error amplifier allows for external compensation, enabling users to control the converter’s closed-loop frequency response.
- What are the typical applications of the UC3842ADTR?
The UC3842ADTR is typically used in off-line converters, DC to DC regulators, and for driving power MOSFETs or bipolar transistors.
- What is the storage temperature range for the UC3842ADTR?
The storage temperature range for the UC3842ADTR is -65°C to +150°C.
- What is the operating supply current of the UC3842ADTR?
The operating supply current (ICC(OPR)) of the UC3842ADTR is typically 14 to 17 mA.
