Overview
The UC3842AM from Microchip Technology is a high-performance, fixed-frequency, current-mode PWM (Pulse Width Modulation) controller. This integrated circuit is specifically designed for off-line and DC-to-DC converter applications, requiring minimal external components. It features a trimmed oscillator for precise duty cycle control, a temperature-compensated reference, a high-gain error amplifier, and a current sensing comparator. The UC3842AM is part of the UC3842/UC3843/UC3844/UC3845 family, known for their robust and reliable performance in power management systems.
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 |
| Error Amp Output Sink Current | ISINK (E.A) | - | - | 10 | mA |
| Power Dissipation at TA≤25°C (8DIP) | PD | - | - | 1200 | mW |
| Storage Temperature Range | TSTG | -65 | - | +150 | °C |
| 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 | - | - | 0.45 | mA |
| Operating Supply Current | ICC(OPR) | - | - | 17 | mA |
Key Features
- Low Start-Up Current: The UC3842AM has a low start-up current, which is beneficial for power-saving applications.
- Maximum Duty Clamp: It supports a maximum duty cycle of up to 100% for the UC3842 and UC3843 models.
- UVLO With Hysteresis: The device features an under-voltage lockout (UVLO) with hysteresis, ensuring stable operation and preventing false starts.
- Operating Frequency up to 500KHz: The oscillator can operate at frequencies up to 500 KHz, making it versatile for various applications.
- Temperature Compensated Reference: A temperature-compensated reference voltage ensures stable operation over a wide temperature range.
- High Gain Error Amplifier: The high-gain error amplifier provides precise control over the output voltage.
- Current Sensing Comparator: The integrated current sensing comparator allows for accurate current monitoring and control.
- High Current Totem-Pole Output: The output stage is capable of driving power MOSFETs directly.
Applications
The UC3842AM is designed for use in various power management applications, including:
- Off-Line and DC-to-DC Converters: Suitable for both off-line and DC-to-DC converter designs, it is ideal for power supplies, adapters, and other power conversion systems.
- Boost, Buck, Flyback, and Forward Regulators: It can be used in different topologies such as boost, buck, flyback, and forward regulators.
- Isolation Capable Output: The device supports isolation capable output configurations, making it suitable for applications requiring electrical isolation.
- Step-Up and Step-Down Regulators: It is versatile enough to be used in both step-up and step-down regulator designs.
Q & A
- What is the maximum supply voltage for the UC3842AM?
The maximum supply voltage (VCC) for the UC3842AM is 30V.
- What is the typical oscillation frequency of the UC3842AM?
The typical oscillation frequency is around 52 kHz.
- What is the maximum duty cycle for the UC3842AM?
The maximum duty cycle for the UC3842AM is up to 100%.
- What is the start-up current for the UC3842AM?
The start-up current (IST) is typically 0.45 mA.
- What are the UVLO thresholds for the UC3842AM?
The UVLO thresholds for the UC3842AM are 16V (on) and 10V (off) for UC3842 and 8.5V (on) and 7.9V (off) for UC3843.
- What is the power dissipation at TA≤25°C for the 8DIP package?
The power dissipation at TA≤25°C for the 8DIP package is 1200 mW.
- What is the reference output voltage for the UC3842AM?
The reference output voltage (VREF) is typically 5.00 V.
- How does the UC3842AM handle under-voltage lockout?
The device features an under-voltage lockout (UVLO) with hysteresis, which ensures stable operation and prevents false starts by biasing the output driver to a high impedance state during UVLO.
- What are the typical operating supply current and start-up current for the UC3842AM?
The typical operating supply current (ICC(OPR)) is 14 mA, and the start-up current (IST) is typically 0.45 mA.
- What are some common applications of the UC3842AM?
The UC3842AM is commonly used in off-line and DC-to-DC converters, boost, buck, flyback, and forward regulators, as well as in step-up and step-down regulator designs.
