Overview
The UC3843ADX is a fixed frequency current-mode PWM (Pulse Width Modulation) controller designed by Fairchild Semiconductor. It is specifically tailored for offline and DC to DC converter applications, requiring minimal external components. This controller integrates various essential circuits, including under-voltage lockout (UVLO), low startup current circuit, temperature-compensated reference, high gain error amplifier, current sensing comparator, and a high current totem-pole output for driving a power MOSFET.
Key Specifications
| Parameter | Symbol | Value | Unit |
|---|---|---|---|
| Supply Voltage | VCC | 30 | V |
| Output Current | IO | ±1 | A |
| Analog Inputs (Pin 2, 3) | VI(ANA) | -0.3 to 6.3 | V |
| Error Amp Output Sink Current | ISINK(EA) | 10 | mA |
| Power Dissipation at TA≤25°C (8DIP) | PD | 1200 | mW |
| Reference Output Voltage | VREF | 4.90 - 5.10 | V |
| Oscillation Frequency | f | 47 - 57 kHz | kHz |
| UVLO Start Threshold (UC3843A) | VTH | 7.8 - 9.0 V | V |
| UVLO Minimum Operating Voltage (UC3843A) | VTL | 7.0 - 8.2 V | V |
| Maximum Duty Cycle | DMAX | 94 - 100% | % |
| Start-Up Current | IST | 0.2 - 0.4 mA | mA |
Key Features
- Low startup current below 0.3 mA
- Operating frequency up to 500 kHz
- Under-voltage lockout (UVLO) with hysteresis
- Short shutdown delay time (typ. 100 ns)
- High current totem-pole output for driving a power MOSFET
- Output swing limiting (22 V)
- Cycle-by-cycle current limiting
- Temperature-compensated reference
- High gain error amplifier
- Current sensing comparator
Applications
The UC3843ADX is designed for use in offline and DC to DC converter applications. It is particularly suitable for power supply designs that require high efficiency, reliability, and minimal external components. Common applications include:
- Switch-mode power supplies
- DC to DC converters
- Offline power supplies
- High-frequency power conversion systems
Q & A
- What is the primary function of the UC3843ADX?
The UC3843ADX is a fixed frequency current-mode PWM controller designed for offline and DC to DC converter applications.
- What is the typical startup current of the UC3843ADX?
The typical startup current is below 0.3 mA.
- What is the maximum operating frequency of the UC3843ADX?
The maximum operating frequency is up to 500 kHz.
- What is the UVLO threshold for the UC3843A?
The UVLO start threshold for the UC3843A is between 7.8 V and 9.0 V, and the minimum operating voltage is between 7.0 V and 8.2 V.
- What is the maximum duty cycle of the UC3843ADX?
The maximum duty cycle is between 94% and 100%.
- What type of output does the UC3843ADX have?
The UC3843ADX has a high current totem-pole output for driving a power MOSFET.
- What is the output swing limiting voltage of the UC3843ADX?
The output swing limiting voltage is 22 V.
- Does the UC3843ADX have cycle-by-cycle current limiting?
Yes, the UC3843ADX features cycle-by-cycle current limiting.
- What is the typical shutdown delay time of the UC3843ADX?
The typical shutdown delay time is 100 ns.
- What are common applications for the UC3843ADX?
Common applications include switch-mode power supplies, DC to DC converters, offline power supplies, and high-frequency power conversion systems.
