What Is UC3843AN PWM Controller IC?

What Is UC3843AN?
- The UC3843AN is a high-performance, fixed-frequency PWM controller IC
- The UC3843AN is primarily used for switching power supplies and DC-DC converters.
- It operates in a current-mode control configuration, allowing for improved response time and precise control over the output voltage and current.
- This IC features a precision-trimmed oscillator for precise duty cycle control, a temperature-compensated reference, a high-gain error amplifier, a current-sensing comparator, and a high-current totem pole output
- The UC3843AN includes protective features like undervoltage lockouts with hysteresis, cycle-by-cycle current limiting, programmable output deadtime, and a latch for single pulse metering.
Pinout of UC3843AN
Compensation: Error amplifier compensation.
Voltage Feedback (VFB): Output voltage feedback.
Current Sense: Current sensing for cycle-by-cycle current limiting.
RT/CT: Timing resistor and capacitor to set oscillation frequency.
Ground (GND): Ground connection.
Output: Drives the power MOSFET.
Vcc: Power input.
Vref: 5V precision reference voltage output.
Circuit of UC3843AN
The UC3843AN achieves voltage regulation through its internal error amplifier, oscillator, PWM comparator, and power MOSFET driver output modules. During operation, the feedback voltage (VFB) is sampled from the output and sent to pin 2, where the error amplifier compares it to an internal reference voltage, thereby stabilizing the output voltage.
In terms of current flow, the UC3843AN performs current sensing through pin 3, where the sensed current signal is compared with the error amplifier’s output. When the sensed current exceeds a set threshold, the PWM output signal shuts off, limiting the current through the power device, thus providing cycle-by-cycle current limiting protection.
Pin 4, the oscillator control pin, sets the operating frequency via an external resistor and capacitor, enabling precise synchronization of the PWM control signal. Additionally, the built-in Undervoltage Lockout (UVLO) function shuts down the output when the input voltage is too low, ensuring the safety of the entire circuit.
Specification of UC3843AN
Voltage - Supply (Vcc/Vdd): 8.4V ~ 30V
Reference Voltage (Vref): 5V ± 0.5%
Output Voltage Range: 5V
Oscillator Frequency: Up to 500 kHz
Duty Cycle (Max): 96%
Output Current: 1A peak
Current Sense Threshold: 1V
Quiescent Current: 17 mA
Operating Temperature: 0°C ~ 70°C
Package: 8-PDIP
Features of UC3843AN
Optimized for Off-Line and DC-DC Converters
Low Start-Up Current (< 0.5mA)
Trimmed Oscillator Discharge Current
Automatic Feedforward Compensation
Pulse-by-Pulse Current Limiting
Enhanced Load Response Characteristics
Undervoltage Lockout With Hysteresis
Double Pulse Suppression
High-Current Totem Pole Output
Internally-Trimmed Bandgap Reference
Up to 500kHz Operation
Applications of UC3843AN
Switch Mode Power Supplies (SMPS)
DC-DC Converters
Power Modules
Industrial PSU
Battery Operated PSU
Package of UC3843AN
The package type of the UC3843AN is 8-PDIP (dual in-line package), which is a standard 8-pin in-line plastic package. This package form is easy to mount on a printed circuit board (PCB) and is suitable for use in a wide range of off-line power supply and DC-DC converter applications.
Where to Use UC3843AN?
The UC3843AN is widely used in offline and DC-DC conversion circuits. In addition, the UC3843AN's current-mode control capability and stabilized frequency make it ideal for use in switched-mode power supplies (SMPS).
Another important use case for the UC3843AN is in industrial power systems, where the UC3843AN integrates features such as UVLO, current limiting, and programmable output dead time. The device's totem pole output stage efficiently drives power MOSFETs and can handle high current loads. As a result, the UC3843AN is commonly used in telecom equipment, consumer electronics, and other environments that require reliable DC power conversion.
How to Test UC3843AN?
First, prepare the testing environment. Place the UC3843AN on a test circuit board and connect an appropriate power supply, typically a 7-12V DC source. Next, attach an oscilloscope probe to the output pin to monitor the PWM output waveform. Additionally, connect a current probe to pin 3 to measure the current sense signal. Then, connect suitable resistor and capacitor components to the RT/CT pin to set the oscillation frequency. Power on the circuit, and observe the output waveform. If a stable PWM waveform appears, it indicates that the oscillator and output modules are functioning properly.
Next, check the UVLO and overcurrent protection features. Gradually reduce the input voltage; when it drops to around 7.6V, the output should automatically shut off, confirming that the UVLO feature is working. To test overcurrent protection, connect a variable load to the output, slowly increase the load current, and observe. When the current exceeds the threshold, the output waveform should disappear or be limited, indicating that overcurrent protection has been activated. After completing all tests, power off the circuit and record the results.
FAQs
What is the difference between UC3842A and UC3843A?
The primary difference is the undervoltage lockout (UVLO) thresholds. The UC3842A has UVLO thresholds of 16V (on) and 10V (off), which suit it for off-line converters. The UC3843A, however, has lower UVLO thresholds of 8.5V (on) and 7.6V (off), making it more suitable for low-voltage applications.
What protective features does the UC3843AN include?
It includes several protective features: undervoltage lockout (UVLO) to prevent operation at low input voltages, cycle-by-cycle current limiting to protect against overcurrent conditions, programmable output deadtime, and a latch for single-pulse metering.
How does UC3843AN provide overcurrent protection?
Overcurrent protection is achieved through the current sense pin, which monitors the current flowing through the load. When the sensed current exceeds a certain threshold, the PWM output is shut off on a cycle-by-cycle basis, preventing excessive current from damaging the components.