TI recommends a compact layout with the controller, power FETs, and output capacitors placed close together. The input and output stages should be separated to minimize noise coupling. A solid ground plane and a low-impedance power path are also essential. Refer to the TI application note SLUA121 for more details.
The transformer selection depends on the output power, voltage, and current requirements. TI recommends using a transformer with a turns ratio that matches the output voltage and current requirements. The transformer's leakage inductance and magnetizing inductance should also be considered. Refer to the TI application note SLUA122 for transformer selection guidelines.
The maximum duty cycle of the UC2855ADW is typically around 90%. Exceeding this limit can cause output voltage regulation issues. To maintain good regulation, ensure that the duty cycle is kept below 90% by adjusting the input voltage, output voltage, or the transformer turns ratio.
The UC2855ADW has a built-in overcurrent protection feature that can be enabled by connecting a sense resistor to the CS pin. The sense resistor value should be chosen based on the desired overcurrent threshold. When the current exceeds the threshold, the UC2855ADW will shut down and latch off until the fault is cleared.
TI recommends using a low-ESR ceramic or film capacitor with a value of 10uF to 22uF for the input capacitor. The capacitor should be rated for the input voltage and have a low equivalent series resistance (ESR) to minimize voltage ripple and noise.
UC2855ADW datasheet
by Texas Instruments
