Texas Instruments recommends a 4-layer PCB with a solid ground plane, and to keep the switching node (pin 3) away from sensitive analog circuits. A good layout practice is to keep the high-frequency components (e.g., the transformer, diodes, and capacitors) close to the IC, and to use a shielded inductor or a toroidal inductor to reduce radiated emissions.
The transformer should be designed to meet the required output power, voltage, and current. The primary inductance should be chosen based on the minimum operating frequency and the maximum duty cycle. A good starting point is to use a transformer with a primary inductance of 10-20 μH and a turns ratio of 1:1 to 1:2.5. The transformer's leakage inductance should be minimized to reduce EMI.
The maximum allowed voltage on the VCC pin is 18V. Exceeding this voltage may damage the internal voltage regulator and other components. It's recommended to use a voltage regulator or a zener diode to regulate the input voltage to the UC3856DWG4.
The UC3856DWG4 has an internal oscillator, but it can be synchronized with an external clock signal through the RT/CT pin. The external clock signal should be a square wave with a frequency between 100 kHz and 500 kHz. The clock pin is sensitive to noise, so it's recommended to use a low-impedance source and to keep the clock signal away from noisy circuits.
The recommended operating temperature range for the UC3856DWG4 is -40°C to 85°C. Operating the device outside this range may affect its performance, reliability, and lifespan.
UC3856DWG4 datasheet
by Texas Instruments
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