The maximum voltage rating for the UC3845AN is 30V, but it's recommended to operate it within 15V to ensure reliable operation and to prevent damage to the internal circuitry.
The values of CT and RT determine the oscillator frequency. A good starting point is to use the values recommended in the datasheet (CT = 3.3nF and RT = 10kΩ). Then, adjust them based on your specific application requirements and the desired switching frequency.
The soft-start pin (SS) is used to gradually increase the output voltage during startup, reducing inrush currents and electromagnetic interference (EMI). Connect a capacitor (typically 10nF to 100nF) from the SS pin to ground, and a resistor (typically 1kΩ to 10kΩ) from the SS pin to the output voltage. This creates a ramp-up voltage that controls the output voltage during startup.
To ensure stable operation, make sure to decouple the power supply pins (VCC and GND) with a 10uF to 100uF capacitor, and use a low-ESR capacitor for the output filter. Also, keep the layout clean and minimize parasitic inductances and capacitances. Additionally, use a snubber network (e.g., R-C-R) across the output switch to prevent oscillations.
The UC3845AN is a controller IC and does not have an output stage, so it does not have a maximum output current capability. The output current is determined by the external power switch (e.g., MOSFET or BJT) and the design of the power stage.
UC3845AN datasheet
by STMicroelectronics
