The maximum voltage rating for the UC3845DG4 is 30V. However, it's recommended to operate it within 15V to ensure reliable operation and to prevent damage to the internal circuitry.
The frequency of the oscillator in the UC3845DG4 can be calculated using the formula: f = 1.12 / (Rt * Ct), where Rt is the resistance between the RT pin and ground, and Ct is the capacitance between the CT pin and ground.
The soft-start pin (SS) in the UC3845DG4 is used to slowly ramp up the output voltage during startup, reducing the inrush current and preventing damage to the power supply components. It can be connected to a capacitor to ground to set the soft-start time.
To compensate for the voltage drop across the current sense resistor, you can add a voltage offset to the current sense threshold voltage (Vcs) by connecting a resistor divider network between the Vcs pin and the output voltage. The offset voltage should be equal to the voltage drop across the current sense resistor.
The maximum duty cycle of the UC3845DG4 is 99%. However, it's recommended to operate it at a duty cycle of 95% or less to ensure reliable operation and to prevent overheating.
UC3845DG4 datasheet
by Texas Instruments
