UC3842AD datasheet by Texas Instruments

UC3842AD Frequently Asked Questions (FAQs)

• What is the recommended operating voltage range for UC3842AD?
  The recommended operating voltage range for UC3842AD is 12V to 28V, with a maximum rating of 30V.
• How do I choose the right resistor values for the oscillator circuit?
  The oscillator circuit resistor values (Rt and Ct) can be calculated using the formulae provided in the datasheet. A general guideline is to choose Rt = 10kΩ to 100kΩ and Ct = 3.3nF to 10nF for a frequency range of 10kHz to 100kHz.
• What is the purpose of the soft-start pin (SS) and how do I use it?
  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 SS to GND, and a resistor (typically 1kΩ to 10kΩ) from SS to VCC.
• How do I compensate for the voltage drop across the current sense resistor (Rcs)?
  The voltage drop across Rcs can be compensated by adding a voltage offset to the current sense input (CS) pin. The offset voltage can be calculated using the formula: Voffset = (Rcs x Iout) / (R1 + R2), where R1 and R2 are the resistors in the voltage divider network.
• What is the maximum allowable current through the output switch (Q1) and how do I limit it?
  The maximum allowable current through Q1 is 1.5A. To limit the current, use a current sense resistor (Rcs) and set the current limit threshold (Ilim) using the formula: Ilim = 0.5V / Rcs. Choose Rcs to limit the current to the desired value.