Part Number: UCC28740
Tool/software:
Hello sir.
I am currently using the UCC28740 chip to make a flyback switch power supply load, which is a 24V 0.33A fan. Recently, I found that three consecutive UCC28740 chips are not working. After powering on, I checked that the HV voltage was stable at 344V DC and used trigger mode to capture the VDD pin voltage. I found that the VDD pin was not charged by the Ihv and the voltage remained at 0V. In the specification sheet, I found that the Ihv signal was affected by the fault signal
1.Will this impact be reflected during the first power on and charging.
2. In addition, the charging capacitor 47uF of VDD is connected in parallel with a 100nF capacitor of 0402. Does the specification of 0402 meet the requirements? Alternatively, use the 0603 package
3. May I ask if there is no voltage when the VDD voltage is powered on, and if it can be determined that it is only a problem with the Ihv charging circuit?
4.What are the common factors that cause this problem?
Best Regards
