SLUAAH3 October   2021 UCC28056

 

  1.   Trademarks
  2. 1How to Select the Correct Devices Version of UCC28056 Families?
  3. 2How to Complete the Schematic Review of the UCC28056?
    1. 2.1 VOSNS Pin
    2. 2.2 ZCD/CS Pin
    3. 2.3 DRV Pin
    4. 2.4 GND Pin
    5. 2.5 VCC Pin
    6. 2.6 COMP Pin
  4. 3How to Test and Confirm the UCC28056 Working Mode?
    1. 3.1 How to Capture the ZCD/CS Waveform?
    2. 3.2 How to Evaluate UCC28056 Normal Operation Mode Waveform?
  5. 4Protections and how to Identify Them?
    1. 4.1 OVP1
    2. 4.2 OVP2
    3. 4.3 OCP1
    4. 4.4 OCP2
  6. 5Application Debug Frequently Asked Questions (FAQs).
    1. 5.1  How is the UCC28056 GND Pin Connected?
    2. 5.2  There is CCM Inductor Current During Start-Up, is This a Normal Phenomenon?
    3. 5.3  How to Fine-Tune the RC Parameter on the ZCD/CS Pin?
    4. 5.4  Is it Possible to Increase the High Voltage Cap Value on the ZCD Cap Divider?
    5. 5.5  How to Separate the TONMAX Limit or OCP Protection When the PFC Output Voltage Cannot Follow the Regulated Voltage?
    6. 5.6  Does UCC28056 Support DC Input Application?
    7. 5.7  How Does RDG Change the Delay Time for Valley Switching Detection of the MOSFET?
    8. 5.8  Can UCC28056 Meet Harmonic Performance?
    9. 5.9  Does UCC28056 Have Soft Start?
    10. 5.10 Does the UCC28056 Support Auxiliary-Winding PFC Inductor Input on the ZCD Pin?
  7. 6References

5.9 Does UCC28056 Have Soft Start?

There is no soft-start in the UCC28056. Only the COMP pin voltage is pulled down to GND via an internal 5-kΩ resistor to ensure it is discharged before start-up. The time required to boost up the VBUS should therefore depend mainly on the size of the bulk capacitor and the power capability of the PFC stage (PFC inductor value and RCS value) and if there is or is not a load on the output at start up process.