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

4.1 OVP1

The VOSNS pin monitors output capacitor voltage via an external resistor divider. An internal comparator (OVP1) monitors the VOSNS pin voltage (VOS). If the voltage on this pin rises above VOvp1Rise, indicating excessive output capacitor voltage, then the controller transitions to its BstOffb state. In this state switching halts to prevent further increase in the output voltage. The controller returns to the Runb state, and resumes switching operation, only after VOS falls below VOvp1Fall, indicating that the output voltage has returned to normal range.

The UCC28056A has 108% VOvp1Rise which is less than the UCC28056B (110%) and UCC28056C (110%). The overshoot performance is better when using the UCC28056A, especially during start-up condition. The waveform in Figure 4-2 shows where the controller enters into OVP1.


GUID-20210924-SS0I-DNDT-BTRM-0RTJC1MWBCPP-low.png

Green: VOSNS, Blue: MOSFET Id
Figure 4-2 UCC28056 Triggers OVP1 Protection