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

4.4 OCP2

A second comparator (OCP2) with a higher threshold, and shorter blanking time, also monitors the current sense voltage signal. If triggered, this second OCP2 comparator also terminates the current on-time (TON) duration early. In addition, if the controller triggers the OCP2 comparator on three consecutive switching cycles, it also triggers a long fault. The long fault halts switching operation and prevents restart for a period of TLongFlt.

The ZCD/CS blanking time from DRV rising edge to Enable OCP2 Comparator Output is 250 ns. The waveform in Figure 4-5 shows where the controller enters into OCP2.


GUID-20210924-SS0I-FF9B-PKVZ-MTZZZW2W75QF-low.png

Dark Blue: ZCD/CS; Light Blue: DRV
Figure 4-5 UCC28056 Triggers OCP2 Protection

The resistor between the controller DRV pin and MOSFET gate pin influences the turning on and off speed of the MOSFET. A higher value resistor can lower the turning on speed of the MOSFET and also helps on EMC performance. If the resistor value is too high, it may delay the VDS falling edge; therefore causing a delay on the ZCD/CS pin. If 250-ns blanking time is not enough for ZCD/CS falling down to correctly sampling current through the MOSFET, there may be a mis-triggering of OCP2.