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

2.2 ZCD/CS Pin

An external divider network attached to the ZCD/CS pin transfers both the attenuated drain-to-source voltage (VDS) waveform and the current sense signal (VCS) into the controller. This transfer is possible because the current sense signal requires observation only when the switch is ON and the VDS signal is close to zero. The drain voltage waveform requires sensing only when the switch is OFF and the current sense signal is close to zero. Both the resistor and capacitor dividers on the ZCD/CS pin are necessary. The resistor divider is for Vinac sampling when the controller still does not output pulses to drive the switching device. Add the capacitor divider in parallel with the resistor divider to use high value resistors without introducing filtering and associated phase shift. In this case, ensure that the reactive divider ratio is equal to the resistor divider ratio.

TI recommends starting with a resistor and capacitor divider ratio of 400:1, then fine-tune the capacitor divider following the ZCD/CS Pin section in the UCC28056 6-Pin Single-Phase Transition-Mode PFC Controller datasheet.