UCC25660: UCC25660

HI Tom,

If you are not using the High-Voltage startup, you can simply tie this pin to GND. For this mode of operation, there needs to be another supply for VCCP.

If you are using high-voltage startup, this pin supplies the initial power to the IC, but once it starts switching the auxiliary winding of the transformer will supply power to VCCP. 

Does this answer your question?

HI Tom,

What is the DC supply and where is it coming from?  If you have a supply for VCCP, you can tie the HV to GND.

The EVM users guide s a good example for the feedback network.

I hope this answers your question.

If you are using the EVM, the BLK resistor divider has to be adjusted for the lower input voltage, the EVM was designed assuming a ~380-400V DC input voltage. So for the device to startup with 100VDC, the BLK divider would need be adjusted:

To adjust the BLK resistor divider you can use the excel design calculator to optimize the values. 

For adjusting VOUT, on the EVM, R19 can be used to adjust the output voltage

To really optimize the design you should go through the entire excel calculator to optimize for your input and output requirements. 

I hope this answers your question.