UCC256404: UCC256404

Hi Stuart,

You can refer the following figure for the resonant capacitor valley voltage when the converter is operating at resonance:

Following two figures shows the resonant capacitor voltage at below and above resonance. we can observe that capacitor peak to peak voltage changes with the operating frequency.

Please let me know if you have any further questions.

Regards

Manikanta P

Hi Stuart,

ISNS voltage is mainly used for current protection and for current polarity detection during switching to the avoid the ZCS region.

For understanding kISNS and VISNS peak, you need to understand about the OCP1,OCP2,OCP3 protections.

OCP1,OCP2, OCP3 protections:

OCP1 will trip after 4 consecutive switching cycles where ISNS is greater than the OCP1 trip threshold of 4V typical. OCP2 looks at the average of the ISNS signal where the input going into the averaging block is ISNS when the high side gate is on and 0V when the high side gate is off. The amount of time this averaged ISNS voltage must stay above the OCP2 threshold is 2ms typical. OCP3 functions in a similar way to OCP2 in that it also looks at the averaged ISNS voltage. The averaged ISNS voltage must stay above the OCP3 threshold for 50ms in order for OCP3 to trip.

OCP1 is primarily used to react to a short circuit event and shut down quickly. OCP2 and OCP3 are similar to an overload protection that have a slower reaction time. The response to OCP1, OCP2 and OCP3 are the same. The controller will stop switching for 1s. After 1s, the controller will attempt to soft start.

I have gone through ISNS sensing calculations in the attached document. This should give pretty good insight about kisns and Visnspeak.

New Microsoft Word Document (5).pdf

Please let me know if you have further questions.

Regards

Manikanta P