UCC28610: UCC28610 zcd delay

Hello ,

I cannot open your attachments.  However, the UCC28610 after it sees zero volts on the ZCD will wait tdly(zcd) of a 150 ns before turning on the gate drive and they may refereeing to a portion of the resonant ring period.

Please refer to figure 35 in the data sheet.  The Aux winding signal should is transformer coupled to the switch node through the auxiliary to primary  (Na/Np) turns ratio. So if figure 23 think of VDS as VZCD and VBULK(min) as ground.

After the flyback converter has delivered energy to the secondary at the end of tDM.  The switch node will LC tank with energy that is left in the transformer's magnetizing inductance (Lm) and the switch node capacitance.  When VDS has rung to Vbulk(min) and Vaux/VZCD will cross zero volts 1/4 the period of the ring frequency will occur.  If this period was 250 ns your gate drive would turn on 250 ns + 150 ns = 400 ns.

This 150 ns delay ensures the gate drive turns on while switch node is ringing below Vbulk(min) for near valley switching.

Regards,