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UCC28780: Vgs and Vds oscillate relatively large

Li PengYu
Prodigy 70 points
Part Number: UCC28780

Hello expert:

The main switch tube can realize zero voltage turn-on, as shown in Figure 2. However, when the switch is turned off, Vgs (L) and VDS (L) oscillate relatively large, as shown in Figure 3.

Figure 1

Figure 2

Figure 3

The auxiliary switch tube may not achieve zero voltage turn-on, as shown in Figure 5, which may be the cause of the Vgs(H) oscillation, and the turn-off waveform is normal.

Figure 4

Figure 5

Figure 6

Thank you.

  • +1
    TI__Intellectual 2430 points

    Hi 

    the dead time is fix (40ns) from low side GaN turn off to high side GaN turn on , you can refer the datasheet 7.4.2 section , so the high side GaN may not achieve zero voltage turn-on as your measurement.

    You can use shortest loop to measure the VGS ringing to double check again , and you can refer the app note as below link.

    by the way , you may need to fine tune the resonant capacitance based on your figure1.

    the VDS doesn't keep as Vin+NVo during high side turn on , so resonant cap voltage should be drop , and you can increase the resonant cap or Co1 capacitance.