UCC28740: UCC28740 MOSFET G Waveform anomalies, why does this happen?

User,

Thanks for the interest in TI here.

This signal is the gate of the MOSFET?

Can you show what the DRV output is directly from the controller?

I can't see the vertical scale but it looks like the Miller region of the MOSFET. You might confirm that by comparing to the MOSFET datasheet for Gate voltage during turn on and seeing the DRV pin signal of the ucc28740.

Regards

John

hi john,

Thank you for answering my question。

1，yes the signal is the gate of  the mosfet.

2，I Short circuit the resistance R63,the signal is the same

3,the vertical scale 5V/DIV，I think the platform of the signal is caused by  Miller capacitance，this mosfet STF18NM80 max Gate threshold voltage is 5V ,the Qgd is 40nc when VDD = 640 V, ID = 17 A VGS = 10 V

the max frequency of the flyback is 65KHZ。

the ucc28740 Functional Block Diagram is:

the DRV Feature Description (continued) is:

the ucc28740 in a valley-skipping mode,the Vdrv is:

I bought some AOTF15S65L,the Electrical Characteristics is:

the max VGS(th) is  4V, the Qgd is 5.6nc when VGS=10V, VDS=480V, ID=7.5A;I'll show the details when I compare the results of these two MOSFET tests.

best Regards.

yu.

hi john,

Input:   AC 220V

output: 24VDC    2.4A

the mosfet is AOTF15S65L