11
KIT8020CRD8FF1217P-1_UM Rev -
User Manual
Use of a ferrite bead (FB) on the gate pin of TO-247 MOSFETs will introduce
high impedance on the gate path for MHz high frequency and reduce the Vgs
ringing.
Reduce the stray capacitance of inductor with single layer structure.
TO-247
TO-247
G
D
S
D
G
S
5ohm
5ohm
1N5819HW
FB
1nF
12ohm
220pF
12ohm
220pF
5ohm
5ohm
FB
1nF
1N5819HW
Figure 8. Gate drive and RC snubber configuration
7.3 Test data
The switching waveforms are shown in the below figures. In the operation of the
synchronous Buck converter, the low-side body diode conducts before low-side
MOSFET is turned on, thus this low-side MOSFET operates in Zero Voltage
Switching (ZVS) mode and high-side MOSFET operates in hard-switching mode.
However, high dv/dt during fast transient of high-side MOSFET will affect the
operational behavior of the low-side MOSFET, and the charge stored in miller
capacitance will be transferred via its gate loop, inducing some spurious gate voltage
in this topology. The above methods mentioned in section 6.2 will help to damp this
noise and reduce the ringing on the gate and drain to source. Note that the incorrect
test method itself may also introduce some noises from oscilloscope measurement,
but it is sometimes not a true representation of the actual transient events on the
switching devices.
