UCC28610
www.ti.com ......................................................................................................................................... SLUS888C–JANUARY 2009–REVISED SEPTEMBER 2009
Avoid HF Ringing
High frequency ringing problems with cascode MOSFET drives can often be avoided. Many converters will not
have this problem because they use an HVMOSFET with a large Vth, large RDS(on), low transconductance gain, or
operate at low current. Ringing problems can also be avoided by minimizing stray inductance. The trace between
the HVMOSFET source and the DRV pin must be kept very short, less than 1 cm. Do not add current probe
loops to the source lead of the HVMOSFET. Do not place ferrite beads on the source lead of the HVMOSFET.
If ringing cannot be avoided, the most efficient and effective methods to solve ringing during switching transients
are:
1. A ferrite chip or bead connected to the gate of the HVMOSFET,
2. A small capacitor connected from DRV to GND and
3. A gate turn-off resistor. These three techniques can be used separately or combined, as shown in Figure 35.
Bulk Voltage
Bulk Voltage
Bulk Voltage
Primary
Primary
Primary
RG-OFF
DG
DG
DG
RG-ON
RG-ON
RG-ON
UCC28610
UCC28610
UCC28610
Ferrite chip
or bead
VGG
DRV
GND
VGG
DRV
GND
VGG
DRV
GND
CDRV
( a )
( b )
( c )
Figure 35. High Frequency Ringing Solutions, (a) ferrite chip, (b) CDRV and (c) RG-OFF
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