Wolfspeed SpeedVal MOD-MB-3P-0900V-40A Series User Manual page 63

Distorted gate waveforms seen on oscilloscope
On occasion, V or gate waveforms may appear distorted (Figure 55). There are several connections in the gate
GS
measurement path. If one is not solidly connected, it may result in distorted gate waveforms. Check the
following:
 x10 oscilloscope probe tip to BNC coupling

Probe BNC coupling to 6" BNC to MMCX adapter.
 6" MMCX adapter to power daughter card MMCX test point
Measuring high voltage on the control side of the board or getting an overvoltage warning from the
function generator.
The return (negative) terminal of the 12 V power to the motherboard must be tied to earth ground. The voltage
sensing circuits present on the motherboard provide a leakage path between the high voltage bus and the low-
voltage control circuits. When a grounded high-voltage power supply or grounded oscilloscope probe is used
for measuring on the high-voltage side of the system, it completes the leakage path circuit. The high impedance
of these sense circuits results in less than 1mA of leakage current; however, in an ungrounded system, this can
cause the control side of the motherboard to float up in voltage relative to earth ground. By connecting the
negative rail of the 12V input to earth ground, the potential of the control circuit will remain referenced to
ground.
PRD-08611 REV. 1, June 2024
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the Wolfspeed logo are trademarks of Wolfspeed, Inc. Other trademarks, product and company names are the property of their
respective owners and do not imply specific product and/or vendor endorsement, sponsorship or association.
V
GS
Figure 55: Distorted V
MOD-MB-3P-0900V-40A SpeedVal™ Kit Three-Phase Motherboard User Guide
Waveform
GS
63