Tektronix IsoVu TIVM Series, Руководство пользователя

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Application examples
In general there are three characteristic regions of interest of the turn-on waveform
(See Figure 16.):
The fi rst region is the C
GS
charge time.
The second region is the Miller Plateau (the time required to charge the
gate-drain Miller capacitance (C
GD
), and is V
DS
dependent. The charge time
increases as V
DS
increases.
The third region occurs when the channel is in conduction and the gate
charges up to its
fi nal value.
Due to the rapid rise of the voltage on the switch node during the high side
turn-on, there can be very high frequency and high amplitude common mode
voltage changes during the transition. If this common mode voltage transient is
not rejected, then the measurement of the high-side V
GS
during the transition is
not possible.
Example 2: High-side drain current measurement
Current sensing is a critical measurement in many applications. Using the half
bridge circuit again as an example, measuring the high-side drain current, I
D
, can
be very challenging particularly during startup. At startup, there can be common
mode voltage transients due to parasitic inductance in the supply leads in addition
to large current swings. Inserting a conventional current probe into the circuit at
this point would require adding excessive inductance, which might limit circuit
performance. Using a small value resistor as a current shunt makes it possible
to take very high frequency current measurements with minimal additional
impedance in the drain connection. (See Figure 17.)
Figure 17: High side current shunt
TIVM Series Measurement System User Manual 25