Tektronix IsoVu TIVM Series, User Manual

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Application examples
In a typical application, a 0.25 Ω resistor might be used to measure a transient
current of 1 A, resulting in a voltage swing of 0.25 V, which can be measured with
the measurement system using a 1X or 5X tip. A typical surface mount resistor
can have a series inductance of less than 0.2 nH and series capacitance of less than
0.04 pF, resulting in much lower impedance at high frequency than could be
obtained with a conventional current probe.
Figure 18: SMT resistor model
Go to http://www.vishay.com/docs/60107/freqresp.pdf for models of different
types of surface mount resistors.
In general, surface mount resistors have fairly low power ratings; care must
be taken not to exceed these ratings when using them as current shunts.
Several vendors make very high power parts that can be used when high
power dissipation is required. For example, the RP0402CB-R500FN-2Q from
Barry Industries (
http://www.barryind.com/ ) is a 1.0 W, 0.5 Ω 0402 resistor
on an AIN substrate, or the RP0402CB-R500FN-2Q from US Microwaves
(
http://www.usmicrowaves.com/ ) is a 1.5 W, 1 Ω resistor on a BeO substrate.
Example 3: ESD troubleshooting
Many devices and systems can be negatively affected by ESD discharges.
Troubleshooting problems that occur during an ESD discharge can be very
dif
fi cult. A piece of test equipment connected to a device undergoing ESD testing
has to not only withstand the ESD discharge, but it also has to reject interference
caused by the rapid changes in potential on the DUT during an ESD discharge test.
For example, consider using the standard human body model of 100 pF and
1500
Ω . If the DUT is being tested to 4 kV and has a capacitance of 50 pF, the
test equipment will be exposed to a voltage change of more than 1 kV in tens
of nanoseconds.
26 TIVM Series Measurement System User Manual