PDN Probes
15
2-Port Probe Applications
Regulator Load Step Testing
(VRTS3 Board)
The 2-port probe can be used to transmit a load current step through one port, while
measuring the response from the other port, simultaneously. This is a great advantage when
browsing your board’s power rails, looking for problems and poor stability. All you have to
do is setup the load step range and then simply move the probe to the capacitor at the
output of each regulator IC in order to view the transient response.
In this example of a linear regulator load step test, the J2150A Harmonic comb is used as a
simple and portable square wave generator (one of its modes of operation). It drives the
Picotest J2111A current injector. This modulates the load current at the output of the
regulator when the probe is applied. The P2130A DC blocker may be needed so that the
scope does not load the output of the regulator.
The impedance and step load are measured in the same way. Load step testing does not get
any easier.
Figure 9: The step load response is shown on CH1 and the applied load step is shown on
CH3. The amount of ringing is related to the stability of the system.