Analog Devices UG-188 User Manual page 4

UG-188
scope to an ac coupling, 10 mV/division, 2 μs/division time base
and 20 MHz bandwidth.
A standard oscilloscope probe has a long wire ground clip. For
high frequency measurements, this ground clip picks up high
frequency noise and injects it into the measured output ripple.
Figure 3 shows an easy way to measure the output ripple prop-
erly. It requires removing the oscilloscope probe sheath and
wrapping a nonshielded wire around the oscilloscope probe.
By keeping the ground lengths of the oscilloscope probe as
short as possible, true ripple can be measured.
Output Voltage Change
The ADP2119/ADP2120 evaluation board output is preset to
1.2 V; however, the output voltage can be adjusted using the
following equation:
+
⎛
R 4 R 3
= ×
⎜
V 0 6 . V
⎝
OUT
R 4
⎞
⎟
⎠
Rev. 0 | Page 4 of 8
Evaluation Board User Guide
Figure 3. Output Ripple Measurement