XT2640 Operating Manual
13 July 2016
Page 81 of 187
The FUND setting of the DC VPA should be set to the VPA measuring the PWM Generator.
The HARMONICS setting for the DC VPA should be set to 0 (it can also be set to a non‐zero value, in which case the
ripple content of the DC supply will be available as harmonics).
Use the same LF/PERIOD and RESPONSE settings in both VPAs.
In this manner the two VPA measurements will be closely synchronized by always starting them at the same time so
efficiency will track fast changes to signals. Both measurement periods will be almost the same, so synchronization will be
very close and measurements will be almost continuous as any pauses between measurements will be very short (typically
a few tens of µsec).
3.
If there will be significant changes to the levels or signals which require tracking for efficiency results and the supply is
either DC containing ripple at some frequency other than the modulation frequency, or it is an AC supply (e.g. mains).
The MEAS MODE should be set to SYNC VPA.
Both sets of measurements should be configured in separate VPAs. Any VPA can be used for either measurement and
both are independently configured. It is recommended that, if possible, both LF/PERIOD settings be the same value.
Use the same RESPONSE setting in both VPAs.
In this manner the two VPA measurements will be closely synchronized by always starting them at the same time, even
though they might not actually end at exactly the same time, so efficiency will track fast changes to signals as much as
possible but there may be a slight difference between the two measurement periods and neither measurement will be
continuous as each must wait for the other to finish before it can restart.
4.
If none of the above situations are true, or if you are uncertain if any of the above situations are true.
The MEAS MODE should be set to MULTI VPA.
Both sets of measurements should be configured in separate VPAs. Any VPA can be used for either measurement and
both are completely independently configured.
Although the two measurement periods will be asynchronous you can reduce any abnormal efficiency results during
fast changes as follows –
o
Use the same LF/PERIOD setting in both VPAs if possible.
o
Use the shortest possible measurement period in the LF/PERIOD settings of both VPAs.
o
Use the same RESPONSE setting in both VPAs.
In this manner the two VPA measurements will be not be synchronized in any manner, so efficiency may not correctly track
fast changes to signals but will be accurate while both measurements are stable. In this option both measurements are
always continuous. Note that you can readily change to option #3 above by simply changing the MEAS MODE to SYNC VPA.
