QM range App Note, document number 260283, rev 15
Page 38 of 48
Installation for Optimum EMC Performance
Mounting
All equipment ideally should be mounted inside an earthed shielded metal box. Alternatively an earthed metal
plate can be used to mount the power supply and load.
EMC Susceptibility
To reduce susceptibility to electrical fast transients fit a 120uF low ESR cap across the output terminals of Ch2
of the 12/12 DM module.
Cables
All cables (AC input, DC output, remote sense and signal) should be run as close as possible to the earthed
metal box/plane.
AC input cable should be a twisted group laid as flat to the earthed metal box/plane as possible.
Run the remote sense and power output cables as separate pairs twisted tightly together with at least 1 twist per
centimetre. Keep separate from the input cables. If the input and output cables must be run close to each other
screen one (or ideally both).
All cable run loops should be kept as small as possible (this should be implemented in the system PCB design
also).
The radiated emissions performance may be further improved by fitting ferrite clamps to each of the input and
output cables.
Example parts which can be used are
TDK ZCAT3035-1330
TDK ZCAT2436-1330
PMBus™ Option
The PMBus™ Clock and Data rise and fall times can be as fast as 20 ns, with a clock frequency of 100 kHz.
TDK-Lambda recommends that the appropriate precautions are taken to improve EMC performance. The
following will help with both emissions and immunity performance when the PMBus™ feature is used:
All communications cables should be kept as short as possible.
Good practice should be used in laying out an
y system PCB’s containing the communications bus.
For the communications cable, use screened cable with the screen connected to ground at the QM
PMBus™ interface end, or at both ends.
If an unscreened communications cable is used it should not be run in parallel with other cables in the
system.
If USB -
PMBus™ Adaptors are used, care should be taken in their placement, as these can cause
interference problems. For the purpose of EMC testing, TDK-Lambda recommends a screened box to
reduce its emissions.
Any system components that are known to be sources of interference should be physically separated from the
PMBus™ cabling.
Connecting between boxes
If cables must be connected between equipment boxes, then at the closest possible point to the port where the
cables exit the 1st enclosure connect 100nF decoupling Y caps (between the output and earth). Note that these
capacitors must be rated at the working voltage. Ideally these capacitors should be between all signal cables
which have to connect between boxes although this may not be practical if fast switching [digital] signals are
involved (if this is the case then smaller value Y capacitors should be used).
