FLTR100V20 Filter Module
75 Vdc Input Maximum, 20 A Maximum
Data Sheet
March 2008
Adding additional components to the input filter to
improve performance usually has very limited payback,
and may actually increase the noise conducted onto
the input lines. Adding Y caps to the input side of the fil-
ter module couples any noise in the ground plane
directly into the input lines, usually degrading perfor-
mance. Adding additional X and Y caps to the power
module side of the filter module produces low-
impedance loops for high-frequency currents to flow,
possibly degrading performance.
Adding additional common-mode or differential-mode
filtering to the power module output leads decreases
the power module output noise, and also frequently
reduces the input noise by decreasing the noise cou-
pled from output leads to input leads. Common-mode
output filtering is particularly important if the load is tied
to chassis ground. If common-mode filtering is added
to the power module output, ensure that remote-sense
leads sense the output voltage before the common-
mode filter. Do not use remote-sense on the load side
of an output common-mode filter.
If input noise performance is unsatisfactory after apply-
ing the filter module as described previously, the best
remedy is to modify the layout and grounding scheme.
It is often useful to make a model of the power card,
using copper tape and a vector card, to experiment
with various layout and grounding approaches prior to
committing to a printed-wiring board.
Thermal Considerations
The case temperature must be kept below 100 °C.
Therefore for a particular current and ambient tempera-
ture, the airflow at the filter must be adequate.
Example:
Given: I
O, max
= 18 A; T
A, max
= 40 °C
Therefore �½T
, max
allowable = 60 °C
Determine airflow required (Figure 1): v = 1.0 m/s
(200 lfm)
Other Considerations
It is essential for good EMI performance that the input
lines not be contaminated with noise after passing
through the filter. Filtered input traces should therefore
be kept away from noise sources such as power mod-
ules and switching logic lines. If input voltage sense
traces must be routed past the power modules from the
quiet side of the filter module, they should be filtered at
the point where they leave the quiet input lines. Input
traces should be kept as far away from output power
traces as possible.
The fundamental switching frequency noise spike can
be somewhat reduced by adding a high-frequency
capacitor of a few microfarads across the input lines of
the filter module.
8
Lineage Power
LINEAGEPOWER [ LINEAGE POWER CORPORATION ]
