4Filter Modules Datasheet | www.gecriticalpower.com
Application
Conducted noise on the input
power lines can occur as either
dierential-mode or common-mode
noise currents. Dierential-mode noise is
measured between the two input lines,
and is found mostly at the lowfrequency
end of the spectrum. This noise
shows up as noise at the fundamental
switching frequency and its harmonics.
Common-mode noise is measured
between the input lines and ground
and is mostly broadband noise above
10 MHz. The high-frequency nature of
common-mode noise is mostly due to
the high-speed switching transitions
of power train components. Either or
both types of noise may be covered in a
specication, as well as a combination
of the two. An approved measurement
technique is often described, as well.
Dierential-mode noise is best
attenuated using a lter composed of
line-to-line capacitors (X caps) and series
inductance, provided by either a discrete
inductor or the leakage inductance of
a common-mode choke. In addition to
the dierential ltering provided by the
lter module, it is recommended that
an electrolytic capacitor be located at
the converter side of the lter to provide
additional attenuation of low-frequency
dierential noise and to provide a low
source impedance for the converter,
preventing input lter oscillations and
loadtransient induced input voltage dips.
Common-mode noise is best attenuated
by capacitors from power module input
to power module output, capacitors
from each input line to a shield plane
(Y caps), and common-mode chokes.
It is recommended that ceramic
capacitors be added around each
power module from each input and
output pin to a shield plane under
the module. The shield plane should
be connected to the CASE pin.
The GND pin of the lter module is
attached to Y caps within the module.
This pin should be tied to a quiet chassis
ground point away from the power
modules. GND of the lter module should
not be tied to the CASE pin of the power
module since this is a noisy node and
will inject noise into the lter, increasing
the input common-mode noise.
If no quiet grounding point is available,
it is best to leave the lter module GND
pin unattached. Each power system
design will be dierent, and some
experimentation may be necessary
to arrive at the best conguration.
Figure 5 shows a typical schematic
of a power module with lter
module and recommended external
components. Figure 6 is a proposed
layout. More than one power module
may be attached to a single lter
module as long as input current does
not exceed 5 A. Figure 7 shows the
recommended schematic for two power
modules attached to a single lter.
In applications where the addition of
input to output capacitors is undesirable,
do not use C3 and C4 shown in
Figures 5 and 6, and do not use C3,
C4, C8, and C9 shown in Figure 7.
In –48 V applications where the shield
plane and the power module case
must be tied to a signal, remove C1 in
Figures 5 and 6, remove C1 and C6 in
Figure 7, and connect the shield plane
and CASE pin to the VI(+) plane.
In +48 V applications where the shield
plane and the power module case
must be tied to a signal, remove C2 in
Figures 5 and 6, remove C2 and C7 in
Figure 7, and connect the shield plane
and CASE pin to the VI(–) plane.