QPI-6L Datasheet, PDF (3/8 Pages) Vicor Corporation – 14 Amp Active EMI Filter for 48V DC Bus

Applications Information
The QPI-6 is an active EMI filter providing conducted
common-mode and differential-mode attenuation
from 150 kHz to 30 MHz. The QPI-6 attenuates noise at
all frequencies covered by EN55022. Designers should
be aware that to select and qualify an EMI filter they
must test the filter in their equipment under the set up
and conditions specified in the EMI standards that they
are trying to meet.
Filter performance is highly dependent on several
factors and cannot be derived from the attenuation
curves shown in Figure 2 alone. Performance is a
complex function of filter element impedances and
noise source impedances, which vary in magnitude and
phase over the frequency spectrum. Measurements
should be made in consultation with in-house
compliance testing or an independent EMI test facility.
Test Example
Figures 3 and 4 show the before and after plots of a
DC-DC converter noise profile to demonstrate the
performance of the QPI-6. The plots were taken using
the standard measurement technique and set up defined
in CISPR22. The results show the total noise spectrum
for a standard DC-DC converter under load compared
to the EN55022 Class B Quasi-peak detection limit.
Figure 3 – Conducted EMI profile of a DC-DC Converter
without filter.
The resulting plot in Figure 4 shows the QPI-6 is
effective in reducing the total conducted noise
spectrum measured pre-filter to well below the
EN55022 Class B Quasi-peak detection limit.
Picor Corporation • www.picorpower.com
Figure 4 – Conducted EMI profile of a DC-DC Converter
with QPI-6.
Layout and Circuit
Application of the QPI-6 requires PCB layout practices
similar to those used with passive EMI filters. The circuit
in Figure 6 and the PCB layout in Figures 9 & 10 should
be used as a design guide to ensure successful
application of the QPI-6. Refer to the application note
QPI- AN1 for additional PCB layout recommendations.
Note: For optimum performance of the QPI-1 it is critical
to connect the QPI-1 Shield Plane (pins 5 & 6) to the
converter EMI Shield Plane (common point of C1-C4 "Y"
capacitors) thru RY as shown in Figure 6. If the safety
earth-ground connection (chassis or case) is connected in
the power conversion section of the PCB it should be at
the input bus of the QPI-1 Shield Plane, shown as the
optional connection in Figure 6. Connecting the converter
EMI shield plane directly to chassis ground may degrade
the QPI-1 attenuation performance. The typical value for
RY is 10 Ohms. The recommended part is a 5% tolerance
SMT1206 or similarly rated 0.25 W through-hole resistor.
Some systems may require the converter positive or
negative input or an output "terminal" to be connected to
PE (Protective Earth) ground for safety or other
considerations. When using the QPI in this situation this
"terminal" must be connected to the converter shield
plane created in the PCB layout under the converter.
Because the PE earth path may pass excessive current
under a fault condition the resistance of this path may be
limited to a low resistance value. To meet the resistance
requirement without degrading filter performance Ry can
be replaced by a 4.7uH inductor rated for the fault current
condition maintaining low power dissipation during a
fault until the protection device clears.
QPI-6L Data Sheet Rev. 2.0 Page 3 of 8