Cirrus Logic AN359 - Manual

Copyright  Cirrus Logic, Inc. 2011
(All Rights Reserved)
http://www.cirrus.com
Application Note
EMI Filter Modifications when
Replacing L6562 with CS1501
1. Introduction
The Cirrus Logic CS1501 PFC controller is designed to match industry standard critical conduction mode (CRM)
power factor correction (PFC) controllers, with minimal change to conventional designs. This note summarizes the
changes required in the EMI filter circuit of a 120W power supply (PSU), when a ST Microelectronics L6562 PFC is
replaced with a Cirrus Logic CS1501 PFC controller.
2. Overview
When replacing the L6562 PFC controller, care must be taken to ensure the EMI signature is not compromised. Dif-
ferent PFC controllers operate at different frequencies and in different operating modes, requiring EMI filters with
different impedance profiles. An example of maintaining EMI signature when converting from the L6562 to the
CS1501 is described here. For the purpose of simplicity, we will consider only the PFC portion of the PSU circuit.
Cirrus Logic Application Note AN349 gives complete instructions on how to replace the L652.
3. Filter Structure
Figure 1 illustrates the components in an EMI filter for a PFC boost using ST Microelectronics L6562.
Figure 1. EMI Filter for a 120W PSU with an L6562 Analog PFC Controller
C
IN + Q
B
PFC
CONTROLLER
L
B
R
NTC
R
NTC
CM
Choke
DM
Choke
Y-CAP
Y-CAP
FUSE
C1
C2
C3
L1
C4
L2
C5
C
F
AC
X-CAP X-CAP X-CAP
V
DC_IN
AN359
JUL’11
AN359REV1