Cirrus Logic AN356 - Manual

Copyright  Cirrus Logic, Inc. 2011
(All Rights Reserved)
http://www.cirrus.com
Application Note
CS1501 & CS1601:
DRIVING THE ZCD PIN FROM THE MOSFET DRAIN
1. Introduction
The CS1601 is designed with ZCD (zero-current detection), providing the controller with the capability to turn on the MOSFET
when the current through the boost inductor is close to zero. This can also be described as valley/zero crossings switching. This
is implemented by adding a sense winding on the PFC choke to detect the current.
If the addition of an auxiliary winding on the boost inductor is a problem due to design or manufacturing constraints, an alternative
method for implementing this function is presented below.
2. Standard ZCD Configuration
The standard configuration for the CS1501 & CS1601 is an auxiliary winding is added to the PFC boost inductor to provide zero-
current detection (ZCD) information.
Figure 1. ZCD Using Auxiliary Winding on PFC Boost Inductor
An auxiliary winding is added to the PFC boost inductor to provide zero-current detection (ZCD) information. The ZCD compar-
ator looks for the zero crossing on the auxiliary winding and switches when the auxiliary voltage is below zero. Switching in the
valley of the oscillation minimizes the switching losses and reduces EMI noise.
For a full description of ZCD operation, see the CS1501 & CS1601 data sheets.
R1
R2
R
cs
8 1
Boost Diode
Boost
FET
CS1501
CS1601
GD ZCD
IFB
GND
CS IAC
VDD
L
B
6
3
5 7
4
V
DD
STBY
2
V
rect
V
link
33pF
AN356
APR ‘11
AN356REV1