Infineon CoolSET ICE2QR 80 Series, CoolSET ICE2QR 65 Series Design Manual
Design Guide, Version 1.1, 8 August 2011
ICE2QRxx65/80x
Quasi Resonance CoolSET Design Guide
AN-PS0053
Power Management & Supply
N e v e r s t o p t h i n k i n g .
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: ICE2QRxx65/80x Design Guide
8 August 2011 V1.1
V1.0
Subjects (major changes since last revision)
Add ICE2QR0665Z, ICE2QR1065Z, ICE2QR1765Z, ICE2QR4765Z, ICE2QR0665G,
ICE2QR1765G and ICE2QR4765GZ
Revise typo
ICE2QRxx65/80x Quasi Resonance CoolSET Design Guide
License to Infineon Technologies Asia Pacific Pte Ltd
Winson Wong
Winson.wong@infineon.com
Eric Kok
Eric.kok@infineon.com
AN-PS0053
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Design Guide 3 8 August 2011
Quasi-resonant CoolSET design guide
ICE2QRxx65/80x
Table of Contents
1 Introduction.......................................................................................................5
2 CoolSET description.........................................................................................5
2.1 Main features.......................................................................................................................5
2.2 Pin layout.............................................................................................................................5
2.3 Pin functions .......................................................................................................................6
2.3.1 ZC (Zero Crossing)..........................................................................................................6
2.3.2 FB (Feedback).................................................................................................................6
2.3.3 CS (Current Sensing) ......................................................................................................6
2.3.4 Drain................................................................................................................................6
2.3.5 VCC (Power supply)........................................................................................................6
2.3.6 GND (Ground) .................................................................................................................6
3 Overview of quasi-resonant flyback converter ..............................................6
4 Functional description and component design .............................................8
4.1 VCC Pre-Charging and Typical VCC Voltage During Start-up .......................................8
4.1.1 VCC Capacitor.................................................................................................................9
4.2 Soft-Start..............................................................................................................................9
4.3 Normal Operation..............................................................................................................10
4.3.1 Switch-on Determination ...............................................................................................10
4.3.2 Switch-off Determination ...............................................................................................11
4.4 Active Burst Mode Operation..........................................................................................11
4.4.1 Entering Active Burst Mode Operation..........................................................................11
4.4.2 During Burst Mode Operation........................................................................................12
4.4.3 Leaving Active Burst Mode............................................................................................13
4.5 Current sense....................................................................................................................13
4.6 Feedback ...........................................................................................................................13
4.7 Zero crossing ....................................................................................................................13
4.8 Protections........................................................................................................................15
4.9 Others ................................................................................................................................15
5 Typical application circuit..............................................................................15
6 Input Power Curves for Quasi Coolset 650V/800V.......................................16
7 PCB Layout Recommendation.......................................................................22
8 Product Portfolio Quasi Resonant CoolSET®...............................................22
9 Design Equations............................................................................................23
10 References ......................................................................................................24
Design Guide 4 8 August 2011
Quasi-resonant CoolSET design guide
ICE2QRxx65/80x
1 Introduction
This design guide describes how to design quasi-resonant flyback converters using ICE2QRxx65/80x, which
is a new Quasi-resonant PWM CoolSET developed by Infineon Technologies
Firstly, the basic description of CoolSET will be given including the main features and Pin’s layout. Then an
overview of quasi-resonant flyback converter will be given, followed by the introduction of ICE2QRxx65/80x’s
functions and operations. A typical application example, input power curves, PCB layout recommendation,
product profolio and design equations will be given in the last part of this document.
2 CoolSET description
ICE2QRxxxx is a second generation quasi-resonant PWM CoolSET with power MOSFET and startup cell in a
single package optimized for off-line power supply applications such as LCD TV, and notebook adapter. The
digital frequency reduction with decreasing load enables a quasi-resonant operation till very low load. As a
result, the system average efficiency is significantly improved compared to conventional solutions. The active
burst mode operation enables ultra-low power consumption at standby mode operation and low output
voltage ripple. The numerous protection functions give a full protection of the power supply system in failure
situation. All of these make the ICE2QRxx65/80x an outstanding power CoolSET for quasi-resonant flyback
converter in the market.
In addition, numerous protection functions have been implemented in the CoolSET to protect the system and
customize the CoolSET for the chosen applications. All of these make the ICE2QRxx65/80x an outstanding
product for real quasi-resonant flyback converter in the market.
2.1 Main features
High voltage (650V/800V) avalanche rugged CoolMOS®with startup cell
Quasi-resonant operation
Load dependent digital frequency reduction
Active burst mode for light load operation
Built-in high voltage startup cell
Built-in digital soft-start
Cycle-by-cycle peak current limitation with built-in leading edge blanking time
Foldback Point Correction with digitalized sensing and control circuits
VCC undervoltage and overvoltage protection with Autorestart mode
Over Load /open loop Protection with Autorestart mode
Built-in Over temperature protection with Autorestart mode
Adjustable output overvoltage protection with Latch mode
Short-winding protection with Latch mode
Maximum on time limitation
Maximum switching period limitation
2.2 Pin layout
Figure 1 Pin configurations (top view), DIP-8 version; DIP-7 (Z) version; and DSO-12 (G) version;
Design Guide 5 8 August 2011
Quasi-resonant CoolSET design guide
ICE2QRxx65/80x
2.3 Pin functions
2.3.1 ZC (Zero Crossing)
Three functions are incorporated at the ZC pin. First, during MOSFET off time, the de-magnetization of the
transformer is detected when the ZC voltage falls below V
off, an output overvoltage fault will be assumed if VZCis higher than V
MOSFET on time, a current depending on the bus voltage flows out of this pin. Information on this current is
then used to adjust the maximum current limit. More details on this function are provided in Section 4.
2.3.2 FB (Feedback)
Usually, an external capacitor is connected to this pin to smooth the feedback voltage. Internally, this pin is
connected to the PWM signal generator for switch-off determination (together with the current sensing signal),
and to the digital signal processing for the frequency reduction with decreasing load during normal operation.
Additionally, the openloop/overload protection is implemented by monitoring the voltage at this pin.
2.3.3 CS (Current Sensing)
This pin is connected to the shunt resistor for the primary current sensing externally and it is also used to
determine the PWM signal generator for switch-off (together with the feedback voltage) internally. Moreover,
short-winding protection is realised by monitoring the Vcsvoltage during on-time of the main power switch.
(100mv). Second, after the MOSFET is turned
ZCCT
(3.7V). Finally, during the
ZCOVP
2.3.4 Drain
This pin is connected to the drain of the 650V/800V CoolMOS®.
2.3.5 VCC (Power supply)
The VCC pin is the positive supply of the CoolSET and should be connected to auxiliary winding of the main
transformer.
2.3.6 GND (Ground)
This is the common ground of the CoolSET. Note that the current sense resistor ground should be connected
to bulk capacitor ground in order to avoid strong noise interruption.
3 Overview of quasi-resonant flyback converter
Figure 2 shows a typical application of ICE2QRxx65/80x in quasi-resonant flyback converter. In this
converter, the mains input voltage is rectified by the diode bridge and then smoothed by the capacitor C
where the bus voltage V
windings (here one secondary winding Ws), and one auxiliary winding Wa. When quasi-resonant control is
used for the flyback converter, the typical waveforms are shown in Figure 3. The voltage from the auxiliary
winding provides information about demagnetization of the power transformer, the information of input
voltage and output voltage.
is available. The transformer has one primary winding Wp, one or more secondary
bus
bus
As shown in Figure 3, after switch-on of the power switch the voltage across the shunt resistor VCSshows a
spike caused by the discharging of the drain-source capacitor. After the spike, the voltage VCSshows
information about the real current through the main inductance of the transformer Lp. Once the measured
current signal VCSexceeds the maximum value determined by the feedback voltage VFB, the power switch is
turned off. During this on-time, a negative voltage proportional to the input bus voltage is generated across
the auxiliary winding.
Design Guide 6 8 August 2011
Quasi-resonant CoolSET design guide
ICE2QRxx65/80x
85 ~ 265 VAC
Dr1~D
r4
ZC
Power Management
W
C
bus
CZCR
ZC2
R
ZC1
VCC
Snubber
R
VCC
C
VCC
Startup Cell
D
VCC
Drain
p
W
a
D
O
W
s
C
O
C
PS
R
b1
L
f
V
C
O
f
PWM controller
CS
®
R
CS
Optocoupler
R
R
b2
ovs1
R
c1
FB
Cc1C
TL431
c2
R
ovs2
GND
Current Mode Control
Cycle-by-Cycle
current limitation
Zero Crossing Block
Active Burst Mode
Protections
Control Unit
CoolMOS
CoolSET®-Q1
Figure 2 Typical Application of ICE2QRxx65/80x
The drain-source voltage of the power switch Vdswill rise very fast after MOSFET is turned off. This is caused
by the energy stored in the leakage inductance of the transformer. A snubber circuit, RCD in most cases, can
be used to limit the maximum drain source voltage caused. After the oscillation 1, the drain-source voltage
goes to its steady value. Here, the voltage v
is the reflected value of the secondary voltage at the primary
Refl
side of the transformer and is calculated as:
VV
V
(1)
Refl
doout
n
where n the turns ratio of the transformer, which is defined in this document as:
/NNn
PS
(2)
with Npand Nsare the turns count of the primary and secondary winding, respectively.
After the oscillation 1 is damped, the drain-source voltage of the power switch shows a constant value of
V
bus+VRefl
t
off1
until the transformer is fully demagnetized. This duration builds up the first portion of the off-time
.
After the secondary side current falls to zero, the drains-source voltage of the power switch shows another
oscillation (oscillation 2 in Figure 3, this is also mentioned as the main oscillation in this document). This
oscillation happens in the circuit consisting of the equivalent main inductance of the transformer Lpand the
capacitor across the drain-source (or drain-ground) terminal CDSwhich includes C
of the MOSFET. The
o(er)
frequency of this oscillation is calculated as:
f
(3)
OSC2
The amplitude of this oscillation begins with a value of v
1
CL2π
DSP
and decreases exponentially with the elapsing
Refl
time, which is determined by the losses factor of the resonant circuit. The first minimum of the drain voltage
appears at the half of the oscillation period after the time t4and can be apporximated as:
V-VV
ReflbusdsMin
(4)
In the quasi-resonant control, the power switch is switched on at the minimum of the drain-source voltage.
From this kind of operation, the switching-on losses are minimized, and switching noise due to dVds/dt is
reduced compared to a normal hard-switching flyback converter.
Design Guide 7 8 August 2011
Quasi-resonant CoolSET design guide
ICE2QRxx65/80x
Figure 3 Key waveforms of a quasi-resonant flyback converter
4 Functional description and component design
4.1 VCC Pre-Charging and Typical VCC Voltage During Start-up
In the CoolSET ICE2QRxx65/80xx, a startup cell is integrated to the CoolMOS. The startup cell provides a
pre-charging of the VCC capacitor till VCC voltage reaches the VCC turned-on threshold V
CoolSET begins to operate.
Once the mains input voltage is applied, a rectified voltage shows across the capacitor C
device provides a current to charge the VCC capacitor C
. Before the VCC voltage reaches a certain value,
vcc
. The high voltage
bus
the amplitude of the current through the high voltage device is only determined by its channel resistance and
can be as high as several mA. After the VCC voltage rises to certain level, the CoolSET controls the startup
cell so that a constant current around 1mA is provided to charge the VCC capacitor. It stops until the VCC
voltage exceeds the turned-on threshold V
. As shown in the time phase I of Figure 4, the VCC voltage
VCCon
increase almost linearly.
The time taken for the charging VCC to turn-on threshold can then be approximately calculated as:
CV
VCCVCCon
where I
t [5]
1
I
VCCcharge2
VCCcharge2
is the charging current from the startup cell which is 1.1mA, typically.
Design Guide 8 8 August 2011
VCCon
and the
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