AN372 - Efficient Surge/ESD protection for charging lines in mobile devices

ES D3 07 - U 1 -02 N E S D31 1 - U1- 02N
Effici ent S ur ge/ ES D p rot ec ti on fo r
chargi ng l ines in mo bile d e vic es
Applic atio n N ote A N 372
Revision: 1.1, 2014-10-21
http://www.infineon.com/RFandProtectionDevices
RF and P r otecti on D evic es
Edition 2014-10-21
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Application Note AN372
Efficient Surge/ESD protection for charging lines in mobile devices
Application Note AN372
Revision History: V1.0 2014-04-29
Revision: 1.1 2014-10-21
Page
Subjects (major changes since last revision)
16
Chapter 5 added, general update
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Last Trademarks Update 2011-11-11
Application Note AN372, Rev. 1.1
3 / 15
2014-10-21
Application Note AN372
Efficient Surge/ESD protection for charging lines in mobile devices
Table of Content
1
Customized Surge and ESD Protection for USB VBUS Line............................................................ 5
2
2.1
2.2
Over-voltage protection in a mobile device extended with a Surge protection TVS diode ....... 6
Surge Transients .................................................................................................................................. 6
What is OVP and how does it work? .................................................................................................... 6
3
3.1
3.2
3.3
Uni-directional TVS diode ESD307-U1-02N and ESD311-U1-02N .................................................. 8
Features of the ESD307-U1-02N ......................................................................................................... 8
Features of the ESD311-U1-02N ......................................................................................................... 8
IEC61000-4-5 Surge and TLP characteristics of the ESD307 and ESD311 ....................................... 9
4
4.1
4.2
Design of Experiment and Simulations ......................................................................................... 10
Simulation of IEC61000-4-5 “short circuit 8µs/20µs” Surge Current Discharge ................................ 10
Simulation of the Surge clamping voltage across the TVS ................................................................ 12
5
Surge Peak Power – the Mystery .................................................................................................... 13
6
Authors: ............................................................................................................................................ 14
List of Figures
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
ESD/surge current distribution via ESD/surge diode and IC based ESD protection ........................... 5
USB charging chain in the Mobile Phone for the Quick Charge 9V mode........................................... 7
Correlation between charging mode and TVS characteristic ............................................................... 7
IEC61000-4-5 Surge and TLP characteristics of the ESD307-U1 and the ESD311-U1...................... 9
Schematics of the Surge Generator connected to the DUT (1Ohm resistor). ................................... 10
Functional structure of the 8/20us Surge Generator short circuit version.......................................... 10
Surge current,- clamping voltage, dissipated power and energy simulated for a DUT of 1 Ohm ...... 11
Surge current, Surge clamping voltage, dissipated power and energy simulated for a TVS diode
affected with an 8µs/20µs surge strike according IEC61000-4-5 ...................................................... 12
Correlation between Ip_max , Vp_clamp_max and maximal peak power. ................................................... 13
Application Note AN372, Rev. 1.1
4 / 15
2014-10-21
Application Note AN372
Efficient Surge/ESD protection for charging lines in mobile devices
1
Customized Surge and ESD Protection for USB VBUS Line
Over the last years, enormous amount of mobile devices, Set-Top-Boxes and Smart-TVs have been brought
into the market. Most such devices support USB2.0/3.0 as Data Exchange Interface. Most mobile devices such
as mobile phones, phablets, tablets, navigators and smart-watches use USB Interface to provide connectivity to
other electronic devices and for charging purposes. Generally for all plug-in/plug-out electronic interfaces,
electrostatic discharge (ESD) and surge discharge are widespread threats. An overvoltage failure caused by
such a strike can hit the interface connectors directly or hit the internal electronic circuits via the user interface.
This interface can be a keypad, touch screen, LC-display or LAN-Cables connected to the desktop stations.
The effect of these ESD/Surge strikes can be permanent performance degradation or even a destruction of the
interface circuit, resulting in a failure of the entire electronic device. Therefore a reliable combination of ESD and
surge protection is obligatory and should be taken into account from the very beginning of the electronic
device’s design phase.
ESD protection is integrated inside the IC too – but only for device handling protection. To protect the equipment
in the field, a smart ESD/Surge protection approach distributes the failure current between a tailored external
ESD/Surge protection circuit and the small ESD protection in the IC. The internal ESD protection structure can
be very small because it has to handle only weak ESD strikes e.g. (2kV HBM), which may occur during
manufacturing and board assembly (refer to Figure 1).
ESD current IESD
[email protected]
PCB line
[email protected]
Figure 1
[email protected]
=
[email protected]
DUP
[email protected]
IC I/O
ESD prot.
ESD/surge current distribution via ESD/surge diode and IC based ESD protection
Moving forward in miniaturization of semiconductor structures, ESD/Surge handling capability of miniaturized
semiconductor structures is reduced accordingly. Today, I/Os are tailored to be 2kV ESD safe according to
HBM (Human Body Model - JEDEC standard JS-001.). Safety margin is reduced more and more moving
forward from one technology node to the other.
To achieve SURGE protection capability, a combination of external ESD/surge protection is mandatory anyway
to handle the huge dissipated energy generated by the surge strike impact. An IC with built-in surge handling
capability would require an extension of expensive IC chip area. Finally, chip area to realize basic functionality
would be the minor one.
The combination of external ESD/surge diode with internal ESD handling protection keeps the high required
ESD/Surge protection capability alive. The required ESD/Surge structure on the die is minimized. Furthermore
this two-step ESD/Surge approach enables the designer to pass high system level ESD/Surge requirements
according to IEC61000-4-2 and IEC61000-4-5. Various applications demand different ESD/Surge protection
devices. So the selection of the right ESD/surge diode is tailored to the application and to the internal IC based
ESD protection circuit.
Application Note AN372, Rev. 1.1
5 / 15
2014-10-21
Application Note AN372
Efficient Surge/ESD protection for charging lines in mobile devices
2
Over-voltage protection in a mobile device extended with a Surge
protection TVS diode
2.1
Surge Transients
Commonly a surge discharge is an unwanted electrical transient, transmitting high amount of energy and can
show an amplitude of several hundred volts. For device characterization, a dedicated reference surge pulse
waveform is postulated providing a similar energy as the real transients hiding the device (e.g. USB VBUS line).
For the so called “short circuit 8µs/20µs” reference surge pulse, we are facing an entire pulse duration of less
than 100µs. Other norm surge pulses show a “5µs/360µs” and a “10µs/700µs” characteristic and provide much
higher energy to the subsequent device.
In the following discussion we are discussing about the “short circuit 8µs/20µs” surge strike stated in IEC610004-5.
The surge, also known as glitch, can have either positive or negative polarity. Significant overshoot and / or
undershoot in reverse polarity is also possible. Such voltage surges often occur in unstable power networks
between building networks. Furthermore, surges on the Vcc line can be generated in case of load alternation.
Surge transients can damage, destroy and cause malfunction of any personal, commercial electronic as well as
any industrial facilitiy.
A basic origin of a surge is power switching between the electrical units inside facilities or buildings such as
household appliances or their switch mode power supply (SMPS). Power switching of electrical loads (On/OffState) may not result in a surge of enormous energy but due to their frequent presence, they may damage the
equipment over some period of time. Common sources of surge from the outside networks are, lightning events
and power surges on the LAN cables and their transformer units. Most of the recent high-end mobile phones
use a wall-plug USB-adapter to charge/fast-charge/ultra-fast-charge their battery cells. Plug-in and plug-out
of the USB cable in the USB-adapter results in power switching (load alternation) in the DC/DC converter
module followed by a surge on the VBUS-Line.
2.2
What is OVP and how does it work?
For a mobile device, the Over-Voltage-Protection (OVP) is a mandatory feature. The OVP functionality can be
implemented in a dedicated OVP IC, direct at the Vbus input, or integrated in the charger IC or in the PowerManagement-Unit (PMU). The job of the OVP is to separate the subsequent low voltage section e.g. charger
unit, or PMU in case of an overvoltage on Vbus.
Such an OVP basically consists of a Field-Effect-Transistor (FET) connected in series and a built-in control unit
(comparator) which senses the input voltage and controls the gate region of the transistor. In case the input
voltage rises above the adjusted threshold, the control unit switches the FET in open state to turn the
subsequent circuit structure (e.g. PMU) into unpowered mode and protect it from the overvoltage transient on
the USB VBUS Line.
Optionally OVPs protect battery cell from unintentional discharge by blocking any reverse-current from a battery
cell.
Limitation of input voltage for the OVP functionality is based on the semiconductor process used. In typical
designs, often a maximum input voltage VIN-max of about 25V…30V is stated. Exceeding this range, the OVP
block will be damaged (Figure 2).
In case of a surge event, charging voltage on the Vbus line rapidly rises and the FET is switched off. Finally the
transient voltage on the Vbus line exceeds VIN-max and will damage the OVP section. Furthermore the internal
FET can move into conducting mode and the surge is transferred to the subsequent PMU. The PMU is not
designed to withstand any voltage higher than the charging voltage and will be damaged immediately as well.
Therefore it is highly recommended to use an appropriate surge Protection mechanism in USB Charging Chain
consisting of a TVS Diode in addition to the OVP Unit. As a result of having a TVS Diode connected in front of
the OVP function block to GND, the surge pulse is facing NO open-circuit (provided by the serial MOSFET) any
more. The surge energy is shunted to GND. The surge clamping voltage @ the OVP input is controlled by the
TVS diode characteristic and MUST not exceed the maximum working voltage of the OVP.
Application Note AN372, Rev. 1.1
6 / 15
2014-10-21
Application Note AN372
Efficient Surge/ESD protection for charging lines in mobile devices
Specification of the surge TVS diode is given for the “8µs/20µs” use-case. For a stated maximum peak surge
current, peak clamping voltage should be minimized.
Battery Charger
OVP-function
USBVbus
VIN-max = 30V
over voltage
surge injection
VOUT-max = 10V
PMU
V_IN-max-PMU = 12V
Threshold to
open FET = 10V
control
Surge TVS
VRWM e.g. 15V
Vclamping-surge < 30V
Figure 2
PMU outputs
Mobile Phone - Quick charge chain - 9V mode
USB charging chain in the Mobile Phone for the Quick Charge 9V mode
Maximum required working voltage of the surge TVS depends on the application. From system point of view the
TVS diode characteristic is defined in this way:
1. Maximum TVS surge clamping voltage Vpeak_max @ requ. surge current Ipeak < Vin-max of the OVP
2. Maximum working voltage VRWM of TVS > max charging voltage / maximum threshold voltage of OVP
Charging voltage is defined according the charging mode

Standard:
5V, 0.5A typ. up to 1.5A

Quick-Charge 1.0/2.0:
5V/9V/12V/20V (Notebook), up to 5A

USB-Power Delivery (PD):
5V/9V/12V/20V (Notebook), up to 5A
The TVS diode is a device to protect the OVP function regarding short transient e.g. ESD, surge strikes, but is
not able to handle a faulty charger DC voltage. This job is served by the OVP function up to maximum input
voltage of the OVP (Vin-max ).
Taking a certain DC charging voltage failure on the Vbus line into account (OVP and TVS are in isolating mode),
maximum working voltage of the TVS (VRWM ) should be considerably higher than the nominal maximum
charging voltage, BUT surge clamping voltage must be lower than the stated V IN-max of the OVP unit to avoid
any destruction of the OVP (requirement #1)
Surge TVS clamping
voltage window,
limited by:
V_IN-max of OVP
charging voltage
failure tolerance
e.g. 30V
e.g. VRWM=15V
Example:
For a standard 5V charging, VRWM should be about
10V…12V (ESD307).
In case of fast charging, VRWM of the Surge TVS diode
has to be adjusted above the highest threshold voltage
of the OVP, defined by the highest fast-charging mode.
For a 9V quick charge mode the ESD311 fits perfect.
e.g. 9V
max. charging mode
Figure 3
Correlation between charging mode and TVS characteristic
Application Note AN372, Rev. 1.1
7 / 15
2014-10-21
Application Note AN372
Efficient Surge/ESD protection for charging lines in mobile devices
3
Uni-directional TVS diode ESD307-U1-02N and ESD311-U1-02N
These uni-directional TVS diodes are designed for a wanted signal between ~0 V and their “maximum working
voltage”. The ESD protection capability is granted for a uni-directional diode for positive AND negative ESD
strikes in the same way. Most standard data signaling, Vcc supply, are unidirectional signals. As long as the
signal is maintained between zero and its maximum voltage, the diode is switched off. By exceeding its value all
signal line content, accordingly wanted signal plus failure current, are driven through the diode into ground. In
case of a negative failure current, every signal with amplitude higher than 0.7 Volts is driven through the diode
into ground.
3.1
Features of the ESD307-U1-02N
• ESD / Transient / Surge protection according to:
– IEC61000-4-2 (ESD): ±30 kV (air / contact discharge)
– IEC61000-4-4 (EFT): ±80 A (5/50 ns)
– IEC61000-4-5 (surge): ±34 A (8/20 μs)
• Uni-directional working voltage up to VRWM = 10 V
• Low capacitance: CL = 270 pF (typical)
• Low clamping voltage VCL < 24 V
• Low leakage current IR = < 100 nA (typical)
• Small and flat-profile SMD plastic package: 1.6 mm x 0.8 mm x 0.375 mm.
• Pb-free (RoHS compliant) and halogen free package
3.2
Features of the ESD311-U1-02N
• ESD / Transient / Surge protection according to:
– IEC61000-4-2 (ESD): ±30 kV (air / contact discharge)
– IEC61000-4-4 (EFT): ±4 kV / ±80 A (5/50 ns)
– IEC61000-4-5 (surge): ±28 A (8/20 μs)
• Uni-directional working voltage up to VRWM = 15 V
• Low capacitance: CL = 210 pF (typical)
• Low clamping voltage VCL < 29 V at IPP = 28 A
• Low leakage current IR = < 100 nA (typical)
• Small and flat-profile SMD plastic package: 1.6 mm x 0.8 mm x 0.375 mm.
• Pb-free (RoHS compliant) and halogen free package
Application Note AN372, Rev. 1.1
8 / 15
2014-10-21
Application Note AN372
Efficient Surge/ESD protection for charging lines in mobile devices
3.3
IEC61000-4-5 Surge and TLP characteristics of the ESD307 and ESD311
Below a 8µs/20µs “short circuit” and TLP discharge characteristic presented.
Rdyn-TLP = 0.10 Ω
Rdyn-surge = 0.30 Ω
Figure 4
Rdyn-TLP = 0.10 Ω
Rdyn-surge = 0.32 Ω
IEC61000-4-5 Surge and TLP characteristics of the ESD307-U1 and the ESD311-U1
The dynamic resistance Rdyn-surge in case of IEC610004-5 8µs/20µs surge test is significant higher compared to
the dynamic resistance evaluated in IEC61000-4-2 test or in the TLP test. The increase of Rdyn-surge is caused by
self heating effects of the TVS/surge diode because of the long surge pulse duration (according IEC61000-4-5).
For an ESD strike according IEC61000-4-2 or an TLP pulse the generated heat is much lower (because
dissipated energy of an ESD strike is much lower) and limited to a certain small chip area only. For surge
testing, dissipated energy is spread inside the entire chip and is fed to the leads. The heating effect of the chip
and especially the active chip area is much higher in case of a surge strike. For surge robustness a package
showing low thermal resistance is very important.
Application Note AN372, Rev. 1.1
9 / 15
2014-10-21
Application Note AN372
Efficient Surge/ESD protection for charging lines in mobile devices
4
Design of Experiment and Simulations
4.1
Simulation of IEC61000-4-5 “short circuit 8µs/20µs” Surge Current Discharge
The surge specification IEC61000-4-5 covers several different test scenarios. In one scenario, we have the
surge tests working with a pulse length (pulse comes down to 50% of peak value) of 20µs (short circuit) and
50µs (open circuit). Another scenario shows a much longer ESD strike duration. Here the surge strike should
emulate the effect of a lightning. The pulse length is 700µs (open circuit) and about 350µs (short circuit). The
rise time of the “lightning” strike is up to 10µs. Based on their very long pulse duration the energy of such pulses
is extremely high .
In this subsection, the working principle of the ESD source / -generator according IEC61000-4-5 “short circuit”
8µs/20µs is explained. The ESD test generator shown as a black box model, connected to the DUT (Device
Under Test) is presented in the Figure 5. To judge the exact waveform of the surge strike, a 1 Ohm resistor is
used for the DUT.
Figure 5
Schematics of the Surge Generator connected to the DUT (1Ohm resistor).
The electrical equivalent circuit of the IEC61000-4-5 combined surge generator for a short current waveform
(8µs/20µs) and an open circuit waveform (1.2µs/50µs) is shown in Figure 6.
Internal and external wire connection adds about 0.5…1 Ohm serial resistance (R_cable) at the generator
output. Taking this into account, the generator output resistor (in front of R_shunt) is about 2 Ohm. This fits
exactly with the output resistance specification of an IEC61000-4-5 combined wave surge generator.
8/20µs-short cir. and 1.2/50µs open-cir. combination wave generator
trigger
Lr=10.4uH
Rc=1K
R_cable R_shunt and Rs to provide
0.5...1
„short circuit“ waveform
Ohm
Rs
Figure 6
V_clamp
R_shunt
~0.5 Ohm
R2=19.8
R1=25.1
Cc=6uF
ESD
voltage
surge
current
DUT
A
Rm1=0.94
Functional structure of the 8/20us Surge Generator short circuit version.
To generate the exact waveform in “short circuit mode” an assisting “R_shunt” (~0.5 Ohm) is necessary to
provide a “defined short” independent of the DUT impedance.
The lower the R_cable and the shunt resistance are, the higher the under-swing will be. In most real testequipment, there is NO or only a minimum under-swing. An “under-swing” is not mandatory but possible up to
30% respective peak level in IEC61000-4-5 specification for 8µs/20µs “short circuit” surge strike.
To adjust the surge current to the required test range, a serial resistor is placed in front of the DUT. Furthermore
the surge current into the DUT can be measured in an easy way via the serial resistor.
Finally the “short circuit” surge current waveform according IEC61000-4-5 is simulated and the dissipated power
in the DUT caused by the (8µs/20µs) Surge pulse is presented. The dissipated power is presented in Watt and
normalized to 1 Ohm DUT/Load resistance. The total energy of the ESD discharge is calculated and given in
MILI-Joules. The simulated waveforms are illustrated in Figure 7. The voltage drop / clamping voltage across
the DUT is monitored as well.
Application Note AN372, Rev. 1.1
10 / 15
2014-10-21
Application Note AN372
Efficient Surge/ESD protection for charging lines in mobile devices
8µs/20us surge current into DUT [A]
30
25
“Short Circuit” waveform – 30A peak current
into 1 Ohm DUT/Load
I_DUT.i, A
20
15
10
5
0
-5
0
10
20
30
40
50
60
70
80
90
100
time, usec
Clamping Voltage @ DUT für surge current [V]
30
25
ESD clamping voltage @ DUT=1 Ohm load for a
30A peak current “short circuit” surge pulse
V_DUT, V
20
15
10
5
0
-5
0
10
20
30
40
50
60
70
80
90
100
time, usec
8µs/20us surge power I*U [W]
1000
Dissipated power of a 30A peak current surge
pulse, normalized to 1 Ohm DUT / Load resistance
surge_DUT_power
800
Pdiss _ DUT  VDUT  I ESD
600
100us
P
Ediss_DUT 
400
diss_DUT
 11mJ / OhmDUT
0ns
200
0
0
10
20
30
40
50
60
70
80
90
100
time, usec
Figure 7
Surge current,- clamping voltage, dissipated power and energy simulated for a DUT of 1 Ohm
Application Note AN372, Rev. 1.1
11 / 15
2014-10-21
Application Note AN372
Efficient Surge/ESD protection for charging lines in mobile devices
4.2
Simulation of the Surge clamping voltage across the TVS
The same procedure is done for the surge discharge.
In the next step the 1 Ohm DUT is replaced by the TVS/Surge Diode. The TVS/surge diode (Ubreakdown=12V,
Rdyn-surge=0.35 Ohm) was tested with an 8µs/20µs surge strike according IEC61000-4-5. Peak surge current was
adjusted to 30A. Dissipated power of the surge strike in the TVS/surge diode was calculated. The total energy of
the surge discharge was calculated and given in MICRO-Joule. The simulated waveforms are illustrated in
Figure 8. The voltage drop / clamping voltage across the ESD/Surge diode is monitored as well.
I_TVS [A],
m1
V-clamp_at TVS [V]
30
30
m2
25
peak current (Ip)
m1
time=7.959usec
I_TVS.i=29.943
25
20
m2
time=8.119usec
V_TVS=23.399
peak clamping
voltage @ Ip
15
15
10
10
5
5
0
0
-5
V_TVS, V
I_TVS.i, A
20
-5
0
10
20
30
40
50
60
70
80
90
100
time, usec
8µs/20us surge power I*U [W]
800
peak power
700
Dissipated power of a 30A peak current
surge pulse in the TVS Diode
surge_TVS_power
600
500
Pdiss _ DUT  VDUT  I ESD
400
100us
300
Ediss_DUT 
200
P
diss_DUT
 11mJ
0ns
100
0
-100
0
10
20
30
40
50
60
70
80
90
100
time, usec
Figure 8
Surge current, Surge clamping voltage, dissipated power and energy simulated for a
TVS diode affected with an 8µs/20µs surge strike according IEC61000-4-5
Application Note AN372, Rev. 1.1
12 / 15
2014-10-21
Application Note AN372
Efficient Surge/ESD protection for charging lines in mobile devices
Surge Peak Power – the Mystery
5
As we learned, dissipated power for an ESD/surge diode (DUT) is related to ESD/surge current IESD through the
protection device times clamping voltage (VDUT) across the protection device.
Pdiss_ DUT  VDUT  I ESD
Finally the dissipated energy Ediss_DUT is the integral of Pdiss_DUT over time (duration of the surge strike)
100us
Ediss_DUT 
P
diss_DUT
0ns
Peak power is simply the maximum current - Ipeak - times maximum clamping voltage - Vpeak –
Because the system is acting resistive, - Ipeak – and - Vpeak –are present at the same time (NO phase shift).
Ppeak  V peak _ clamp  I peak
Maximum peak power is simply
Comparing two diodes designed for the same working voltage (e.g. 12V). Both diodes can withstand a
maximum peak current Ip_max of 30A.

Diode-A is rated with a max. peak power (Ppeak_max ) of 900W,
Maximum Peak clamping voltage Vp_clamp_max for diode-A is 30V
Ppeak _ max_ Diode A  V peak _ max_ Diode A  I peak_max  30V * 30 A  900 Watt

Diode-B is rated with a max. peak power (Ppeak_max ) of 630W
Maximum Peak clamping voltage Vp_clamp_max for diode-B is 23V
Ppeak _ max_ Diode B  V peak _ max_ Diode B  I peak_max  23V * 30 A  690 Watt
m1
I_TVS [A],
V-clamp_at TVS [V]
8µs/20us surge power I*U [W]
30
800
30
m2
25
peak current (Ip)
m1
time=7.959usec
I_TVS.i=29.943
peak power
700
25
peak clamping
voltage @ Ip
15
15
10
10
5
5
0
0
-5
-5
V_TVS, V
I_TVS.i, A
20
m2
time=8.119usec
V_TVS=23.399
surge_TVS_power
600
20
500
400
300
200
100
0
10
20
30
40
50
60
70
80
90
0
-100
0
100
10
20
30
time, usec
Figure 9
40
50
60
70
80
90
100
time, usec
Correlation between Ip_max , Vp_clamp_max and maximal peak power.
It is obvious, diode-B shows higher surge protection performance, because Vp_clamp_max at given Ip_max is lower.
The lower Vp_clamp is, the lower the residual surge stress is for the subsequent device e.g. I/O port is.
Diode-B shorts the surge energy better to GND.
 It is highly recommended to select diode-B for effective surge protection eventhough the
maximum dissipated power is lower for diode-B
To select a TVS diode for surge protection, the maximum peak power is not the right criteria. It is more
important to check the peak clamping voltage at a given peak surge current.
According to Figure 1, it is obvious that the lower the TVS clamping voltage is, lower the clamping voltage
(residual ESD stress) at the IC based TVS diode will be.
Application Note AN372, Rev. 1.1
13 / 15
2014-10-21
Application Note AN372
Efficient Surge/ESD protection for charging lines in mobile devices
6
Authors:
Sergey Karpov
Alexander Glas
Application Engineer of Business Unit “RF and Protection Devices”
Principal Engineer for Protection at RPD
Application Note AN372, Rev. 1.1
14 / 15
2014-10-21
w w w . i n f i n e o n . c o m
Published by Infineon Technologies AG
AN372
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