1. Product profile
1.1 General description
Low capacitance unidirectional ElectroStatic Discharge (ESD) protection diodes in a
SOD523 (SC-79) ultra small and flat lead Surface-Mounted Device (SMD) plastic package
designed to protect one signal line from the damage caused by ESD and other transients.
1.2 Features
1.3 Applications
PESD5Zx series
Low capacitance unidirectional ESD protection diodes
Rev. 02 — 4 April 2008 Product data sheet
Table 1. Product overview
Type number Package Configuration
NXP JEITA
PESD5Z2.5 SOD523 SC-79 single
PESD5Z3.3
PESD5Z5.0
PESD5Z6.0
PESD5Z7.0
PESD5Z12
nESD protection of one line nLow leakage current: IRM <1nA
nLow diode capacitance nESD protection up to 30 kV
nMax. peak pulse power: PPP = 260 W nIEC 61000-4-2; level 4 (ESD)
nLow clamping voltage: VCL =15V nIEC 61000-4-5 (surge); IPP =20A
nComputers and peripherals nPortable electronics
nAudio and video equipment nSubscriber Identity Module (SIM) card
protection
nCellular handsets and accessories nFireWire
n10/100/1000 Mbit/s Ethernet nHigh-speed data lines
nCommunication systems
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 2 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
1.4 Quick reference data
2. Pinning information
[1] The marking bar indicates the cathode.
3. Ordering information
Table 2. Quick reference data
T
amb
=25
°
C unless otherwise specified.
Symbol Parameter Conditions Min Typ Max Unit
Per diode
VRWM reverse standoff voltage
PESD5Z2.5 - - 2.5 V
PESD5Z3.3 - - 3.3 V
PESD5Z5.0 - - 5.0 V
PESD5Z6.0 - - 6.0 V
PESD5Z7.0 - - 7.0 V
PESD5Z12 - - 12.0 V
Cddiode capacitance f = 1 MHz; VR=0V
PESD5Z2.5 - 229 300 pF
PESD5Z3.3 - 172 200 pF
PESD5Z5.0 - 89 150 pF
PESD5Z6.0 - 78 150 pF
PESD5Z7.0 - 69 150 pF
PESD5Z12 - 35 75 pF
Table 3. Pinning
Pin Description Simplified outline Symbol
1 cathode [1]
2 anode 21
006aaa152
2
1
Table 4. Ordering information
Type number Package
Name Description Version
PESD5Z2.5 SC-79 plastic surface-mounted package; 2 leads SOD523
PESD5Z3.3
PESD5Z5.0
PESD5Z6.0
PESD5Z7.0
PESD5Z12
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 3 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
4. Marking
5. Limiting values
[1] Non-repetitive current pulse 8/20 µs exponential decay waveform according to IEC 61000-4-5.
[2] Measured from pin 1 to 2.
Table 5. Marking codes
Type number Marking code
PESD5Z2.5 N7
PESD5Z3.3 N8
PESD5Z5.0 N9
PESD5Z6.0 NA
PESD5Z7.0 NB
PESD5Z12 NC
Table 6. Limiting values
In accordance with the Absolute Maximum Rating System (IEC 60134).
Symbol Parameter Conditions Min Max Unit
Per diode
PPP peak pulse power tp= 8/20 µs[1][2]
PESD5Z2.5 - 260 W
PESD5Z3.3 - 260 W
PESD5Z5.0 - 180 W
PESD5Z6.0 - 180 W
PESD5Z7.0 - 180 W
PESD5Z12 - 200 W
IPP peak pulse current tp= 8/20 µs[1][2]
PESD5Z2.5 - 20 A
PESD5Z3.3 - 20 A
PESD5Z5.0 - 10 A
PESD5Z6.0 - 10 A
PESD5Z7.0 - 10 A
PESD5Z12 - 6 A
Per device
Tjjunction temperature - 150 °C
Tamb ambient temperature 65 +150 °C
Tstg storage temperature 65 +150 °C
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 4 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
[1] Device stressed with ten non-repetitive ESD pulses.
[2] Measured from pin 1 to 2.
Table 7. ESD maximum ratings
Symbol Parameter Conditions Min Max Unit
Per diode
VESD electrostatic discharge voltage
PESD5Zx series IEC 61000-4-2
(contact discharge) [1][2] -30kV
machine model - 400 V
MIL-STD-883 (human
body model) -10kV
Table 8. ESD standards compliance
Standard Conditions
Per diode
IEC 61000-4-2; level 4 (ESD) > 15 kV (air); > 8 kV (contact)
MIL-STD-883; class 3 (human body model) > 4 kV
Fig 1. 8/20 µs pulse waveform according to
IEC 61000-4-5 Fig 2. ESD pulse waveform according to
IEC 61000-4-2
t (µs)
0403010 20
001aaa630
40
80
120
IPP
(%)
0
et
100 % IPP; 8 µs
50 % IPP; 20 µs
001aaa631
IPP
100 %
90 %
t
30 ns 60 ns
10 %
tr = 0.7 ns to 1 ns
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 5 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
6. Characteristics
Table 9. Characteristics
T
amb
=25
°
C unless otherwise specified.
Symbol Parameter Conditions Min Typ Max Unit
Per diode
VRWM reverse standoff voltage
PESD5Z2.5 - - 2.5 V
PESD5Z3.3 - - 3.3 V
PESD5Z5.0 - - 5.0 V
PESD5Z6.0 - - 6.0 V
PESD5Z7.0 - - 7.0 V
PESD5Z12 - - 12.0 V
IRM reverse leakage current
PESD5Z2.5 VRWM = 2.5 V - 0.5 6 µA
PESD5Z3.3 VRWM = 3.3 V - 8 50 nA
PESD5Z5.0 VRWM = 5.0 V - 5 50 nA
PESD5Z6.0 VRWM = 6.0 V - 2 10 nA
PESD5Z7.0 VRWM = 7.0 V - < 1 10 nA
PESD5Z12 VRWM = 12.0 V - < 1 10 nA
VBR breakdown voltage IR=1mA
PESD5Z2.5 4 - - V
PESD5Z3.3 5 - - V
PESD5Z5.0 6.2 - - V
PESD5Z6.0 6.8 - - V
PESD5Z7.0 7.5 - - V
PESD5Z12 14.1 - - V
Cddiode capacitance f = 1 MHz; VR=0V
PESD5Z2.5 - 229 300 pF
PESD5Z3.3 - 172 200 pF
PESD5Z5.0 - 89 150 pF
PESD5Z6.0 - 78 150 pF
PESD5Z7.0 - 69 150 pF
PESD5Z12 - 35 75 pF
VCL clamping voltage IPP =5A [1][2]
PESD5Z2.5 - 8 9 V
PESD5Z3.3 - 8 10 V
PESD5Z5.0 - 12 13 V
PESD5Z6.0 - 12 13 V
PESD5Z7.0 - 14 15 V
PESD5Z12 - 27 30 V
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 6 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
[1] Non-repetitive current pulse 8/20 µs exponential decay waveform according to IEC 61000-4-5.
[2] Measured from pin 1 to 2.
VCL clamping voltage [1][2]
PESD5Z2.5 IPP =20A --15V
PESD5Z3.3 IPP =20A --18V
PESD5Z5.0 IPP =10A --18V
PESD5Z6.0 IPP =10A --18V
PESD5Z7.0 IPP =10A --19V
PESD5Z12 IPP =6A --35V
rdif differential resistance IR=5mA
PESD5Z2.5 - - 60
PESD5Z3.3 - - 10
PESD5Z5.0 - - 15
PESD5Z6.0 - - 15
PESD5Z7.0 - - 15
PESD5Z12 - - 40
Table 9. Characteristics
…continued
T
amb
=25
°
C unless otherwise specified.
Symbol Parameter Conditions Min Typ Max Unit
Tamb =25°C
(1) PESD5Z2.5; PESD5Z3.3
(2) PESD5Z5.0; PESD5Z6.0; PESD5Z7.0; PESD5Z12
Fig 3. Peak pulse power as a function of exponential
pulse duration; typical values Fig 4. Relative variation of peak pulse power as a
function of junction temperature; typical values
006aab056
tp (µs)
110
4
103
10 102
10
102
103
104
PPP
(W)
1
(1)
(2)
Tj (°C)
0 20015050 100
001aaa193
0.4
0.8
1.2
PPP
0
PPP(25°C)
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 7 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
f = 1 MHz; Tamb =25°C
(1) PESD5Z2.5
(2) PESD5Z3.3
(3) PESD5Z5.0
f = 1 MHz; Tamb =25°C
(1) PESD5Z6.0
(2) PESD5Z7.0
(3) PESD5Z12
Fig 5. Diode capacitance as a function of reverse
voltage; typical values Fig 6. Diode capacitance as a function of reverse
voltage; typical values
PESD5Z2.5; VRWM = 2.5 V
PESD5Z3.3; VRWM = 3.3 V
IR is less than 50 nA at 150 °C for:
PESD5Z5.0; VRWM = 5.0 V
PESD5Z6.0; VRWM = 6.0 V
PESD5Z7.0; VRWM = 7.0 V
PESD5Z12; VRWM = 12.0 V
Fig 7. Relative variation of reverse current as a
function of junction temperature; typical values Fig 8. V-I characteristics for a unidirectional
ESD protection diode
VR (V)
054231
006aab057
100
150
50
200
250
Cd
(pF)
0
(1)
(2)
(3)
006aab058
VR (V)
01284
40
60
20
80
100
Cd
(pF)
0
(1)
(2)
(3)
006aab059
1
10
IR
IR(25°C)
101
Tj (°C)
100 15010005050
006aaa407
VCL VBR VRWM IRM
IR
IPP
V
I
P-N
+
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 8 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
Fig 9. ESD clamping test setup and waveforms for PESD5Z2.5
006aab060
50
RZ
CZDUT
(DEVICE
UNDER
TEST)
GND
450 RG 223/U
50 coax
ESD TESTER
acc. to IEC 61000-4-2
CZ = 150 pF; RZ = 330
4 GHz DIGITAL
OSCILLOSCOPE
10×
ATTENUATOR
GND
unclamped +8 kV ESD pulse waveform
(IEC 61000-4-2 network)
clamped 8 kV ESD pulse waveform
(IEC 61000-4-2 network)
vertical scale = 10 A/div
horizontal scale = 15 ns/div
vertical scale = 20 V/div
horizontal scale = 100 ns/div
GND
unclamped 8 kV ESD pulse waveform
(IEC 61000-4-2 network)
vertical scale = 10 A/div
horizontal scale = 15 ns/div
GND
clamped +8 kV ESD pulse waveform
(IEC 61000-4-2 network)
vertical scale = 20 V/div
horizontal scale = 100 ns/div
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 9 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
Fig 10. PESD5Z3.3: Clamped +8 kV ESD pulse
waveform (IEC 61000-4-2 network) Fig 11. PESD5Z3.3: Clamped 8 kV ESD pulse
waveform (IEC 61000-4-2 network)
Fig 12. PESD5Z5.0: Clamped +8 kV ESD pulse
waveform (IEC 61000-4-2 network) Fig 13. PESD5Z5.0: Clamped 8 kV ESD pulse
waveform (IEC 61000-4-2 network)
006aab061
vertical scale = 20 V/div
horizontal scale = 100 ns/div
GND
006aab062
vertical scale = 20 V/div
horizontal scale = 100 ns/div
GND
006aab063
vertical scale = 20 V/div
horizontal scale = 100 ns/div
GND
006aab064
vertical scale = 20 V/div
horizontal scale = 100 ns/div
GND
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 10 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
Fig 14. PESD5Z6.0: Clamped +8 kV ESD pulse
waveform (IEC 61000-4-2 network) Fig 15. PESD5Z6.0: Clamped 8 kV ESD pulse
waveform (IEC 61000-4-2 network)
Fig 16. PESD5Z7.0: Clamped +8 kV ESD pulse
waveform (IEC 61000-4-2 network) Fig 17. PESD5Z7.0: Clamped 8 kV ESD pulse
waveform (IEC 61000-4-2 network)
006aab065
vertical scale = 20 V/div
horizontal scale = 100 ns/div
GND
006aab066
vertical scale = 20 V/div
horizontal scale = 100 ns/div
GND
006aab067
vertical scale = 20 V/div
horizontal scale = 100 ns/div
GND
006aab068
vertical scale = 20 V/div
horizontal scale = 100 ns/div
GND
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 11 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
Fig 18. PESD5Z12: Clamped +8 kV ESD pulse
waveform (IEC 61000-4-2 network) Fig 19. PESD5Z12: Clamped 8 kV ESD pulse
waveform (IEC 61000-4-2 network)
006aab069
vertical scale = 20 V/div
horizontal scale = 100 ns/div
GND
006aab070
vertical scale = 20 V/div
horizontal scale = 100 ns/div
GND
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 12 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
7. Application information
The PESD5Zx series is designed for the protection of one unidirectional data or signal line
from the damage caused by ESD and surge pulses. The device may be used on lines
where the signal polarities are either positive or negative with respect to ground. The
PESD5Zx series provides a surge capability of 260 W per line for an 8/20 µs waveform.
Circuit board layout and protection device placement
Circuit board layout is critical for the suppression of ESD, Electrical Fast Transient (EFT)
and surge transients. The following guidelines are recommended:
1. Place the PESD5Zx as close to the input terminal or connector as possible.
2. The path length between the PESD5Zx and the protected line should be minimized.
3. Keep parallel signal paths to a minimum.
4. Avoid running protected conductors in parallel with unprotected conductors.
5. Minimize all Printed-Circuit Board (PCB) conductive loops including power and
ground loops.
6. Minimize the length of the transient return path to ground.
7. Avoid using shared transient return paths to a common ground point.
8. Ground planes should be used whenever possible. For multilayer PCBs, use ground
vias.
Fig 20. Application diagram
006aab071
ground
line to be protected
(positive signal polarity)
PESD5Zx
unidirectional protection of one line
ground
line to be protected
(negative signal polarity)
PESD5Zx
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 13 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
8. Package outline
9. Packing information
[1] For further information and the availability of packing methods, see Section 13.
Fig 21. Package outline SOD523 (SC-79)
02-12-13Dimensions in mm
1.65
1.55 1.25
1.15
0.17
0.11
0.34
0.26
0.65
0.58
0.85
0.75
1
2
Table 10. Packing methods
The indicated -xxx are the last three digits of the 12NC ordering code.
[1]
Type number Package Description Packing quantity
3000 8000 10000
PESD5Z2.5 SOD523 2 mm pitch, 8 mm tape and reel - -315 -
4 mm pitch, 8 mm tape and reel -115 - -135
PESD5Z3.3 SOD523 2 mm pitch, 8 mm tape and reel - -315 -
4 mm pitch, 8 mm tape and reel -115 - -135
PESD5Z5.0 SOD523 2 mm pitch, 8 mm tape and reel - -315 -
4 mm pitch, 8 mm tape and reel -115 - -135
PESD5Z6.0 SOD523 2 mm pitch, 8 mm tape and reel - -315 -
4 mm pitch, 8 mm tape and reel -115 - -135
PESD5Z7.0 SOD523 2 mm pitch, 8 mm tape and reel - -315 -
4 mm pitch, 8 mm tape and reel -115 - -135
PESD5Z12 SOD523 2 mm pitch, 8 mm tape and reel - -315 -
4 mm pitch, 8 mm tape and reel -115 - -135
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 14 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
10. Soldering
Reflow soldering is the only recommended soldering method.
Dimensions in mm
Fig 22. Reflow soldering footprint SOD523 (SC-79)
mgs343
1.80
1.90
0.30
0.40
0.50
1.20 0.60
2.15
solder lands
solder resist
occupied area
solder paste
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 15 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
11. Revision history
Table 11. Revision history
Document ID Release date Data sheet status Change notice Supersedes
PESD5ZX_SER_2 20080404 Product data sheet - PESD5ZX_SER_1
Modifications: Table 10: Type number updated to PESD5Z12
PESD5ZX_SER_1 20070813 Product data sheet - -
PESD5ZX_SER_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 4 April 2008 16 of 17
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
12. Legal information
12.1 Data sheet status
[1] Please consult the most recently issued document before initiating or completing a design.
[2] The term ‘short data sheet’ is explained in section “Definitions”.
[3] The product status of device(s) described in this document may have changed since this document was published and may differ in case of multiple devices. The latest product status
information is available on the Internet at URL http://www.nxp.com.
12.2 Definitions
Draft — The document is a draft version only. The content is still under
internal review and subject to formal approval, which may result in
modifications or additions. NXP Semiconductors does not give any
representations or warranties as to the accuracy or completeness of
information included herein and shall have no liability for the consequences of
use of such information.
Short data sheet — A short data sheet is an extract from a full data sheet
with the same product type number(s) and title. A short data sheet is intended
for quick reference only and should not be relied upon to contain detailed and
full information. For detailed and full information see the relevant full data
sheet, which is available on request via the local NXP Semiconductors sales
office. In case of any inconsistency or conflict with the short data sheet, the
full data sheet shall prevail.
12.3 Disclaimers
General — Information in this document is believed to be accurate and
reliable. However, NXP Semiconductors does not give any representations or
warranties, expressed or implied, as to the accuracy or completeness of such
information and shall have no liability for the consequences of use of such
information.
Right to make changes — NXP Semiconductors reserves the right to make
changes to information published in this document, including without
limitation specifications and product descriptions, at any time and without
notice. This document supersedes and replaces all information supplied prior
to the publication hereof.
Suitability for use — NXP Semiconductors products are not designed,
authorized or warranted to be suitable for use in medical, military, aircraft,
space or life support equipment, nor in applications where failure or
malfunction of an NXP Semiconductors product can reasonably be expected
to result in personal injury, death or severe property or environmental
damage. NXP Semiconductors accepts no liability for inclusion and/or use of
NXP Semiconductors products in such equipment or applications and
therefore such inclusion and/or use is at the customer’s own risk.
Applications — Applications that are described herein for any of these
products are for illustrative purposes only. NXP Semiconductors makes no
representation or warranty that such applications will be suitable for the
specified use without further testing or modification.
Limiting values — Stress above one or more limiting values (as defined in
the Absolute Maximum Ratings System of IEC 60134) may cause permanent
damage to the device. Limiting values are stress ratings only and operation of
the device at these or any other conditions above those given in the
Characteristics sections of this document is not implied. Exposure to limiting
values for extended periods may affect device reliability.
Terms and conditions of sale — NXP Semiconductors products are sold
subject to the general terms and conditions of commercial sale, as published
at http://www.nxp.com/profile/terms, including those pertaining to warranty,
intellectual property rights infringement and limitation of liability, unless
explicitly otherwise agreed to in writing by NXP Semiconductors. In case of
any inconsistency or conflict between information in this document and such
terms and conditions, the latter will prevail.
No offer to sell or license — Nothing in this document may be interpreted
or construed as an offer to sell products that is open for acceptance or the
grant, conveyance or implication of any license under any copyrights, patents
or other industrial or intellectual property rights.
12.4 Trademarks
Notice: All referenced brands, product names, service names and trademarks
are the property of their respective owners.
13. Contact information
For additional information, please visit: http://www.nxp.com
For sales office addresses, send an email to: salesaddresses@nxp.com
Document status[1][2] Product status[3] Definition
Objective [short] data sheet Development This document contains data from the objective specification for product development.
Preliminary [short] data sheet Qualification This document contains data from the preliminary specification.
Product [short] data sheet Production This document contains the product specification.
NXP Semiconductors PESD5Zx series
Low capacitance unidirectional ESD protection diodes
© NXP B.V. 2008. All rights reserved.
For more information, please visit: http://www.nxp.com
For sales office addresses, please send an email to: salesaddresses@nxp.com
Date of release: 4 April 2008
Document identifier: PESD5ZX_SER_2
Please be aware that important notices concerning this document and the product(s)
described herein, have been included in section ‘Legal information’.
14. Contents
1 Product profile . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 General description. . . . . . . . . . . . . . . . . . . . . . 1
1.2 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.4 Quick reference data. . . . . . . . . . . . . . . . . . . . . 2
2 Pinning information. . . . . . . . . . . . . . . . . . . . . . 2
3 Ordering information. . . . . . . . . . . . . . . . . . . . . 2
4 Marking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5 Limiting values. . . . . . . . . . . . . . . . . . . . . . . . . . 3
6 Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . 5
7 Application information. . . . . . . . . . . . . . . . . . 12
8 Package outline . . . . . . . . . . . . . . . . . . . . . . . . 13
9 Packing information. . . . . . . . . . . . . . . . . . . . . 13
10 Soldering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
11 Revision history. . . . . . . . . . . . . . . . . . . . . . . . 15
12 Legal information. . . . . . . . . . . . . . . . . . . . . . . 16
12.1 Data sheet status . . . . . . . . . . . . . . . . . . . . . . 16
12.2 Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
12.3 Disclaimers. . . . . . . . . . . . . . . . . . . . . . . . . . . 16
12.4 Trademarks. . . . . . . . . . . . . . . . . . . . . . . . . . . 16
13 Contact information. . . . . . . . . . . . . . . . . . . . . 16
14 Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17