Telecom GDT Training
Training Agenda
1.
GDT Definition and Telecom Circuit Protection
2.
GDT Characteristics and Device Physics
3.
GDT Telecom Applications Protection Example
4.
GDT Telecom Applications Product Selection
5.
Littelfuse GDT Product Road Map
6.
Telecom GDT Technology Challenges
Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved.
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Telecom GDT Training
Section 1 GDT Definition and Telecom Circuit Protection
GDT Definition
–
A Gas Discharge Tube (GDT) is a gas discharge plasma device that provides a crowbar
current path to protect electronic components from transient threat.
Circuit Protection Concepts
–
Potential safety threats that requires circuit protection
•
Protect against environment threats such as Lightning, EFT Surges, and ESD
–
Regulatory requirements related to circuit protection
•
IEC Regulations
•
UL Regulations
•
Other Regulations
–
Method of circuit protection
•
Over voltage
•
Voltage transient
–
Added value of circuit protection
•
Prevent disaster such as fire
•
Avoid law suit and warranty issues
Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved.
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Telecom GDT Training
Gas Discharge Tubes
V
Ignition Voltage (Overshoot)
Working
Voltage
t
Advantages
Disadvantages
• Inherently bidirectional
• Low capacitance
• Ability to handle high surge
currents (>20kA)
• Very low impedance following
spark over
• Poor initial “let through voltage” (overshoot)
• Slow response (compared to SIDACtor or PGB)
• May require series resistance to prevent
follow-on current
• Trigger voltage varies
• Degrades with repetitive transients
• Fails open circuit
Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved.
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GDT Definition and Telecom Circuit Protection
Circuit Protection Needs in Telecom Systems
– Thunderstorms around the world deliver 8 million lightning flashes every day. Peak current in
lightning discharges range from a few KA to many hundreds of KA. Induced currents from indirect
strikes range from 10A to 20KA.
–
ESD results from the build up of electrical charge, when two non-conductive materials are brought
together then separated. The potential between a human body & an object can exceed 35,000
volts. An ESD event can occur to the telecom system or portable devices through human contact
and usage of the telecom devices.
–
Inductive Load Switching is caused when an inductive load is interrupted. It occurs in
factory/industrial environments where motors and relays (inductive loads) are turned on and off.
–
Short Circuit or Power Cross events can occur due to human error (such cutting a phone and power
line simultaneously during construction) or natural disaster such as hurricane, thunderstorm.
–
One or a combination of the above threats can have obvious adverse effects on semiconductor/IC
devices, electro-mechanical contacts, wiring insulation, etc., to cause interruption of telecom
equipment operation, telephone service, and even fire.
Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved.
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GDT Definition and Telecom Circuit Protection
GDT Technology for Telecom Overvoltage Circuit Protection
Telecom equipment should be protected from overvoltage conditions using GDTs, MOVs, or
silicon devices such as SIDACtors or TVS diodes.
Gas Discharge Tubes / Surge Arresters are mostly used for Primary Protection against transients
caused by lightning.
Secondary Protection applications traditionally have used Silicon solutions but due to the
increased bandwidth now required by telephone lines the GDT has the benefit of having
significantly lower capacitance levels and are now competing with Silicon solutions due to their
relatively high capacitance.
Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved.
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Telecom GDT Training
Section 2
GDT Characteristics and Device Physics
•
Basic GDT Characteristics
–
Electrical Characteristics
•
V-I curve characteristics
•
Trigger voltage
•
Clamping voltage
•
Response time
•
Leakage current
•
GDT Construction and how it affects the related GDT characteristics
–
GDT structure vs. electrical characteristics
–
GDT structure vs. maximum ratings
–
GDT de-rating
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GDT Characteristics and Device Physics
Electrical GDT Characteristics
VH (holdover voltage) is the key
parameter. With the exception of 75V
and 90V devices that have a holdover
voltage of 50V, all other devices have a
holdover voltage of 135V which will not
cause latch up for the telecom system.
VSDC (DC breakover voltage) is
measured at a slow rate of rise, usually
100V/sec. This is to make sure that the
lower DC breakover voltage is above
the system voltage.
VS (dynamic breakover voltage)
determines the level of protection
clamping voltage.
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GDT Characteristics and Device Physics
GDT Construction
The gas plasma arrester operates as a
voltage dependent switch. When the spark
over voltage applies across the device
greater than its breakdown voltage, an arc
discharge takes place within the tube.
A gas plasma device can typically handle
5kA to 20kA current.
The performance of the GDT can be
determined by the following factors:
- Electrode material, shape and surface
finish.
- Electrode coatings/activation, electron work
function, and Electrode spacing.
- Gas volume and pressure, temperature
Type of gas, and ionization energy of the
gas.
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Telecom GDT Training
Section 3
GDT Telecom Applications Protection Examples
•Exchange Equipment
•Main Distribution Frame
•Subscriber Terminal
•Telephones
•Fax Machines
•Modems
•Base Stations for Cell Phones
•Multiplexers
•LAN Network Terminals
•Amplifiers
•ADSL/VDSL/HDSL Equipment
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GDT Telecom Applications Protection Examples
Telecom 3 Point Protection Solution (typically employed in outside plant protectors)
All outside plant protectors perform a Primary Protection function, meaning they act as the first
line of defense. The Gas Plasma device, because of it’s high energy capability (up to 20KA),
is ideal for these applications. Typically, 5KA would be the lowest rating for a Primary
Protector used in an outside plant application.
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GDT Telecom Applications Protection Examples
Telecom 3 Point Protection Solution (typically employed in outside plant protectors)
3 Terminal GDT
2 x 2 Terminal GDT
Three terminal Gas Plasma devices are constructed using a common gas
chamber, so in differential mode (a transient appearing on both Tip and Ring) the
resulting differential transient is smaller.
Two terminal tubes are often easier, from a mechanical standpoint, to incorporate
in module designs.
Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved.
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GDT Telecom Applications Protection Examples
MDF Protection Modules
MDF modules perform some level of Primary Protection, but often incorporate
secondary level features as well. Such devices are are of Hybrid construction
incorporating more than one technology.
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GDT Telecom Applications Protection Examples
Telecom 5 Point Protection Solution (Hybrid design commonly deployed in MDF modules)
Depending on geography, the level of primary protection provided in the MDF varies. In
certain regions of the world the effects of lightning can be more severe. In these cases,
the MDF module will need a surge rating of several thousand Amperes (KA); the solution
here is to use a Gas Plasma device. A typical rating in this application is 5KA.
Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved.
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GDT Telecom Applications Protection Examples
3 Terminal Device (to provide protection against isolation breakdown on transformer)
In order to transfer high speed data over distance and without loss or corruption, the
protector has a exhibit low ‘insertion loss’ values (normally measured in dB). To some
extent, the capacitance value has a direct relationship with insertion loss: higher
capacitance = higher insertion loss.
Littelfuse “broadband optimized” protectors offer very low insertion loss, even up to 1.8Ghz,
making them virtually transparent to the protected system.
Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved.
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GDT Telecom Applications Protection Examples
Global Lab Capabilities
•
•
•
•
Qualification of all LF products
UL-Approved Customer Testing in ISO 17025 Lab (Des Plaines)
– High power (AC/DC up to 1KV/50KA) UL approvals available in DP
– Telcordia approvals in DP planned (2008)
Verification of Telcordia, ITU, IEC, FCC, and other industry, regulatory, and safety standards
– Verification to various OC and OV standards
• Insure application meets standards before submitting for approval
Customer Application testing
– Assistance with design-in and performance verification
• Help with selection of appropriate technology and rating
– Application troubleshooting
• Assistance insuring proper OV/OC and primary/secondary protection coordination
– Competitive evaluations
• Competitive or technology performance comparisons
– Reliability & Tin Whisker data/testing
Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved.
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Telecom GDT Training
Section 4
GDT Telecom Applications Product Selection
GDT Product Selection
–
Select power rating: 5A/5KA, 10A/10KA or 20A/20KA
–
Select package outline: 2 Pole, 3 Pole, Axial, Radial or SM
–
Choose a device with a minimum DC Breakdown higher than the maximum system voltage
–
Select the corresponding device voltage type
Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved.
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GDT Telecom Applications Product Selection
Overvoltage Protection Comparison
Technology
GDT
GDTs
MOV
TVS
Response Time
Fastest
Slowest
Slower
response time
Fast
Capacitance
Low
As low as 1pF
High
Higher
Current
surge rating
High
As high as 500A
for 200 impulses
High
Low
Electrical
Characteristic
Stable
Degrade with time
Fatigue after
multiple
pulses
Stable
Application
Principle Overvoltage
in telecom, datacom
circuit
Telecom
application
Useful in AC
applications
Secondary Protectors
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GDT Telecom Applications Product Selection
Characteristics of Transient Voltage Suppressor Technology
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GDT Telecom Applications Product Selection
GDT Selection
Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved.
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Telecom GDT Training
Section 5 Littelfuse GDT Product Road Map
Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved.
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Telecom GDT Training
Section 6 Telecom GDT Technology Challenges
–
Higher Surge Rating and Smaller Packaging
–
Multiple Elements in One Package
–
GDT Technology Combined with Other Technologies in Same Package
–
Improved De-rating Characteristics
Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved.
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