The ABCs of Littelfuse Multilayer Suppressors By Littelfuse

The ABCs of Littelfuse Multilayer Suppressors By Littelfuse
The ABCs of Littelfuse Multilayer Suppressors
A pplication Note
J u ly 1 9 9 9
AN9671.2
Author: Don Tidey
Introduction
• Medical equipment such as electronic diagnostic
instruments, monitors and recorders
This guide is similar to “The ABCs of MOVs”, offering
specific information on Multilayer suppressor device
technology and is intended to be a supplement to the
Littelfuse Multilayer data sheets.
• Power supplies
“A” is for Applications, giving general examples of where
these products are used.
• Microprocessor-based controls for machinery and
robotics
“B” is for Basics, describing the fundamental fabrication,
operation and functions.
• Opto isolator
“C” is for Common Questions, addressing frequently asked
questions from Production Engineers, and Designers.
• Portable/hand-held industrial instruments
There are a number of sources from which literature may be
received. To learn more about Multilayer Suppressors:
• Consumer electronics
• Call Littelfuse, Inc. at 1-800-999-9445 in the U.S.
(1-847-824-1188 outside the U.S.)
• Visit the Internet at www.littelfuse.com
Applications
As with MOVs, Littelfuse Multilayer Suppressors protect a
broad range of applications and circuit components. They
are offered in different designs to accommodate different
suppression requirements. For an initial determination of
which type is suitable, it is desirable to know:
1. The working voltage or maximum system voltage.
2. The type of transient that is to be suppressed and its
energy level.
3. What circuit or component requires protection and,
therefore, to what level must the transient be suppressed.
Multilayer Suppressors are most often applied to low voltage
(<50VDC) systems on power supply, signal, or control lines in
order to suppress ESD, EFT, Surge, or other transients at the
circuit board level for component protection. Additionally, these
devices may be applied to products subjected to immunity
testing such as the EN61000 (IEC) standards in order to
achieve specific electromagnetic compatibility (EMC) ratings.
The products and circuits to which these Multilayer
Suppressors are applicable are diverse and include:
• Computers and their associated peripheral devices
including I/O interfaces
• Office equipment such as keypad/controllers for
copiers, facsimile and printers
• Automotive electronic modules
10-67
• Communication devices including MODEMs, wireless
LANs, Cellular phones/Cordless phones, Pagers
• Sensors
• LASER diode devices
Basics
Q. What is a Multilayer Suppressor?
A. A Littelfuse Multilayer Suppressor is one of a family of
transient voltage suppression devices. They bear
similarity to Metal Oxide Varistors in that they are
voltage dependent, nonlinear devices that exhibit a
bidirectional clamping characteristic and are based on
a Zinc Oxide material technology. They are designed to
suppress transients at the circuit board level in order to
protect components and circuit functions by clamping
the transient and dissipating its energy within the
suppressor. These devices are ceramic and
manufactured in leadless, surface mount form.
Q. What are the Device Families?
A. Since voltage transients have numerous sources and
characteristics, Littelfuse Multilayer Suppressors are
offered in three separate Series.
The “ML” Series (data sheet #2461) supports the
broadest range of applications with operating voltages
from 3.5 to 120VDC and sizes of “0603”, “0805”, “1206”,
and “1210”. This Series offers high peak current (8x20)
ratings and is designed for board-level Surge, EFT, ESD
and other specific transient events.
The “AUML” Series (data sheet #3387) is specifically
characterized for Automotive-related parameters and
transients. This Series has the single, 18VDC working
voltage in sizes of “1210”, “1812”, and “2220”, and
affords module protection from secondary Load Dump
and other transients found in the auto environment.
The “MLE” Series (data sheet #4263) is designed for
lower energy transients and is rated for ESD
suppression in order to protect sensitive components
and, like the “ML”, helps products meet Electromagnetic
Compatibility test immunity standards. This Series is
also specifically characterized for capacitance and
1-800-999-9445 or 1-847-824-1188 | Copyright
© Littelfuse, Inc. 1999
Application Note 9671
impedance for combined suppressor / high frequency
attenuation applications. MLE devices may be applied
to circuits with a working voltage up to 18VDC and are
offered in “0603”, “0805”, and “1206” sizes. The MLN
device (data sheet #4682) is a four-section Multilayer
array in the 1206 leadless chip size and thereby offers
the designer reduced part count and space savings on
circuit cards. The standard MLN may be operated at
any voltage up to 18VDC and is primarily intended for
the suppression of ESD or other low-energy transients.
The “MLN” device (data sheet #4682) is a four section
Multilayer array in the 1206 leadless chip size and
thereby offers the designer reduced part count and
space savings on circuit cards. The standard MLN may
be operated at any voltage up to 10VDC and is primarily
intended for the suppression of ESD or other low energy
transients.
Q. How Are These Devices Fabricated?
A. Each of the three Series is fabricated by interleaving
layers of a specific semiconducting dielectric material
and metal electrodes which are alternately screened
onto a substrate. The number of layers built and the
dielectric material and thickness varies with the device
type. This substrate is then divided into the individual
devices which are sintered or “fired”, forming a
homogenous ceramic device. Metal end terminations
are then applied and also fired, completing the basic
operation.
Common Questions
Q. Is There Any Difference Between the ML, AUML,
MLN and MLE Series?
A. Yes. Generically they are the same, but they can differ
from each other in terms of dielectric material
formulation, layer count, sizes offered, electrical
characterization/parameters, and ratings.
Q. Can Custom Voltage Parts Be Made for My
Particular Application?
Q. What Standard End Termination Materials are
Used?
A. The standard termination is a fired-on Silver/Platinum
alloy. An optional Silver/Palladium is also available. To
designate either, a character in the model number is
added or deleted as shown in the associated data sheet
under ordering information.
Q. Why are Different End Terminations Offered?
A. In order to best match specific soldering
operations/requirements. Generally, the standard
Silver/Platinum finish is used for reflow methods. The
optional Silver/Palladium finish is recommended for wave
solder methods in order to improve leach resistance.
Q. Does Littelfuse Have a Recommended Solder
Procedure?
A. Littelfuse Multilayer devices are compatible with typical
industry standard reflow and solder wave methods.
Specific solder profile recommendations can be found in
the data sheets.
Q. What is the Capacitance of Multilayers?
A. Generally speaking, the range of capacitance for
Multilayers is from less than 100 Picofarads to a few
thousand Picofarads and inversely proportional to the
working voltage. Dielectric type and thickness, number of
layers, and device size all contribute in determining the
capacitance. Capacitance, therefore, can be tailored by
changing these variables.
Q. How Do the Multilayer Series Differ From the
Littelfuse CH Series?
A. The CH Series is fabricated from a single layer of MOV
material. It is supplied in a single, larger chip size of
5mm x 8mm (3220) and has a higher voltage range up to
369VDC.
Q. Can the Littelfuse ML Series Replace a Zener?
A. Littelfuse Multilayers are often used to replace TVSS
Zener diodes. Because the technologies and form
factors differ, a direct cross reference is not practical.
Contact Littelfuse to help compare parameters and
determine if a Multilayer can be used in the application.
A. Yes. Littelfuse can tailor the voltage rating of Multilayers
by changing the dielectric material and/or thickness
during fabrication. Also, by changing layer count,
parameters such as Capacitance and Energy ratings
can also be modified.
Q. Do Multilayers Provide Bidirectional Clamping
Like MOVs?
Q. How is the High Peak Surge Current Rating
Achieved?
A. Yes. Multilayers provide suppression of transients of
either polarity.
A. The internal, interleaved dielectric/electrode layers form
essentially parallel devices so the effective surface area
is much larger than the Multilayer size would suggest.
Q. Are Multilayer Suppressors 100% Tested?
Q. Is There Any Plastic Used to Form the
Package?
A. The ceramic construction forms the device itself. There is
no encapsulation, plastic or otherwise, used in these
devices.
10-68
A. Yes. All Multilayer Suppressors receive a final 100%
electrical test for Nominal Voltage and Leakage at the
Tape and Reel packaging operation.
Application Note 9671
Q. What Information is Contained in the ML or
MLE Model Number Sequence?
A. Using the V18MLA0805L as an example:
V
The Multilayer maintains the Littelfuse MOV “V”
(Varistor) designation for Transient Suppressors.
18
The maximum DC working voltage
ML
The Multilayer Series
A
Performance or application designator
0805
The EIA size for length and width. (80mils x
50mils in this case)
L
Low Capacitance version (reduced layer count
version in this case)
Q. Will This Part Number Vary When Placing An
Order?
A. Yes. A suffix is added to identify the desired packaging
(bulk or reeled) or end termination options. See the
Littelfuse data sheet for instructions. Additionally, a
custom part will have an X suffix followed by a unique 4
digit designation.
Q. What is the Procedure in Selecting a
Multilayer?
A. The basic procedure is to:
1. Determine the working voltage of the circuit in which the
ML is to be placed and select an ML with equal or
greater V(DC) MAX.
2. Determine what transient needs to be suppressed in
terms of its type, peak surge current and energy in order
to select the appropriate Series and device size.
Q. Why is the MLE Characterized for Impedance?
A. While operating in their normal standby mode, the
inherent capacitance of all MLs help attenuate unwanted
noise signals or harmonic frequencies. The MLE is
additionally characterized for impedance since the low
voltage circuits to which this Series is intended for use
may be particularly sensitive to noise or require filtering
of power supply lines, for example.
Q. Is Clamping Performance Derated Over
Temperature for Multilayers?
A. No. Clamping voltage, peak current and energy are not
derated over the entire temperature range, -55oC to
125oC ambient.
Q. Are These Devices Marked or Branded?
A. No. At the present time part designation is identified on
packaging/shipping labels, including bar coding, where
applicable.
Q. Where can Multilayers Typically be Placed in
Circuits?
A. As a Clamping-Type Suppressor, the Multilayer is usually
placed between the circuit point subject to transients and
the reference electrical “Ground” or “Common”, as close
as practical to the transient source. Board level
connections include:
• Across Switching Transistors
• Across Inductive Loads such as Relays or Solenoids
• On Local DC Power Supply Lines, Replacing Zener or
Zener/Capacitor Combinations
• The Data Lines or Control Lines of ICs to Ground
• Across Remote Sensors
3. Determine the maximum acceptable clamping voltage
(or sensitivity level) of the components to be protected
and review the V-I characteristics curves of the particular
ML.
• On High Side or Low Side Drivers
4. Other things to consider are the bidirectional clamping
and typical capacitance of the ML.
• Op Amp Input or Output Terminals to Ground
Q. Are The Multilayers Subject To Listing By Safety
Organizations?
A. Since the intended usage is in low voltage applications
and not AC line or high voltage circuits, no listings are
required. Likewise, since these devices are ceramic and
not plastic, flammability ratings are not applicable.
Q. What ESD Level is the MLE Rated For?
A. The MLE is rated to the highest ESD voltage level
categories of the IEC-1000-4-2 (human body model)
specification. These are the 15kV (air discharge) and the
8kV (direct contact) methods. The IEC specification is a
test method used to determine a given level of ESD
immunity for EMC (Electromagnetic Compatibility)
ratings of end products or systems. The MLE Series is
used to suppress this ESD transient, thereby allowing
products to meet EMC criteria.
10-69
• Bus Transceiver I/O Lines to Ground
• Across Laser Diodes
• Transistor Base or Gate Terminals to Ground
• On Interface Terminals or Connectors Subject to Human
Contact or Conducted Transients
Q: What is the Leakage of Each Channel of the
MLN Array at 5VDC?
A. The Maximum Leakage is less than 6nA for any one
channel.
Q. Can Transients be Applied to all Four Inputs of
the MLN Simultaneously?
A. The MLN array device exhibits excellent channel isolation
and will suppress simultaneous transients at each terminal
within its maximum current and energy ratings.
Q. I Have Two Lines to Protect. Can Littelfuse
Produce a Dual Version of the MLN Quad Device?
A. Yes. Contact the Sales department with your specific
requirements. Additionally, other parameters such as
Working Voltage and Capacitance can be custom tailored.
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