EC622A - ESD Suppression Technologies

ESD Suppression Technologies
Integrated circuits (IC’s) and application
specific integrated circuits (ASIC’s) are
manufactured with various levels of ESD
protection incorporated into the silicon die
itself.This protection circuitry is designed
onto the chip to maximize yields in the chip
foundry and in the board manufacturing
facility. Examples of these chips (which are
the “brains” of today’s electronic products)
include microprocessors, USB transceiver
chips, IEEE 1394 controllers, and video
graphics chips.The are used in a host of
devices such as computers (and peripherals), cell phones, PDA’s, flat panel LCD
displays, and network hardware.
The trade-off for the chip designer is ESD
protection versus die space. As more ESD
protection structures are incorporated into
the chip, its survivability is increased, but less
space is available for functional circuitry, or
the chip has to be made larger. In today’s
electronic equipment, the overriding philosophy is “smaller is better”. So a limited
amount of space will be sacrificed for ESD
The typical maximum level of ESD protection included in modern chips is 2,000 V.
While this is sufficient to improve survivability in the manufacturing process, much
higher ESD levels will be experienced when
the final product is put into use.The “base”
level of protection is sufficient because the
manufacturing environment requires the
use of ESD-minimizing treatments.
Humidity and ionization controls are used,
workspaces are grounded, and personnel
wear anti-static or static dissipative clothing.
However, once the end product (computer,
PDA, printer, etc.) is put into service, it will
be exposed to ESD levels higher than those
experienced in the manufacturing environment. Unless ESD is prevented from getting
onto the circuit, or supplemental protection
is added to circuit, the product can be
rendered useless due to interaction with
the user. Obviously this represents an issue
with respect to product reliability. The
“supplemental protection” includes the use
of ESD suppressors.
Figures 1 and 2 illustrate how the
ESD suppressors “re-routes” the
ESD transient so that the chip is not
Circuit Board
Data Lines
ESD Current
These technologies protect the circuit by
“clamping” the transient voltage to a safe
level, above the circuit operating voltage
(3.3, 6, 12VDC, etc.).The energy that would
have gone into the circuit (and caused
damage) is dissipated by the ESD suppressor and the source of the ESD.
Voltage (logV)
ESD Suppression
Energy that the circuitry would
have experienced
V line
Clamped Waveform
Time (s)
Figure 1. Electronic Device - ESD transient is conducted
directly into the chip via an unprotected data line
Circuit Board
Data Lines
Figure 3. ESD waveform
ESD Suppressor
Multilayer Varistors (MLVs)
ESD Current
Figure 2. Electronic Device - ESD suppressor clamps the
transient, thus limiting ESD current to the chip
ESD Suppression
Littelfuse offers three distinct product families that can be used for ESD suppression.
These include the electroceramic MLV
(MultiLayer Varistor), silicon (SP72x and
SP050x) and polymer-based PulseGuard®
suppressor products. Each family has attributes that differentiate it from the other
technologies, but, in general, they are all
effective solutions for ESD suppression.
These technologies will protect the sensitive circuitry against external threats (such
as user-generated ESD). Further, the MLV
and SP72x products can also protect
against system generated transients such as
EFT’s (Electrical Fast Transients) and surges
(switching transients and lightning).
Fired Ceramic
End Termination
Metal Inner Electrodes
Figure 4. Multilayer internal construction
The MLV products are manufactured by
interleaving metal electrodes and ZincOxide ceramic layers.The Zinc-Oxide
ceramic acts like an insulator during normal
circuit conditions. However, when the voltage is elevated (as in an ESD event), the
grain boundaries of the Zinc Oxide crystals
transition from high to low resistance to
shunt the transient from the protected line
to ground.
MLV’s are the most robust of the ESD
suppression technologies and can be used
to protect lines (power and communica-
tions) that have operating voltages of 3.5 to
120VDC (2.5 to 107VAC).They can also be
used to provide protection against Electrical
Fast Transients (EFT’s). Additionally, their
inherent capacitance (65-4,500 pF) can
provide filtering against high frequency
A new family of MLV products has been
added which addresses size and capacitance
issues. The MHS series is available in the
0402 package size and has capacitance
values of 3pF and 12pF. The MHS products
can be used where data speed is high (up
to roughly 125Mbps) and space is a prime
SP72x Series- SCR/Diode
SP05xx Series TVS
Avalanche Diode Arrays
Figure 6. SP05x Series TVS Avalanche Diode Arrays
The SP05xx products are comprised of
multiple TVS avalanche diodes (one diode is
highlighted in blue) that conduct the transient to the ground (V-) rail. Simply put, the
diodes function like a switch. Using channel
1 as an example, once the transient
exceeds the breakdown voltage of the
diode, the transient’s current is conducted
to the V- rail. At the same time, the voltage
of the transient is clamped to a low value.
PulseGuard suppressor products differ from
the MLV’s and SP72x’s in that they can only
be used for ESD protection.The polymer
material is not capable of withstanding the
higher energy levels of EFT’s and surge
transients. On the other hand, PulseGuard
products have the lowest capacitance (.050
pF) of the suppressor technologies and can
be used to protect communication lines
that operate at speeds up to 3-5 Gbps.
4 AND 6
Figure 5. SP72x functional block diagram
The SP72x products are comprised of
multiple SCR/Diode cells (one cell is highlighted in blue) that conducts the transient
to the power (V+) or ground (V-) rails.
Simply put, the cells functions like switches.
Using pin 1 as an example, once the transient exceeds the V+ voltage (pin 5) by
0.7V, the upper leg conducts to the V+ rail.
Likewise, once a negative transient falls
below the ground voltage by 0.7V, the
bottom leg will conduct to the V- rail (pin
2). In this manner, the transient is shunted
from the protected line (pins 1, 3, 4, and 6
in this example) to V+ or V-.
SP72x products are robust devices that can
protect communication lines from ESD, and
higher energy transients like Electrical Fast
Transients (EFT’s) and surge events.They
have low capacitance (3-5 pF) and can be
used to protect communication lines that
operate at high speeds (up to approximately
SP05xx products are available in a wide
variety of package styles and number of
lines of protection. Package options include
SOT-23, SOT-143,TSSOP, MSOP and chip
scale package (CSP).The number of lines of
protection range from one to eighteen with
capacitance values ranging from 3-39pF,
making them suitable for the protection of
data lines that operate at medium to high
speeds (roughly 100 Kbps to 125Mbps).
PulseGuard® Suppressor
Polymer Voltage Variable
Voltage Variable
Electrode Gap
Tin Plating
Copper Plating
Nickel Plating
Figure 7. PulseGuard suppressor structure
The PulseGuard suppressor products are
manufactured by creating a gap in an electrode that connects two end terminations.
The gap causes the two terminations to be
electrically discontinuous (current cannot
flow). Into the gap, a polymer-based material is back-filled.This voltage variable
material (VVM) has similar electrical charac-
Specifications, descriptions and illustrative material in this literature are as accurate as known at time of publication, but are
subject to change without notice. Littelfuse is a registered trademark of Littelfuse Incorporated.
teristics to the Zinc-Oxide material of the
MLV’s. Under normal circuit conditions, the
VVM acts like an insulator, but when an
ESD transient occurs, the VVM transitions
to a conductor and shunts the ESD to
Copyright © 2001 Littelfuse, Inc., All Rights Reserved. Printed in U.S.A. JANUARY 2002
Littelfuse, Inc.
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Des Plaines, IL 60016
(847) 824-1188