NEW PRODUCT
The Need for Better ESD Protection
The computer revolution has mandated the
need for more and more communication
links between electronic systems (computers,
peripherals, etc.), causing an associated explo-
sion in the magnitude of the data that must be
handled. Data transmission rates, by necessity,
have increased and will continue to increase.
Historically, transient voltage protection for
electronic systems evolved with changing
electronic technology. Prior to the use of solid
state components, vacuum tubes were used
as the building blocks of electronic systems.
These devices exhibited substantial survivability
to high voltage events such as ESD, indirect
lightning, electrical fast transients (EFT), and
system-generated transients. The need for
additional protection devices was low. However,
as transistors became the building blocks of
electronic systems, equipment such as modern
data processing equipment became increasingly
vulnerable to common ESD events.
This increased sensitivity of electronic systems
can be correlated to the decreasing size of their
circuitry. Simply put, as the physical geometry
of the circuitry decreased, so too did the
amount of energy needed to destroy the circuit’s
components (e.g., transistors, interconnects,
insulators, etc.). As a result, the need for a new
generation of products to protect extremely
vulnerable circuitry has never been greater.
While electronic components were evolving
toward their current state, a similar progression
was taking place with electronic signals and the
methods of information transmission. This has
resulted in increased signal bandwidths, higher
data transmission rates, and more complex
signal waveforms. In order to maintain the
integrity of these data transmissions, it is vital
for new circuit protection devices to remain
electrically transparent by not interfering with,
or degrading, the signals.
The first generation of transient protection
products was designed to mitigate the effects
of the direct lightning threat. However, the
source of today’s high voltage transients has
expanded beyond lightning to include such
threats as electrostatic discharge (ESD) and
electrical fast transients (EFT). Correspondingly,
the parameters of the new threats have changed
as well. For example, the current and voltage
rise time of lightning transients are orders of
magnitude slower than those experienced
during electrostatic discharge.
The fundamental question which now
needs to be asked is: Can the circuit
protection devices of the past provide
optimal protection for the circuits of today?
The Littelfuse Solution
The PulseGuard
®
suppressor line from Littelfuse
employs a voltage variable material (VVM) that
has a non-linear resistivity response to voltage
(see Figure 1). While the circuit is operating
normally, the ESD suppressor is electrically
transparent. When an ESD event occurs, the
VVM becomes conductive, shunting the ESD
energy away from the circuitry. After the ESD
energy has been dissipated, the suppressor
returns to a consistent high off-state resistance.
PulseGuard suppressors also offer very low
capacitance, assuring they will not cause
degradation to, or attenuation of, data signals.
This is vital given they will primarily be protecting
high-speed digital data lines. Typical effects
of higher capacitance when protecting with
alternate technologies include distortion of
the digital waveform, as seen in Figure 3.
Voltage (V)
Resistance (Ω)
Figure 1:
PulseGuard
Suppressor
Response Curve
Resistance vs. Voltage
Bulletin
