4© 2012 Semtech Corporation
www.semtech.com
PRELIMINARY
PROTECTION PRODUCTS
uClamp3301H
Applications Information
Semtech Low Voltage TVS
Conventional TVS diodes are silicon avalanche, p-n
junction devices designed to operate at voltages as
low as 5 volts. However, many of today's
semiconductor devices operate at voltages below 5
volts, and thus require lower voltage protection
devices. Unfortunately, for operating voltages below 5
volts, conventional TVS diode technology becomes
impractical. This is due to the adverse effects of high
leakage current and high capacitance caused by the
high impurity concentrations that are needed to lower
the device voltage below 5 volts. Semtech's
proprietary low voltage EPD device technology was
developed to provide protection for today's circuits
operating at voltages below 5 volts. Unlike
conventional TVS diodes, the EPD device utilizes a
complex four layer (n-p-p-n) structure. The
construction of these devices results in very low
operating voltage without the adverse effects
mentioned above.
Device Operation
Since the EPD TVS devices use a 4-layer structure,
they exhibit a slightly different IV characteristic curve
when compared to conventional devices. Figure 1
compares the IV characteristic curves of a low voltage
TVS with a working voltage (V
RWM
) of 3.3 volts to a
conventional device with a working voltage of 5 volts.
During normal operation, each device represents a
high-impedance to the circuit up to its working voltage.
During an ESD event, they will begin to conduct and
will enter a low impedance state. For the 3.3 volt
device, this happens when the punch-through voltage
(V
PT
) is exceeded. Unlike a conventional 5 volt device,
the low voltage TVS will exhibit a slight negative
resistance characteristic as it conducts current. This
characteristic aids in lowering the clamping voltage of
the device. However, the device can latch up if a DC
bias voltage is present. The reason being that in order
for the device to turn off, the voltage must fall below
the snap-back voltage (V
SB
). This value is normally a
minimum of 2.8 volts. If the device is biased above
the 2.8 volts, it will never fall below the snap-back
voltage and will therefore stay in a conducting state.
Figure 1 - 3.3 volt vs. 5 volt TVS IV Curve
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Voltage - V (V)
Current - I (A)
Semtech
5 Volt TVS
V
PT
V
RWM
V
SB
V
RWM
V
BR
Semtech 3.3 Volt TVS
Low Voltage TVS
¾ Working Voltage (V
RWM
): Maximum rated
operating voltage at which the device will
appear as a high impedance to the
protected circuit.
¾ Punch-Through Voltage (V
PT
): Minimum
rated voltage at which the device will
become a low impedance (i.e. Minimum
Turn-On Voltage). When V
PT
is exceeded,
the device will conduct.
¾ Snap-Back Voltage (V
SB
): Minimum rated
voltage when the device is in a conducting
state measured at I
SB
= 50mA. This
voltage is less than the working voltage.
The voltage must fall below V
SB
for the
device to turn off.
¾ Clamping Voltage (V
C
): Maximum voltage
drop across the device at a defined peak
pulse current (I
PP
). This is the voltage
seen by the protected circuit during a
transient event.
