SRDA05-6.T Ver la hoja de datos (PDF) - Semtech Corporation
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SRDA05-6.T Datasheet PDF : 9 Pages
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SRDA3.3-6 and SRDA05-6
PROTECTION PRODUCTS
Applications Information
Device Connection Options for Protection of Six High-
Speed Lines
The SRDA TVS is designed to protect four data lines
from transient overvoltages by clamping them to a
fixed reference. When the voltage on the protected
line exceeds the reference voltage (plus diode VF) the
steering diodes are forward biased, conducting the
transient current away from the sensitive circuitry.
Data lines are connected at pins 1, 2, 4, 5, 6 and 7.
The negative reference is connected at pin 8. These
pins should be connected directly to a ground plane on
the board for best results. The path length is kept as
short as possible to minimize parasitic inductance.
The positive reference is connected at pins 2 and 3.
Data Line Protection Using Internal TVS Diode as
Reference
In the case of the SRDA3.3-6, pins 2 and 3 are
connected internally to the cathode of the low voltage
TVS. It is not recommended that these pins be directly
connected to a DC source greater than the snap-back
votlage (VSB) as the device can latch on as described
below.
EPD TVS IV Characteristic Curve
IPP
EPD TVS Characteristics
These devices are constructed using Semtech’s
proprietary EPD technology. By utilizing the EPD tech-
nology, the SRDA3.3-6 can effectively operate at 3.3V
while maintaining excellent electrical characteristics.
The EPD TVS employs a complex nppn structure in
contrast to the pn structure normally found in tradi-
tional silicon-avalanche TVS diodes. Since the EPD
TVS devices use a 4-layer structure, they exhibit a
slightly different IV characteristic curve when compared
to conventional devices. During normal operation, the
device represents a high-impedance to the circuit up to
the device working voltage (VRWM). During an ESD
event, the device will begin to conduct and will enter a
low impedance state when the punch through voltage
(VPT) is exceeded. Unlike a conventional device, the low
voltage TVS will exhibit a slight negative resistance
characteristic as it conducts current. This characteris-
tic aids in lowering the clamping voltage of the device,
but must be considered in applications where DC
voltages are present.
When the TVS is conducting current, it will exhibit a
slight “snap-back” or negative resistance characteris-
tics due to its structure. This point is defined on the
VBRR
ISB
IPT
IR
IBRR
VRWM VSB VPT VC
curve by the snap-back voltage (V ) and snap-back
SB
current (I ). To return to a non-conducting state, the
SB
current through the device must fall below the ISB
(approximately <50mA) and the voltage must fall below
the V (normally 2.8 volts for a 3.3V device). If a 3.3V
SB
TVS is connected to 3.3V DC source, it will never fall
below the snap-back voltage of 2.8V and will therefore
stay in a conducting state.
2008 Semtech Corp.
5
www.semtech.com
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