3.3 Volt TVS Array
For ESD and Latch-Up Protection
PROTECTION PRODUCTS
Description
The SMF series of TVS arrays are designed to protect
sensitive electronics from damage or latch-up due to
ESD, lightning, and other voltage-induced transient
events. Each device will protect up to four lines operat-
ing at
3.3 volts.
The SMF3.3 is a solid-state devices designed specifi-
cally for transient suppression. It is constructed using
Semtech’s proprietary EPD process technology. The
EPD process provides low standoff voltages with
significant reductions in leakage currents and capaci-
tance over traditional pn junction processes. They offer
desirable characteristics for board level protection
including fast response time, low clamping voltage and
no device degradation.
The SMF3.3 may be used to meet the immunity re-
quirements of IEC 61000-4-2, level 4 (±15kV air, ±8kV
contact discharge). The small SC70-5L package
makes them ideal for use in portable electronics such
as cell phones, PDAs, and notebook computers.
SMF3.3
Features
ESD protection for data lines to
IEC 61000-4-2 (ESD) ±15kV (air), ±8kV (contact)
IEC 61000-4-4 (EFT) 40A (5/50ns)
Small package for use in portable electronics
Protects four I/O lines
Working voltage: 3.3V
Low leakage current
Low operating and clamping voltages
Solid-state EPD TVS technology
Mechanical Characteristics
EIAJ SC70-5L package
Molding compound flammability rating: UL 94V-0
Marking : Marking Code
Packaging : Tape and Reel
Applications
Cellular Handsets and Accessories
Cordless Phones
Personal Digital Assistants (PDAs)
Notebooks and Handhelds
Portable Instrumentation
Digital Cameras
Peripherals
MP3 Players
Circuit Diagram
1
3
4
5
Schematic & PIN Configuration
1
2
3
5
4
2
SC70-5L (Top View)
Revision 01/15/08
1
www.semtech.com
SMF3.3
PROTECTION PRODUCTS
Applications Information
Device Connection for Protection of Four Data Lines
The SMF3.3 is designed to protect up to four unidirec-
tional data lines. The device is connected as follows:
1. Unidirectional protection of four I/O lines is
achieved by connecting pins 1, 3, 4, and 5 to the
data lines. Pin 2 is connected to ground. The
ground connection should be made directly to the
ground plane for best results. The path length is
kept as short as possible to reduce the effects of
parasitic inductance in the board traces.
Due to the “snap-back” characteristics of the low
voltage TVS, it is not recommended that any of the I/O
lines be directly connected to a DC source greater than
snap-back votlage (V
SB
) as the device can latch on as
described below.
EPD TVS Characteristics
The SMF3.3 is constructed using Semtech’s propri-
etary EPD technology. The structure of the EPD TVS is
vastly different from the traditional pn-junction devices.
At voltages below 5V, high leakage current and junction
capacitance render conventional avalanche technology
impractical for most applications. However, by utilizing
the EPD technology, the SMF3.3 can effectively oper-
ate 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 (V
RWM
). During an ESD
event, the device will begin to conduct and will enter a
low impedance state when the punch through voltage
(V
PT
) 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.
SMF Circuit Diagram
1
3
4
5
2
Protection of Four Unidirectional Lines
When the TVS is conducting current, it will exhibit a
slight “snap-back” or negative resistance characteris-
tics due to its structures. This point is defined on the
curve by the snap-back voltage (V
SB
) and snap-back
current (I
SB
). To return to a non-conducting state, the
current through the device must fall below the I
SB
(approximately <50mA) and the voltage must fall below
the V
SB
(normally 2.8 volts for a 3.3V device). If a 3.3V
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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