PROTECTION PRODUCTS
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www.semtech.com
PROTECTION PRODUCTS
STF201-22 & STF201-30
USB Downstream Port Filter & TVS
For EMI Filtering and ESD Protection
Description
Features
Schematic & Pin Configuration
Revision 9/2000
The STF201 is a combination EMI filter and line termi-
nation device with integrated TVS diodes for use on
downstream USB ports. It is constructed using a
proprietary technology that allows passive components
and TVS diodes to be integrated in the same package.
Each device will provide termination, filtering, and ESD
protection for one downstream USB port. The STF201
is an easily implemented solution for meeting the
requirements of revision 1.1 of the Universal Serial Bus
specification.
USB line termination is achieved with series 22W or
30W resistors on both the D+ and D- USB lines. These
resistors preserve signal integrity by matching the cable
impedance to that of the differential driver. The 15kW
pull-down resistors complete the termination circuit on
each line. They are required by the USB specification
to identify the line as a downstream connection. The
47pF capacitors are used to bypass high frequency
energy to ground and for edge rate control of the USB
signals. Finally, the STF201 contains TVS diodes for
ESD protection of both (D+ & D-) data lines and the
voltage bus (V
BUS
). The TVS diodes provide effective
suppression of ESD voltages in excess of 15kV (air
discharge) and 8kV (contact discharge) per IEC 61000-
4-2, level 4.
The small size and integrated feature of the STF201
minimizes required board space and increases system
reliability. The pin-out of the device allows easy imple-
mentation. The STF201 is suitable for use in USB
hubs, computers, peripherals, and portable devices.
Applications
Mechanical Characteristics
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USB Hubs
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Portable electronics
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Printers
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Monitors
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Servers, Desktop, and Notebook computers
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Bidirectional EMI/RFI filtering and line termination
with integrated ESD protection
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ESD protection for USB power (V
BUS
) and data lines
(D+ & D-) to IEC 61000-4-2 Level 4
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Filtering and termination for two USB data lines
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Different series resistors for impedance matching
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Low TVS operating voltage (5.25V)
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Low leakage current
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Low capacitance
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Solid-state technology
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EIAJ SOT23-6L package
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Molding compound flammability rating: UL 94V-0
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Marking : Marking Code
u
Packaging : Tape and Reel per EIA 481
S0T23-6L (Top View)
Circuit Diagram
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2000 Semtech Corp.
www.semtech.com
PROTECTION PRODUCTS
PROTECTION PRODUCTS
STF201-22 & STF201-30
Figure 1 - STF201 Circuit Diagram
Device Connection
The STF201 is designed to provide termination, EMI
filtering and ESD protection for two USB I/O lines. The
equivalent circuit diagram is shown in Figure 1. The
device is connected as follows:
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USB data lines are routed through the STF201 for
easy implementation and optimum pc board layout.
Pin 1 is connected to the voltage supply line. The
input of the D+ line is routed into pin 2 and out of
pin 5. The input of the D- line is connected at pin 3
and the output at pin 4. Pin 6 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.
USB Port Design Considerations
The Universal Serial Bus (USB) specification requires
termination and filtering components for proper opera-
tion. In addition, an open USB socket is vulnerable to
hazardous ESD discharges in excess of 15kV. These
discharges can may occur on the data lines or the
voltage bus. The STF201 is an easily implemented
solution designed to meet the termination & EMI filter
requirements of the USB specification revision 1.1. It
also provides ESD protection to IEC 61000-4-2, level
4.
A simplified USB port is shown in Figure 3. USB line
termination is achieved with series resistors on both
the D+ and D- lines. These resistors preserve signal
integrity by matching the cable impedance to that of
the differential driver. 15kW pull-down resistors are
used to identify a downstream port while an upstream
port is identified with a 1.5KW pull up resistor on either
the D+ (full speed devices) or the D- (low speed de-
vices) data line. Capacitors are used to bypass high
frequency energy to ground and for edge rate control
of the USB signals. TVS diodes are added for ESD
protection of both (D+ & D-) data lines and the voltage
bus (V
BUS
). A power distribution switch and voltage
regulator provide the power management functions of
the port.
Semtech provides a complete solution to simplify USB
port design (Figure 4). The STF201 & STF202 inte-
Figure 2 - STF201 Connection Diagram
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2
3
4
5
6
grate all of the components necessary for line termina-
tion, bidirectional EMI filtering, and ESD protection on
downstream (STF201) or upstream (STF202) ports.
The SC5826 is a dual port power switch that provides
individual or ganged port switching, fault reporting, and
inrush current limiting as required by the USB specifica-
tion. The SC5205 ULDO provides a stable voltage to
the USB controller.
Board Placement & layout Guidelines.
Board layout and placement of the STF201 play a
critical role in EMI & ESD suppression. Designing a
USB hub to meet EMI & ESD immunity requirements
requires a combination of optimum component place-
ment, trace routing, and good circuit design practices.
Some general guidelines are given below:
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Avoid running D+ & D- signal line traces near high
speed clock lines or similar signal lines.
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Avoid running critical signal lines near board edges.
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Locate the USB controller chip physically near the
USB connectors.
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Place the STF201 near the USB connector to
restrict transient coupling.
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Minimize the path length between the USB connec-
tor and the STF201 as well as between the USB
controller and the STF201.
Applications Information
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