Datasheet
USB
Hub Port
Transceiver
27O
27O
15kO
15kO
SN65220 or
½ SNx5240
GND
A
B
D+
D-
USB
Down Stream
Transceiver
27O
27O
SN65220 or
½ SNx5240
GND
A
B
D+
D-
1.5kO
(1)
1.5kO
(2)
1) Full-speed only
2) Low-speed only
SN65220
,
SN65240
,
SN75240
SLLS266H –FEBRUARY 1997–REVISED MAY 2015
www.ti.com
11 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
11.1 Application Information
The universal serial bus (USB) has become a popular solution to connect PC peripherals. USB allows devices to
be hot-plugged in and out of the existing PC system without rebooting or turning off the PC. Because frequent
human interaction with the USB system occurs as a result of its attractive hot-plugging ability, there is the
possibility for large ESD strikes and damage to crucial system elements. The ESD protection included on the
existing hardware is typically in the 2-kV to 4-kV range for the human body model (HBD) and 200-V to 300-V for
the machine model (MM). The ESD voltage levels found in a normal USB operating environment can exceed
these levels. The SN75240, SN65240, and SN65220 devices will increase the robustness of the existing USB
hardware to ESD strikes common to the environment in which USB is likely to be used.
11.2 Typical Application
Figure 5 illustrates a typical USB system and application of the SN75240, SN65240, and SN65220 devices.
Connections to pin A from the D+ data line, pin B from the D– data line, and the device grounds from the GND
line that already exists are necessary to increase the amount of ESD protection provided to the USB port.
The design of the suppressor gives it very low maximum current leakage of 1 μA, a very low typical capacitance
of 35 pF, and a standoff voltage minimum of 6 V. Because of these levels, the SN75240, SN65240, and
SN65220 devices will provide added protection to the USB system hardware during ESD events without
introducing the high capacitance and current leakage levels typical of external transient voltage suppressors. The
addition of an SN75240, SN65240, or SN65220 device is beneficial to both full-speed and low-speed USB 1.1
bandwidth standards.
Figure 5. Typical Application Schematic for ESD Protection of USB Transceivers
11.2.1 Design Requirements
For this design example, use the parameters listed in Table 1 as design parameters.
Table 1. Design Parameters
DESIGN PARAMETER EXAMPLE VALUE
Minimum breakdown voltage (TVS) 6.5 V
Maximum supply voltage (USB transceiver) 5.5 V
Typical junction capacitance (TVS) 35 pF
Maximum data rate (USB transceiver) 12 Mbps
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Product Folder Links: SN65220 SN65240 SN75240